Case Studies

The heart and soul of The LASIK Handbook are the 105 cases, which are presented for study. The cases represent a broad array of pathology and experience. They are indexed by findings or characteristics with the intention of making them easily accessible for reference when a patient with similar findings presents for refractive surgery. The indexes can be found at the beginning of the book. The cases have been prepared by the editor and the contributors, and reflect the opinions and preferences of the individual author. The reader is presented with one way—but not necessarily the only way—to work the case. Each of your patients is unique and surgery should always be designed with your specific patient in mind.

Easier cases will appear at the beginning of the study section. Preoperative decision-making is emphasized in the first half of this section. The later cases emphasize intraoperative and postoperative management. In addition to print illustrations, some cases will have references directing the reader to illustrative or instructional videos.

It can be assumed in each case that the risks of surgery have been presented to the patient, that they were understood, and that the patient wishes to proceed with surgery. Unless otherwise indicated, the patient has been out of contact lenses long enough for the given refractions to be stable. That said, not every patient presented is a candidate for LASIK surgery. The reader will need to make that determination.

For the sake of discussion, a preoperative estimate of residual stromal bed (RSB) for microkeratome cases is determined as preoperative pachymetry minus both the plate thickness and the non-nomogram-adjusted estimate of the stromal ablation. Depending on the specific microkeratome, the actual flap thickness may be greater or less than the plate would indicate. The reader should be aware that this is only an estimate made to determine a patient’s suitability for surgery and is not a substitute for direct measurement or knowledge of specific microkeratome performance for a specific surgeon. Many factors previously discussed (see Chapters 1 and 4) will impact the actual flap thickness and residual stromal bed (RSB) thickness.

Over the many years during which these cases have been collected, some trends have changed. For example, there is little, if any, scientific basis for the belief that pupil size is a
factor causing postoperative nighttime glare and haloes. Many surgeons use the largest treatment zone that anatomical constraints will allow regardless of pupil size. Some accomplished surgeons do not even measure pupil size. Other surgeons prefer to tailor the treatment zone to the pupil size among other factors. Another example of a management change is that over time many surgeons have found no difference in night vision with either a 6.0- or 6.5-mm treatment zone as long as a blend zone to at least 8.0 mm is performed. They prefer to use the smaller treatment zone to conserve stromal tissue. Finally, there has been a heightened sensitivity about avoiding ectasia, and to that end surgeons are more conservative about preserving the RSB. While 250 µm was considered adequate thickness in years past, some surgeons now routinely prefer 275 µm or even 300 µm; and some are more likely to advise against LASIK for even minor topography abnormalities. While the scenarios presented in these cases are timeless, opinions about the optimal management strategies should be expected to change over time.

The best learning experience for case study will occur if the reader, with paper and pencil in hand, actively studies each case history and examination and develops an independent surgical strategy before reading the discussion and treatment plan. The reader should work the case as if the patient had presented in the office. One should identify the variables or challenges that must be considered when developing a surgical plan. The key questions to be answered in each case include: Is this patient a good candidate for LASIK surgery or is another approach better or safer? What correction should be treated? How should the flap be created? What treatment zone is most appropriate? What is the approximate ablation depth? What is the overall plan for surgery in the language the scrub technician and laser engineer can use? For example, specify the microkeratome ring and plate sizes or femtosecond flap thickness and diameter, as well as the strategy for excimer ablation. Are there any special considerations in the case?

Each case is followed by a narrative discussion and most cases provide a tabular summary of a proposed surgical plan. The equipment used to carry out the plan is specified. At the conclusion of each case, a series of take-home points is listed.

While one could work the cases in order, an alternative way to proceed is to use the various case indexes. Two charts are provided: one for preoperative patient characteristics and one that contains intraoperative and postoperative conditions. Readers can match the variables observed in a proposed patient with those variables in the index and find the relevant cases in the handbook. For example, a reader concerned about the management of a patient with corneal neovascularization can locate this variable in the index and be directed to all of the cases in which corneal neovascularization is discussed. These indexes will hopefully allow the reader to easily access those specific cases and discussions that will be most relevant. It is our hope that studying these cases will be a satisfying experience, both challenging and rewarding.

▪ Preoperative Decision Making

CASE 1

A 35-year-old woman with a history of myopia and a 20-year history of soft contact lens wear expresses interest in LASIK surgery. Assume she has been out of her contacts long enough for the refractions to have stabilized.

W	OD – 6.25 20/20+ OS – 6.25 20/20-		Uncorrected Va 20/400 OU
M	OD – 5.50 + 0.50 × 40° 20/15 OS – 5.25 20/15-
C	OD – 5.25 20/15 OS – 4.75 20/15-
K	OD 44.50 × 180°/44.87 × 90° OS 44.50 × 180°/44.75 × 90°
Pachymetry OD 541 µm OS 531 µm		Topography No cone OU		Scotopic Pupils OD 5.0 mm OS 5.0 mm

Additional Examination

Excellent exposure with a normal slit-lamp examination, intraocular pressure (IOP), and fundus examination.

Discussion

This is a fairly straightforward patient with myopia. While astigmatism appears in the manifest refraction, the cycloplegic (C) refraction will be used in determining the laser treatment. Many surgeons prefer not to change the cylinder from the manifest refraction. Alternatively, the patient could have a post-cycloplegic refraction prior to surgery to check the astigmatism.

The small scotopic pupil allows the surgeon to choose a small treatment zone. This will help preserve corneal tissue. Many surgeons, however, do not believe that pupil size is a significant risk factor affecting the quality of night vision and choose to use the largest treatment zone possible, given anatomical constraints. Because there is no peripheral pathology and the corneal diameter is presumably of normal size, a larger ring can be used. This will create a larger flap that may be desirable in the event future retreatment is necessary. Notice that this patient appears to be moderately overcorrected in her present spectacles. Relaxing accommodation may take some time. It is helpful to warn the patient preoperatively that the full vision correction will not occur instantaneously, but may occur over several days to a couple of weeks.

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	8.5 or 9.5 mm	8.5 or 9.5 mm	If perilimbal neovascularization or a small corneal diameter, choose 8.5-mm ring
Plate size	160 or 180 µm	160 or 180 µm	Hansatome flap may be thinner than plate size
Ablation zone	6.0 mm	6.0 mm	Ablation zone > scotopic pupil
Cycloplegic RX	-5.25 diopters (D)	-4.75 D
Calculations: Sphere in cycloplegic refraction is reduced by the VISX nomogram Adjusted correction is entered into VISX laser	-5.25 × 6% = -0.315 -5.25 + 0.32 = -4.93 -4.93 D	-4.75 × 6% = -0.285 -4.75 + 0.29 = -4.46 -4.46 D	Refer to Chapter 7 on the VISX laser and the nomogram (Table 7.1, page 75) for the amount of reduction
Ablation depth use non-nomogram-adjusted spherical equivalent	From Table 7.3: 66 µm Using calculation: -5.25 D × 12 µm/D = 63 µm	From Table 7.3: 60 µm Using calculation: -4.75 D × 12 µm/D = 57 µm	Most cases will use the calculation method for ablation depth
Residual stromal bed (RSB)	541 µm – 160 µm – 66 µm = 315 µm >250 µm	531 µm – 160 µm – 60 µm = 311 µm >250 µm	Intraoperative pachymetry best for RSB calculation

Take-Home Points

1	Always use the cycloplegic refraction before making the nomogram adjustment in calculating the ablation depth.
2	Using an ablation zone slightly larger than the scotopic pupil minimizes tissue removal. Be aware that there is a trend toward relying less on pupil size to determine treatment zone, given the lack of scientific evidence to support pupil size as a factor related to postoperative night vision disturbance.
3	A larger flap is desirable in case a retreatment requires a larger treatment zone. However, when the flap edge is near the limbus, the flap may be more difficult to relift.
4	Warn the patient overcorrected in spectacles or glasses about the possibility of a slower postoperative visual recovery.

CASE 2

A 38-year-old woman has worn rigid gas-permeable (RGP) hard contact lenses for 15 years and presents for LASIK evaluation. The patient is highly myopic and feels vulnerable and disabled without her contact lenses. The past ocular history has been completely uneventful. There has specifically been no history of corneal ulceration, abrasion, or keratitis. Her general health is excellent. After consultation and detailed explanation of the risks of surgery, the patient is anxious to proceed with LASIK. She is kept out of contact lenses until the corneal contour and refraction stabilize.

OD – 10.25 + 1.25 × 4° 20/25-

OS – 10.25 + 0.75 × 150° 20/30-

Uncorrected Va

CF 3′

OD – 9.50 + 0.50 × 180° 20/15-

OS – 9.75 + 0.75 × 135° 20/15

OD – 9.75 + 0.50 × 160° 20/15-Vertex distance 12 mm

OS – 9.50 + 0.50 × 120° 20/20 Vertex distance 12 mm

OD 44.87 × 90°/44.50 × 180°

OS 43.87 × 40°/44.50 × 130°

Pachymetry

OD 564 µm

OS 555 µm

Topography

Against-the-rule astigmatism OU; no cone OU

Scotopic Pupils

OD 5.0 mm

OS 5.0 mm

Additional Examination

The external eye appears healthy. The lids are lax and the palpebral fissure is wide. The exposure is excellent. The slit-lamp examination shows subepithelial haze OD with minimal thinning near the limbus superiorly extending for 1 clock hour. There is no active keratitis and no corneal neovascularization. The anterior segment is otherwise normal in both eyes. The lids and lashes are normal with no evidence of blepharitis or meibomian gland disease. The IOP and dilated fundus examinations are normal.

Discussion

The treatment of high myopia requires an adequate corneal thickness and corneal steepness in order to ensure that the cornea will not be too thin or flat postoperatively. If the corneal thickness is inadequate, the cornea is too flat, or the degree of myopia is too great, consider an alternative to LASIK such as insertion of a phakic IOL (see Chapter 15 on alternatives to LASIK). Clear lens exchange in an extreme myope may have an unacceptably high risk of retinal detachment over the long term.

The highly myopic patient may have excessive myopic correction in spectacles or contact lenses, which can only be uncovered with a full cycloplegic refraction. It is also important to measure the vertex distance. Most excimer lasers have a default vertex distance at the spectacle plane. If the measured vertex distance is different than the default, an adjustment is required. For greatest accuracy, central pachymetry should be measured at the time of surgery. Do not rely on the pachymetry performed on a different day to calculate flap thickness. Many factors including contact lens wear, time of day, and ambient humidity can impact corneal thickness.

To estimate the postoperative corneal contour, multiply the spherical equivalent by 0.7 or, to be even more conservative, 0.8. Subtract this product from the average of the preoperative keratometry values. If the result is <35.00 D, the cornea may be too flat after surgery. Highly myopic patients are more likely to regress postoperatively; therefore, in anticipation of possible regression, it is useful to make certain that there is sufficient corneal steepness and thickness to support retreatment. If there is not much room for retreatment, the patient must be warned of the limitation on enhancement and the consequence of untreated regression. Because the pupil is rather small in this case, a smaller ablation zone can be used. This will mean the ablation will not be as deep and will leave more residual stroma.

This patient has an old scar in the right cornea. She denies inflammation, infection, or erosion. Because the scarring is superficial and well out of the ablation zone, it is not a contraindication to surgery. The surgeon should always attempt to determine the cause of such a scar by obtaining a complete history and performing a thorough examination.

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm	Hansatome
Plate size	160 µm	160 µm	Hansatome flap is usually thinner than the plate thickness, especially on the second eye
Ablation zone	6.0 mm	6.0 mm	VISX STAR S4
Calculations with nomogram correction (enter into VISX)	-9.50 D × 11% = 1.05 -9.75 + 1.05 = 8.70 -8.70 + 0.50 × 180	-9.25 × 11% = 1.02 -9.50 + 1.02 = 8.48 -8.48 + 0.50 × 135	Use cylinder axis of the manifest or split the difference between M and C
Ablation depth	9.50 D × 12 µm/D = 114 µm	9.25 D × 12 µm/D = 111 µm	Always use non-nomogram-adjusted spherical equivalent to calculate ablation depth
RSB	564 µm – 128 µm – 114 µm = 322 µm >250 µm	555 µm – 123 µm – 111 µm = 321 µm >250 µm	RSB calculated using the central flap thickness measured in surgery

Take-Home Points

1	Make certain the patient will have enough RSB for retreatment and will have adequate corneal curvature to support good visual function.
2	Always use the non-nomogram-adjusted spherical equivalent to calculate the ablation depth. Do not rely on the ablation depth calculated by the laser for conventional LASIK.
3	Measure pachymetry intraoperatively. Do not rely on a central pachymetry measurement made on a different day.
4	Do not compromise on patient safety. Consider alternatives to LASIK when necessary. Straight talk with the patient is always the best approach.

Proceed to Case 74 to find out what happened to this patient.

CASE 3

A 40-year-old woman comes desiring refractive surgery. She has worn rigid gas-permeable contact lenses (RGPCLs) for more than 15 years and is becoming increasingly intolerant to her contact lenses. She stopped wearing her RGPCLs 4 weeks ago in preparation for her refractive evaluation. She has been treated in the past for Graves’ disease. She currently takes levothyroxine (Synthroid) and occasional artificial tears.

OD – 4.25 + 1.00 × 78°

OS – 2.50 + 0.50 × 125°

Uncorrected Va

20/400

20/200

OD – 4.75 + 1.25 × 70° 20/20

OS – 3.25 + 0.75 × 135° 20/20

OD – 5.00 + 1.50 × 75° 20/20

OS – 3.00 + 0.50 × 125° 20/20

OD 41.00 × 170°/43.00 × 80°

OS 42.12 × 35°/43.75 × 125°

Pachymetry

OD 548 µm

OS 552 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 6.9 mm

OS 6.8 mm

Additional Examination

Her corneas are clear without staining. Her eyelids show 2-3+ blepharitis with meibomianitis. Changes are seen on her eyelids and face, consistent with acne rosacea. There is mild upper lid retraction OU without proptosis. The remainder of her ocular examination is normal.

Discussion

This patient’s case illustrates a number of important clinical points. This patient has been a long-time RGPCL wearer. These rigid contact lenses may alter the shape of the cornea and mask astigmatism and myopia. Therefore, the surgeon must be sure that the refraction is stable and accurate. The magnitude and axis of the astigmatism must be consistent between the manifest refraction, cycloplegic refraction, and the corneal maps. The corneal maps should show regular astigmatism and no signs of corneal warping. If there is any doubt as to whether the contact lenses have altered the refraction and corneal shape, the patient should stay out of the contacts for a longer period of time and return for repeat refraction and maps until they are all stable and consistent.

This patient is also at risk for postoperative dry eyes. A 40-year-old woman is undergoing early hormonal changes that decrease tear production. She also has increased corneal exposure due to lid retraction resulting from thyroid disease. Lastly, she has posterior blepharitis and abnormal meibomian glands that produce an abnormal lipid component to her tear film and therefore tear film instability. The decreased tear production that normally accompanies a denervated post-LASIK cornea may further contribute to this patient’s postoperative dry eye. The patient should be treated aggressively after surgery if signs of dry eye and corneal staining occur. This treatment could include frequent nonpreserved artificial tears and/or topical cyclosporine. Punctal occlusion should be avoided until the posterior blepharitis is treated.

Lastly, this patient has posterior blepharitis as a result of the acne rosacea. This increases the chance for diffuse lamellar keratitis (DLK). The rosacea should be treated with eyelid hygiene twice a day, combined with oral doxycycline or minocycline. LASIK should be delayed until the lids show clinical improvement.

This patient is a good candidate for custom ablation. Her refractive error falls well within the range for custom ablation and her refraction from the wavefront aberrometer is consistent with her manifest and cycloplegic refraction. She shows enough spherical aberration and coma to benefit from the wavefront-guided treatment. Her corneas are mildly flat and therefore a 9.0-mm suction ring is chosen on the Becton Dickinson K-3000 microkeratome. A 160-µm plate is used to create a slightly thinner flap to avoid any possible masking effects that a thicker flap would have on a custom ablation.

Surgical Plan

	Right Eye	Left Eye	Comments
Considerations	Evaluate for dry eye, treat for rosacea. Proceed only if surface is healthy
Ring size	9.0 mm	9.0 mm	BD K-3000
Plate size	160 µm	160 µm	Actual flap thickness is usually thinner
Ablation zone	6.5 mm with blend zone	6.5 mm with blend zone	Alcon laser Pupils >6.5 mm
Spherical equivalent	-4.25 D	-2.75 D
CustomCornea treatment based on Alcon wavefront measurements	-4.39 D sphere 1.30 D × 66°	-2.95 D sphere 0.69 D × 132°	The Alcon CustomCornea suggests a 6% reduction of sphere and cylinder; treatment is based on the wavefront data
Nomogram adjustment (6%) at corneal plane in minus cylinder	-2.76 – 1.19 × 156°	-2.04 – 0.65 × 42°
Ablation depth	80 µm	56 µm	The Alcon software calculates the ablation depth
RSB	548 µm – 160 µm – 80 µm = 308 µm	552 µm – 160 µm – 56 µm = 336 µm	>250 µm

Take-Home Points

1	Be sure that the patient has been out of RGPCLs long enough to allow the cornea to assume its normal shape.
2	Look for factors that could predispose a patient to postoperative dry eyes and pretreat the patient appropriately.
3	Treat a patient with rosacea with preoperative oral tetracycline and lid hygiene.
4	Consider wavefront-guided ablation if the wavefront-derived refraction is consistent with the manifest refraction and the patient demonstrates higher order aberrations (HOAs).

CASE 4

A 38-year-old police detective had worn RGPCLs for 15 years. He was eager to become less dependent on his contact lenses and glasses prompting a LASIK consultation. He understood the future need for reading glasses and the other associated risks of surgery. After 1 month, his refractive error had stabilized and surgery was planned.

OD – 2.50 20/20-

OS – 2.50 20/20-

Uncorrected Va

20/200

OD – 3.75 + 1.25 × 87° 20/15

OS – 3.25 + 0.75 × 85° 20/15-

OD – 3.50 + 1.00 × 85° 20/15-

OS – 3.25 + 0.75 × 90° 20/15

OD 42.75 × 177°/43.75 × 87°

OS 43.00 × 180°/44.00 × 90°

Pachymetry

OD 513 µm

OS 509 µm

Topography

Regular with-the-rule astigmatism OU

Scotopic Pupils

OD 7.0 mm

OS 7.0 mm

Discussion

While the pupils are somewhat large and the cornea somewhat thin, the correction is low enough such that there is room for a large zone with a blend to extend the treatment to 8.0 mm. This patient, due to his profession, should be specifically warned about the possibility of night vision problems and the effect of a traumatic injury to the flap. He should also be considered for a custom procedure, which may reduce the likelihood of postoperative glare and haloes.

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm
Plate size	160 µm	160 µm	Hansatome flap usually thinner than 160 µm
Ablation zone	6.5 mm with blend (6.0 mm with blend is an alternative)	6.5 mm with blend (6.0 mm with blend is an alternative)	VISX laser 7.0-mm pupil
Calculations with nomogram correction (enter into VISX laser)	3.00 D × 7% = 0.21 D 3.50 D – 0.21 D = 3.29 D -3.29 + 1.00 × 85	2.88 D × 7% = 0.20 D 3.25 D – 0.20 D = 3.05 D -3.05 + 0.75 × 90
Ablation depth	45 µm + 8 µm = 53 µm	43 µm + 8 µm = 51 µm
RSB	513 µm – 160 µm – 53 µm = 300 µm >250 µm	509 µm – 160 µm – 51 µm = 298 µm >250 µm	If actual flap is thinner than 160 µm, RSB will be even greater

Take-Home Points

1	Emphasize those risks that are relevant to a given patient based on the patient’s work and leisure activities.
2	Design the surgery to minimize those risks. In this case, use a treatment zone larger than the scotopic pupil, use the largest zone permissible given the anatomical constraints, and/or consider a custom treatment.

Proceed to Cases 61 and 62 to find out what happened to this patient.

CASE 5

A 33-year old woman with an 18-year history of soft contact lens wear presented with a 6-month history of contact lens intolerance. She complained of itching, tearing, and burning in both eyes for the previous 6 months. She could not wear contact lenses because of discomfort and wished to consider refractive surgery.

OD -6.50 + 0.50 × 95

OS -6.25 + 0.50 × 85

Uncorrected Va

20/400 OU

OD -6.00 sphere

OS -6.50 + 0.50 × 80

OD -5.75 sphere

OS -6.25 + 0.50 × 80

OD 42.50 × 180/43.25 × 90

OS 42.50 × 180/43.25 × 90

Pachymetry

OD 556 µm

OS 549 µm

Topography

OD 0.75 D regular cyl at 90; normal elevation

OS 1.00 D regular cyl at 80; normal elevation

Scotopic Pupils

6.0 mm OU

Additional Examination

The bulbar conjunctiva showed 1+ injection and the superior palpebral conjunctiva showed 2-3+ injection both eyes. Her corneas were both clear and her tear film appeared adequate.

Discussion

This 33-year-old female is, in general, an excellent candidate for refractive surgery. Her contact lens intolerance is largely related to her chronic allergic conjunctivitis. Contact lens wear can exacerbate the signs and symptoms of allergy. Therefore, removing the need for contact lenses with refractive surgery is desirable. Before contemplating laser surgery, she will require treatment for her allergic conjunctivitis. Topical mast cell stabilizers and antihistamines can help to control the inflammation in her conjunctiva. It is optimal to have a quiet and calm eye before performing refractive corneal surgery.

When using the WaveLight laser, the patient’s data is entered into the SurgiVision DataLink program. The planned correction is based on the manifest (M) refraction, cycloplegic (C) refraction, and data obtained by the Alcon wavefront aberrometer. The aberrometer has proven to be an excellent auto refractor and is a useful guide in treatment planning when combined with the manifest and cycloplegic refractions. Once the surgeon’s treatment plan is calculated, the degree of spherical and cylindrical refractive error is entered into the SurgiVision program. The DataLink program then modifies the treatment based on the patient’s age, refraction, keratometry, and the doctor’s individual nomogram. The suggested DataLink treatment plan is then programmed into the laser.

Surgical Plan

Ziemer Femto LDV flap diameter: OD 9.0 mm OS 9.0 mm

Flap thickness: OD 110 µm OS 110 µm

Ablation zone: 6.5-mm optical zone with a 1.25-mm transition zone and a total ablation area of 9.0 mm OU

Ablation depth: OD 84.17 µm OS 91.08 µm

Original planned treatment: OD -6.00 + 0.50 × 110 OS -6.50 + 0.50 × 85

DataLink-adjusted treatment: OD -5.75 + 0.50 × 110 OS -6.25 + 0.50 × 85

Measured RSB: OD 360 µ OS 346 µ

Take-Home Points

1	Allergic conjunctivitis is a common cause for contact lens intolerance. Care should be taken to adequately treat the allergic conjunctivitis until the conjunctiva and ocular surface looks quiet. Attention should also be paid to avoid treating seasonal allergy patients during their high allergy season.
2	The Alcon WaveLight laser platform works well with the integrated SurgiVision DataLink program. The DataLink program uses the surgeon’s specific nomogram to adjust treatment parameters before entering this data into the laser. The entered data is therefore based upon analyzed outcomes from the surgeon’s specific databank.

CASE 6

A 28-year-old woman presents for laser vision correction. Her past medical history is negative, and her past ocular history is significant for 15 years of soft toric disposable contact lens wear. There is no history of prior ocular trauma, infection, or prior surgery. She is not currently pregnant or nursing. She takes no systemic or ocular medications and has no known drug allergies. She last wore her contact lenses 3 weeks ago.

OD – 4.50 + 0.50 × 90° 20/25

OS – 4.75 + 0.75 × 90° 20/30

Uncorrected Va

20/400

OD – 4.75 + 0.50 × 90° 20/20

OS – 5.25 + 0.75 × 85° 20/20

OD – 4.75 + 0.50 × 90° 20/20

OS – 5.25 + 0.75 × 90° 20/20

OD 40.50 × 90°/40.00 × 180°

OS 41.50 × 90°/40.50 × 180°

Pachymetry

OD 535 µm

OS 540 µm

Topography

Regular bow-tie OU

Scotopic Pupils

7.0 mm OU

Additional Examination

The patient does not have deep-set eyes. The palpebral fissure is wide OU. The slit-lamp examination reveals a normal cornea OU with no evidence of guttata or keratoconus (KC). The lenses are clear, and the IOP is 16 mmHg OU by applanation tonometry. The dilated funduscopic examination is unremarkable. Orbscan evaluation reveals posterior elevation of 22 µm in the right eye, and 26 µm in the left eye.

Discussion

This patient is a very good candidate for laser vision correction, especially LASIK, provided that several points are considered. From a historical perspective, the patient has no other complicating medical or ophthalmic conditions. The length of time that she has been out of her toric contact lenses is adequate with the minimum being 2 weeks. The refractive error is within the range for LASIK, and more importantly has been stable over the past year. Stability is defined as a <0.5 D change over the previous 12 months. The corneal thickness is adequate for LASIK at this level of myopia. The topographical analysis is normal in each eye. Orbscan measurements of the posterior elevation may help identify corneas that have forme fruste keratoconus (FFKC). Remember that posterior elevation in an untreated cornea of 50 µm (0.050 mm) or greater above a “best-fit sphere” are strongly suggestive of FFKC (see discussion of topography in Chapter 2). Values between 40 and 50 µm are suspicious and other criteria should be used to determine whether or not a patient is a candidate for LASIK. A posterior elevation of 22 and 26 µm as in this case is not a reason for concern.

Several issues regarding this patient need to be addressed. The patient’s keratometry values are fairly flat. In general, 1 D of excimer ablation will result in flattening of the keratometry by 0.7 to 0.8 D. Although controversial, it is wise to keep the corneal curvature above 35.00 D following LASIK surgery. In this case, the expected postoperative keratometry values should be approximately 36.50 D. Another problem with flat corneal contour relates to the creation of the corneal flap. With a very flat cornea, there is a higher incidence of a small flap or possibly a free cap. To minimize this possibility, a larger diameter suction ring should be used, such as a 9.5-mm ring. The femtosecond laser is a useful alternative, because its use is not dependent on corneal contour.

Another issue is the large pupil size. The Bausch & Lomb (B&L) laser has the capability of treating a wide ablation zone, larger than the scotopic pupil size, and this may help reduce the incidence of glare, haloes, and starbursts. The optical zone determines the depth of ablation, according to Munnerlyn’s formula and, therefore, caution is urged in selecting the appropriate zone. The optical zone can be set from 4.5 to 8.0 mm plus a blend zone of 3 additional mm. Therefore, a 6-mm optical zone provides an ablation of 9 × 9 mm, larger than almost all scotopic pupil size. It is the most commonly used optical zone size. In this patient, with 7-mm scotopic pupils, we would select a 6-mm optical zone because the total ablation area is larger than the scotopic pupil size. The selection of a larger optical zone would probably not provide additional benefit and only consume more corneal tissue.

The B&L laser is very accurate. We do not adjust the desired refraction with any nomogram, but each surgeon should make this determination after a careful analysis of their data. We often adjust the target refraction in patients <30 years of age to +0.50 D.

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm	Flat contour; use 9.5 to prevent free cap
Plate size	160 µm	160 µm	Hansatome usually cuts 100-120 µm flap
Optical zone	6.0 mm	6.0 mm	B&L laser
Transitional zone	9.0 mm	9.0 mm	Total ablation larger than scotopic pupil
Enter into B&L laser, no nomogram adjustment needed	-5.25 + 0.50 × 90°	-5.75 + 0.75 × 85°	Target + 0.50 D postoperatively
Ablation depth RSB	95 µm 535 µm – 160 µm – 95 µm = 280 µm >250 µm	103 µm 540 µm – 160 µm – 103 µm = 277 µm >250 µm

Take-Home Points

1	Use a 9.5-mm ring for flat corneas in order to prevent free flaps.
2	Select the appropriate optical zone size in order to provide adequate coverage of the scotopic pupil.
3	Always measure intraoperative pachymetry.

CASE 7

A 38-year-old man is interested in refractive surgery. He occasionally wears soft contact lenses. His refraction has been stable for over a year. He has no health problems.

OD – 3.75 + 1.75 × 89°20/20+

OS – 4.75 + 2.00 × 81° 20/15

Uncorrected Va

CF 5′

OD – 3.75 + 1.75 × 100°20/15

OS – 4.50 + 2.00 × 90° 20/15

OD – 3.75 + 2.00 × 100°20/15

OS – 4.50 + 2.00 × 85° 20/15-

OD 39.50/41.00 × 94°

OS 39.12/41.37 × 94°

Pachymetry

OD 550 µm

OS 550 µm

Topography

No cone OU

Scotopic Pupils

OD 6.0 mm

OS 6.0 mm

Additional Examination

The patient has slightly deep-set eyes, with lax lids and a wide palpebral fissure. The remainder of the examination was normal.

Discussion

Based on the information given, this patient appears to be a good candidate for LASIK. The presence of astigmatism reduces the laser ablation depth by decreasing the spherical equivalent. In future cases, the ablation depth will be determined by the calculation method.

Remember that the width of the astigmatic treatment zone in a conventional treatment with the VISX laser is 4.5 to 5.0 mm, depending on whether the overall treatment zone is 6.0 or 6.5 mm. If the pupil is large and the degree of astigmatism is large, for example, >2 D, nighttime vision issues are possible. The cornea is somewhat flat, so a larger ring is necessary to make an ample size flap. The risk of an inadequately small or free cap is greater when the corneal contour
is quite flat. If the cornea is very flat, for example, keratometry values <39.00 D, and the degree of correction is low, a surface ablation procedure is a consideration. In this case, there is ample tissue, which allows the surgeon the flexibility to choose a 160- or 180-µm plate on the Hansatome. The size of the treatment zone is selected to be slightly larger than the diameter of the scotopic pupil. A slightly deep-set eye would not pose a serious problem, particularly if the lids are lax and the palpebral fissure is wide. However, patients with deep-set eyes will be more challenging for beginning LASIK surgeons.

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm	Flat contour
Plate size	160 or 180 µm	160 or 180 µm	Actual Hansatome flap likely thinner than the plate
Ablation zone	6.5 mm	6.5 mm	6.0-mm pupils
Spherical equivalent	-2.75 D	-3.50 D	Treat cycloplegic refraction
Calculations: sphere in cycloplegic refraction reduced by nomogram adjustment, then enter into VISX laser	-2.75 × 7% = -0.19 -3.75 – (-0.19) = -3.56 -3.56 + 2.00 × 100°	-3.50 × 7% = 0.25 -4.50 + 0.25 = -4.25 -4.25 + 2.00 × 90° (Use axis from manifest refraction or choose an axis in the middle)	Make sure to reduce the sphere from the cycloplegic refraction by the nomogram adjustment (see discussion on VISX laser in Chapter 7)
Ablation depth Use non-nomogram-adjusted cycloplegic refraction	Using Table 7.4, page 188 = 34 µm Calculation method: 2.75 D × 15 µm/D = 41 µm	Using Table 7.4, page 188 = 42 µm Calculation method: 3.50 D × 15 µm/D = 53 µm	To be conservative, choose the larger of the two values for ablation depth
RSB	550 µm – 160 µm – 41 µm = 349 µm >250 µm	550 µm – 160 µm – 53 = 337 µm >250 µm	RSB > 250 µm; intraoperative measurement is recommended

Take-Home Points

1	Astigmatism reduces the ablation depth by decreasing the value of the spherical equivalent.
2	High astigmatism correction as part of a conventional myopic astigmatic correction may contribute to night vision issues. This is because of the smaller width of the minor axis of the astigmatic treatment zone. For astigmatism >2.00 D, the patient should be advised.
3	A larger microkeratome ring is required if the cornea is flat, and if very flat, avoid using a blade microkeratome. Either use the femtosecond laser for flap creation or do a surface ablation procedure.

CASE 8

A 40-year-old physician has worn RGP hard contact lenses for about 29 years without difficulty. She is very interested in LASIK surgery because she is leaving on a 1-year stay in Nepal, where she will be volunteering in a medical clinic. She sees much better in her contact lenses than in glasses, and desperately wants to avoid the need for contact lenses while she is in remote Nepal.
She was just chosen for this post and is leaving in 2 to 3 weeks and is anxious to proceed with evaluation and the surgery as soon as possible. She has done a lot of research on LASIK and is confident about basic understanding of the risks.

OD – 4.50 20/40 – HCL OD 20/20

OS – 4.50 20/25 – HCL OS 20/20

Uncorrected Va

CF 5′

OD – 3.75 + 0.50 × 90° 20/25

OS – 4.00 + 0.75 × 85° 20/25-

OD – 3.50 + 0.50 × 85° 20/30-

OS – 4.00 + 0.75 × 85° 20/25

OD 43.75 × 177°/44.25 × 87°

OS 43.50 × 180°/44.00 × 90°

Pachymetry

OD 554 µm

OS 557 µm

Topography

Regular with-the-rule astigmatism OU

Scotopic Pupils

OD 5.0 mm

OS 5.0 mm

Additional Examination

Additional examination includes a normal external examination with excellent exposure and tear meniscus, a normal slit-lamp examination, IOP, and fundus examination.

Discussion

Patient desperation and demand for surgery ASAP combined with the inability to adequately follow the patient should raise a red flag that this patient might be a poor candidate for LASIK on the basis of the psychosocial criteria laid out earlier in the basic LASIK section, Chapter 1. There are more red flags that should have been detected. This physician has worn rigid lenses for almost 30 years. The corneas will almost certainly not have enough time to stabilize even if she stops lens wear on the day of examination. She may have an element of irregular astigmatism, which explains why she cannot be refracted to 20/20 or better. While this physician may be familiar with the basic risks of LASIK, she is depending on her refractive surgeon to carefully look at the risks she would face if LASIK were performed under these specific conditions. Despite her desperation, it would be ill-advised to rush into LASIK before her departure. She would be worse off in Nepal with poor uncorrected acuity and inadequate best-corrected acuity.

Treatment Plan

Have the patient stop wearing contact lenses. Refract the patient several days prior to departure and if her acuity is better than with her own glasses, give her a prescription for new spectacles.

Take-Home Points

1	Beware of the patient who is desperate for surgery, overly confident about the risks, and anxious to proceed.
2	Avoid surgery if the patient will not get adequate follow-up care.
3	Allow adequate time for the corneas to stabilize, particularly when the patient cannot be refracted to 20/20 and there is no other cause.

CASE 9

A 51-year-old man with history of myopic astigmatism has had a stable refraction for 1 year. He has a history of contact lens intolerance in the past. He is left eye dominant.

OD – 1.50 + 0.50 × 8° 20/20+

OS – 2.75 20/20 +

Add + 2.00 OU

Uncorrected Va

20/100

20/200

OD – 1.00 + 0.50 × 8° 20/20

OS – 2.75 20/20

OD – 1.25 + 0.25 × 175° 20/15

OS – 2.75 20/15 –

OD 40.00 × 180°/41.50 × 90°

OS 41.00 × 10°/41.75 × 100°

Pachymetry

OD 573 µm

OS 572 µm

Topography

No cone OU

Scotopic Pupil

OD 6.0 mm

OS 6.0 mm

Additional Examination

Deep-set eyes (Case 9, Figs. 1A and B). The examination is otherwise normal.

Discussion

There are several points worth considering in this case. First, at age 51, this patient is highly likely to experience presbyopic symptoms following bilateral treatment for distance. This patient might do very well if only the dominant left eye is treated for distance. The untreated right eye might serve his intermediate and near vision reasonably well. As a rule, patients in this setting are better served with sequential surgery rather than bilateral simultaneous surgery. This allows the patient an opportunity to experience monovision, leaving open the option to subsequently
treat the nondominant eye. A preoperative trial of monovision using a contact lens in the dominant eye is often helpful. Second, the corneal contour is relatively flat. Remember that there is an increased risk of a small flap or free cap when the corneal contour is flat. A larger ring is needed to ensure that the flap will be large enough to accommodate a larger treatment zone. Finally, the periorbital anatomy may pose a problem. Remember to check prominence of the brow, relative height of the palpebral fissure, lid laxity, and degree of enophthalmos in determining whether exposure will be adequate. If exposure is an issue, consider going with a more sturdy speculum such as the Murdock speculum (ASICO AE-183); going without a speculum and the standard ring; using a micro-ring, which has a smaller outer diameter; using a single-piece microkeratome such as the Amadeus or the Nidek, which creates a nasal hinge; or the femtosecond laser which does not depend on the translation of a blade across the cornea. One could also consider a surface ablation procedure. Adequate preoperative sedation can help achieve adequate exposure by relaxing periorbital muscles and reducing blepharospasm.

CASE 9, FIGURE 1 A, B: Deep-set eye. (Courtesy of Robert S. Feder, M.D.)

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm	K < 45.50 D
Plate size	160 µm	160 µm
Ablation zone	6.5 mm	6.5 mm	Pupils <6.5 mm
Spherical equivalent	-1.13 D	-2.75 D
Calculations using nomogram correction	-1.13 D × 7% = -0.08 D -1.25 D + 0.08 D = -1.17 D -1.17 + 0.25 × 175°	-2.75 D × 8% = -0.22 D -2.75 D + 0.22 D = -2.53 D -2.53	Reduce the nomogram adjustment from the sphere in the cycloplegic refraction
Ablation depth	1.13 D × 15 µm/D = 17 µm	2.75 D × 15 µm/D = 41 µm	Use non-nomogramadjusted cycloplegic refraction to calculate ablation depth
RSB	OD: 573 µm – 160 µm – 17 µm = 396 µm OS: 572 µm – 160 µm – 41 µm = 371 µm RSB > 250 µm OU
Special consideration	Because this patient is of presbyopic age, give strong consideration to treating only the dominant left eye. Right eye can always be treated later

Take-Home Points

1	Consider sequential rather than simultaneous treatment if the patient is of presbyopic age and the refractive error of the nondominant eye is suitable for near vision correction.
2	Consider the risk of inadequate flap diameter or free cap if the cornea is flat.
3	Flaps are more difficult to make if the eye is deep set. Remember the various treatment options available in this setting. Discuss the surface ablation option preoperatively.

CASE 10

A 63-year-old man is highly motivated to have refractive surgery to improve his vision. He currently does not wear glasses or contact lenses and functions well. He works full time as an architect. He enjoys fishing and hunting. He drives occasionally and without difficulty during the day but does notice some glare while driving at night.

W	None		Uncorrected Va 20/25+ dist; 14 pt near 20/200 dist; 4 pt near
M	OD – 0.25 + 0.50 × 180° 20/20 OS – 2.00 20/20
C	OD pl + 0.50 × 180° 20/20 OS – 1.75 20/20-
K	OD 42.62 × 179°/42.00 × 89° OS 43.00 × 180°/43.00 × 90°
Pachymetry OD 520 µm OS 520 µm		Topography No evidence of keratoconus		Scotopic Pupils OD 5 mm OS 5 mm

Additional Examination

The patient has excellent exposure. The slit-lamp examination, fundus, and IOP are normal.

Discussion

Occasionally, a presbyopic-age patient will present with naturally occurring monovision who is highly motivated to have refractive surgery. Although his motivation is high, this man currently functions well during work and leisure activities without correction. Although the patient would be willing to have refractive surgery to correct the left eye, surgery would be ill-advised. Because of the loss of near vision postoperatively, this patient would perceive a significant loss of visual function even if the postoperative result were 20/15 OS. While his night driving might improve, he only drives occasionally. His work as an architect would require full-time spectacle use. He would also need reading glasses for fishing. The slight correction in the right eye is too low to treat. This presbyopic patient is not a good candidate for refractive surgery, but might benefit from glasses for night driving.

Take-Home Points

1	Avoid refractive surgery in presbyopic patients who function well without glasses or contact lenses during work and leisure activities.
2	Motivation for refractive surgery does not make a patient a candidate for refractive surgery.
3	The preoperative evaluation is an opportunity to understand the patient’s motivations for surgery, determine if the patient will achieve a net gain from the surgery, and educate the patient.
4	A patient properly advised against surgery can be a potential referral source, while a patient made unhappy with surgery will usually speak negatively about the surgeon and the office.

CASE 11

A 27-year-old woman presented with a history of myopic astigmatism. She states she wants to be able to drive, water-ski, and work at a computer without contact lenses. She has a history of
“lazy eye” OD as a child with no history of strabismus surgery or patching. She also has a history of corneal neovascularization OU. She wears SCL, 2-week disposables, but has tolerated RGP lenses in the past. The patient denies diplopia while wearing contact lenses. Currently, she uses no ocular medications.

OD – 6.25 + 1.00 × 96°20/20

OS – 6.25 + 0.25 × 179°20/30

Uncorrected Va

OD CF

OS CF

OD – 6.00 + 1.25 × 90°20/20+

OS – 7.25 20/15-

OD – 5.75 + 1.00 × 85° 20/15

OS – 6.75 20/15

OD 44.75 × 7°/44.75 × 97°

OS 44.50 × 3°/45.00 × 93°

Pachymetry

OD 549 µm

OS 547 µm

Topography

OD regular astigmatism OS no cone

Scotopic Pupils

OD 7.5 mm

OS 7.5 mm

Additional Examination

There appears to be good exposure. There is a 4 PD esophoria in primary position only. There is also superior and inferior pannus <2.0 mm OU and anterior stromal scarring OD without significant thinning extending <1.5 mm from the superior limbus. The refraction is stable out of contact lenses. Mild blepharitis is present in all four lids.

Discussion

This patient is an acceptable candidate for LASIK surgery. The cornea is thick enough to allow the surgeon to use a 180-µm plate; however, a 160-µm plate would leave more room for retreatment if it became necessary. The esophoria is small; however, if the patient developed a large anisometropia postoperatively, fusion may become more challenging for the patient. The large pupil will require a larger treatment zone. With the VISX laser one could use either a 6.0 or 6.5 treatment zone with the 8.0 mm blend zone. The myopia OS is within the acceptable range for VISX custom OS for high myopia.

The corneal pannus raises an important concern—namely, the risk of intraoperative bleeding. A flap that is large may cut into the vessels resulting in hemorrhage. (See Chapter 1 on ring placement for management of intraoperative hemorrhage.) A smaller flap would help avoid the vessels, but may not accommodate the full treatment zone. Because the keratometry indicates that the cornea is not flat, an 8.5-mm ring would probably be adequate to create the necessary flap size, reducing the risk of bleeding. Ring decentration to avoid isolated vessels risks a significant flap decentration. The femtosecond laser is advantageous in a case like this, because the flap diameter is more predictable. Also the laser process is less likely to induce problematic bleeding into the interface.

The scarring noted in this patient would likely be in the hinge of a superior-hinged flap and not cause a problem. Whenever scarring is present, even if it is peripheral, the surgeon
should attempt to rule out previous herpes simplex disease or other source of chronic keratitis. The blepharitis in this case should be treated and controlled preoperatively and the lids reexamined prior to surgery.

Surgical Plan

	Right Eye	Left Eye	Comments
Ring size	8.5 mm	8.5 mm	Smaller ring to avoid bleeding
Plate size	160 µm	160 µm	More room for retreatment
Ablation zone (VISX laser)	6.5 mm with blend or custom	6.5 mm with blend or custom	Pupils >6.5 mm 6.0 mm zone could also be used
Spherical equivalent	-5.25	-6.75
Calculations with nomogram correction (enter into VISX)	-5.25 × 6% = -0.32 -5.75 + 0.32 = -5.43 -5.43 + 1.00 × 85	-6.75 × 7% = -0.47 -6.75 + 0.47 = -6.28 -6.28	Reduce the sphere of the non-nomogram-adjusted cycloplegic refraction
Ablation depth	5.25 D × 15 µm/D = 79 µm + 8 µm for blend zone = 87 µm	6.75 D × 15 µm/D = 101 µm + 8 µm for blend zone = 109 µm	Remember to add 8 µm additional for blend zone in patient with <10 D; depth with custom may be more
RSB	549 µm – 160 µm – 87 µm = 302 µm	547 µm – 160 µm – 109 µm = 278 µm	RSB > 250 µm OU

Take-Home Points

1	Perform a motility examination routinely. Abnormalities should be explained to the patient. Patients who are asymptomatic in contact lenses should do well unless significant anisometropia or distortion has developed that interferes with fusion. Any potential risks should be explained and documented in the chart.
2	When pannus or neovascularization is present, consider flap diameter and its implications. Balance the need to protect the peripheral cornea with the need to accommodate a large treatment zone. IntraLase, if available, can be helpful.
3	Treat blepharitis preoperatively and examine patient before surgery to be certain that the condition is controlled.

CASE 12

A 23-year-old woman presented for LASIK consultation complaining that her contact lenses had become increasingly uncomfortable and as a result her wear times had been declining. She is an accomplished skier and diver and is unable to wear glasses during these activities. She is in good health. She recently saw her eye doctor and was told her eyes were healthy.

OD – 6.50 + 2.25 × 115°

OS – 5.50 + 2.00 × 85°

Uncorrected Va

CF 5′

OD – 6.25 + 2.00 × 115° 20/20

OS – 5.75 + 2.50 × 80° 20/20

OD – 6.75 + 2.30 × 120°

OS – 5.71 + 2.45 × 84°

OD – 6.50 + 2.25 × 120° 20/20

OS – 5.75 + 2.50 × 85° 20/20

OD 43.00 × 35°/45.75 × 125°

OS 42.75 × 175°/45.50 × 85°

Pachymetry

OD 546 µm

OS 548 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 8.7 mm

OS 8.8 mm

Additional Examination

The external examination was normal, revealing excellent exposure. The tear function was normal. The slit-lamp examination was unremarkable. The IOP was 12 mmHg OU and the fundus was normal OU. WaveScan measurement showed 9.2% HOA and RMS 7.64 OD; and 3.4% HOA and RMS 5.29 OS.

Discussion

Review of old records revealed refractive stability for at least 2 years. She had a relatively high RMS (see discussion of custom VISX in Chapter 7) and had pupils that put her into a high-risk category for night vision complaints when combined with her refractive error. After consultation regarding the options, the patient elected to undergo CustomVue LASIK with IntraLase.

The manifest and WaveScan refractions were well matched so no physician adjustment was used. The high RMS value does not influence the treatment plan in this patient. Clinically, any adjustments are based on comparisons of manifest, cycloplegic, and WaveScan refractions.

The flaps and ablations were well centered, and surgery was uncomplicated. The surgeon needs to remember that the clinical situation may vary depending on the method of flap creation. In this case, the IntraLase femtosecond laser was used to create the flap. Rarely when using the IntraLase, a period of waiting is required until the intrastromal gas dissipates enough to allow the tracker to recognize the pupil. If a significant amount of opaque bubble layer is obscuring the view of the pupil, then it is best not to lift the flap immediately, but to instead wait until the gas dissipates. At the 3-month postoperative visit, the patient had a UCVA of 20/15 with plano refraction OU. The patient had no complaints of nighttime glare or haloes.

Take-Home Points

1	The CustomVue platform allows for adjustment of the treatment zone for patients with large pupils. Some surgeons use the largest feasible treatment zone regardless of pupil size.
2	The CustomVue treatment reduces the risk of night vision problems for patients at risk for such problems or in patients who would be bothered by these symptoms. It induces less new HOAs than many other excimer lasers.

CASE 13

A 32-year-old woman presents for LASIK consultation with the hopes of being less dependent on her glasses. She does not wear contact lenses.

OD – 4.50 20/20-

OS – 4.50 20/20-

Uncorrected Va

CF 5′

OD – 4.75 + 0.75 × 87° 20/15

OS – 4.50 + 0.50 × 85° 20/15-

OD – 4.50 + 0.75 × 85° 20/15-

OS – 4.25 + 0.50 × 85° 20/15

OD 46.75 × 177°/47.25 × 87°

OS 46.50 × 180°/47.00 × 90°

Pachymetry

OD 504 µm

OS 507 µm

Topography

Regular with-the-rule astigmatism OU

Scotopic Pupils

OD 7.5 mm

OS 7.5 mm

Additional Examination

The external examination reveals excellent exposure with a corneal diameter of 10 mm (Case 13, Fig. 1). The slit-lamp examination shows a clear cornea and the anterior chamber is deep and quiet. The lens appears normal and there is no cataract. The IOP and fundus examinations are normal.

CASE 13, FIGURE 1 Small corneal diameter. (Courtesy of Robert S. Feder, M.D.)

Discussion

The important findings in this case are the small cornea with relatively steep curvature. The corneas are rather thin and the pupil is large. The key decision is the recognition that the use of a mechanical microkeratome might be problematic. The flap must be large enough to accommodate a large treatment zone, yet not so large that it extends into the limbus. One could consider using a small ring diameter for the microkeratome to keep the flap from being too large. However, with only slight flap decentration, there is a significant risk of limbal invasion and hemorrhage, because the cornea is small and steep. Other options are probably safer. The most conservative refractive procedure would be PRK in which there is no flap-related risk. A large zone with an added blend could be used and excellent centration should not be difficult to achieve. The patient would need to understand the advantages and disadvantages of sequential and simultaneous surgery.

Another option to consider would be to use the femtosecond laser to make the flap. Remember that the flap diameter with this laser is not dependent on corneal curvature and the diameter can be preset. In addition, with this patient’s thin cornea, the laser would provide more control over the actual flap thickness. Centration is a concern, however. If the applanation lens was not well centered and the cursor was used to center the ablation, the resultant flap might be too small to accommodate the entire ablation. If the flap edges were too close to the limbus, limbal bleeding might occur or air bubbles might extend into the anterior chamber. Despite these possible risks, the femtosecond laser, if available, would be a much better choice than a microkeratome for flap creation.

Surgical Plan
	Right Eye	Left Eye	Comments
The patient opts for PRK OU
Ablation zone	6.5 mm with blend	6.5 mm with blend	VISX STAR S4 laser
No nomogram correction for PRK (enter into VISX)	-4.50 + 0.75 × 85°	-4.25 + 0.50 × 85°
Ablation depth	4.13 D × 15 µm/D = 62 µm + 8 µm = 70 µm	60 µm + 8 µm = 68 µm	Discuss the risk of haze and the need for topical steroids postoperatively
RSB	504 µm -70 µm = 434 µm 434 µm	507 µm – 68 µm = 439 µm 439 µm

Take-Home Points

1	Recognize the special challenge posed by the patient with microcornea.
2	PRK remains an important keratorefractive option in selected cases.
3	The femtosecond laser is safer than the microkeratome in the patient with a small, steep cornea because it offers more control over the flap diameter.

CASE 14

A healthy 31-year-old woman with no significant past medical history had previously worn soft contact lenses for 2 years. She has not worn lenses for 1 month and presents for LASIK consultation.

OD – 5.50 + 1.00 × 93° 20/15-

OS – 4.50 + 0.50 × 75° 20/15

Uncorrected Va

20/400

OD – 5.00 + 1.00 × 90° 20/15

OS – 4.50 + 0.50 × 75° 20/15

OD – 5.00 + 1.00 × 90° 20/15

OS – 4.25 + 0.75 × 65° 20/15

OD 42.00 × 180°/745.50 × 90°

OS 42.25 × 180°/45.50 × 90°

Pachymetry

OD 528 µm

OS 537 µm

Topography

OD + 3.5 D at 94° regular OS +3.0 D at 89° regular

Scotopic Pupils

OD 7.5 mm

OS 7.0 mm

Additional Examination

There is excellent exposure and the examination is normal except for mild blepharitis and moderate acne rosacea.

Discussion

There are several items of note on the examination. First is the pupil diameter. While some believe pupil size and night vision are not related, many surgeons believe that the treatment diameter should be larger than the pupil size measured in the dark. In this case, the VISX laser would treat out to 8.0 mm if a blend zone were to be used. With CustomVue LASIK, the treatment zone could be expanded further if desired. Second, notice that there is substantially more with-the-rule astigmatism on topography and with keratometry than is seen in the cycloplegic refraction. How is this possible? More than likely there is lenticular astigmatism that cancels out some of the corneal astigmatism. If this patient requires cataract surgery in the future, untreated corneal astigmatism may be unmasked. Never treat the astigmatism from keratometry or topography. Some surgeons will choose to use the axis of astigmatism in the manifest refraction, while some will choose an axis midway between the cycloplegic and manifest refractions. Finally, the acne rosacea should be treated with a course of doxycycline, provided the patient is not allergic. She should be warned about sun sensitivity, yeast vaginitis, reduction in the effectiveness of oral contraceptives, and risk to the baby if she becomes pregnant. Also it is important to treat significant blepharitis prior to laser surgery.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm
Plate size	160 µm	160 µm	Actual Hansatome flap often thinner than the plate
Ablation zone	6.5 mm with blend or custom	6.5 mm with blend or custom	Pupils >6.5 mm 6.0 mm with blend can also be used
Spherical equivalent (SE)	-4.50 D	-3.87 D
Calculations with nomogram correction (enter into VISX)	-4.50 D × 6% = 0.27 D -5.00 + 0.27 = -4.73 -4.73 + 1.00 × 090	-3.87 D × 6% = 0.23 D -4.25 + 0.23 = -4.02 -4.02 + 0.75 × 065	Reduce sphere of cycloplegic refraction by the calculated nomogram adjustment
Ablation depth	4.50 D × 15 µm/D = 68 µm+ 8 µm blend = 76 µm	3.87 D × 15 µm/D = 58 µm + 8 µm blend = 66 µm	Calculate ablation depth using the non-nomogram-adjusted SE
RSB	528 µm – 160 µm – 76 µm = 292 µm >250 µm	537 µm – 160 µm – 66 µm = 311 µm >250 µm	Intraoperative pachymetry is the most accurate way to determine RSB

Take-Home Points

1	A large treatment zone is preferable when the pupil diameter is large. However, some surgeons routinely use the largest zone that anatomical constraints will allow regardless of pupil size.
2	It is worthwhile to note disparities between refractive astigmatism and corneal astigmatism measured with topography and keratometry, but base the treatment on the refractive astigmatism.
3	Treat blepharitis and rosacea prior to surgery.

CASE 15

A 27-year-old Asian woman was interested in refractive surgery because she could not see well in glasses and was increasingly uncomfortable in contact lenses. She enjoyed scuba diving and had difficulty using contact lenses underwater. She once tried a prescription mask, but it did not work well. She had a long history of high astigmatism just like her father and her correction had been stable for the past 2 years. She had worn contact lenses for 10 years and had been out of them for 3 weeks.

OD -5.00 + 4.75 × 73° 20/20

OS -6.25 + 6.00 × 80° 20/25±

Uncorrected Va

20/80

OD – 5.00 + 4.75 × 75° 20/20

OS – 5.50 + 4.00 × 75° 20/20

OD – 4.75 + 4.75 × 75° 20/15-

OS -4.75 + 4.00 × 80° 20/20

OD 42.62 / 45.75 × 70°

OS 42.62 / 45.75 × 70°

Pachymetry

OD 502 µm

OS 506 µm

Topography

OD See below

OS See below

Scotopic Pupils

OD 7.8 mm

OS 7.6 mm

Dominant Eye

CASE 15, FIGURE 1 A: Pentacam OD 4 maps refractive view. B: Pentacam OD Belin/Ambrosio Enhanced Ectasia view. C: Pentacam OS 4 maps refractive view. D: Pentacam OS Belin/Ambrosio Enhanced Ectasia view.

Additional Examination

The palpebral fissures were small and the lids were somewhat tight. The corneal diameter was 11 mm OU. The IOP was 12 mmHg OU. The slit-lamp and fundus examinations were completely normal.

Discussion

Careful evaluation of corneal topography is essential in a patient with high astigmatism and relatively thin corneas in order to rule out the presence of preexisting ectatic disease (refer to Chapter 2). The power and elevation maps demonstrate high astigmatism, which appears to be regular and symmetrical with none of the topographic findings one might see in FFKC. It is worth noting that the pachymetry maps reveal the thinnest portion of the cornea to be displaced inferotemporally in the right eye (Case 15, Fig. 1A lower left map) and slightly displaced inferotemporally in the left (Case 15, Fig. 1C lower left map). In this patient, with better than 20/20 best-corrected acuity, stable refraction for 2 years, and normal power and elevation maps, the pachymetric findings alone are probably not sufficient for the surgeon to reject this patient as a candidate for refractive surgery. However, a younger patient with more significant borderline topographic findings may naturally progress to FFKC or even manifest ectasia. As always, it is the surgeon’s judgment and responsibility to determine on which patient to operate. The enhanced ectasia views (Case 15, Figs. 1B and D) do not show an abnormal area of elevation, that is, both lower left maps are green. The pachymetric curves follow the mean and standard deviation curves indicating that the corneal pachymetry increases appropriately as one progresses from the thinnest portion of the cornea to the periphery.

Realistic vision expectations should be presented to the patient. The patient’s unaided postoperative acuity often exceeds 20/40, but is not usually 20/20. It is also possible to lose some of the best-corrected acuity. Near vision is often significantly improved even in young patients who suffer from a high preoperative astigmatic correction. This is an unexpected benefit of surgery that patients frequently discover after refractive surgery. It is important to inform the patient with high astigmatism of the increased risk of nighttime vision symptoms. Some would say the large pupil in this case was a further risk, while others would say the pupil size is not relevant.

In this case, custom treatment on the VISX laser was not an option because of the high cylinder, but in general, the iris registration feature available with custom treatment on the VISX Star 4 laser is helpful in aligning astigmatic treatment. Conventional treatment of myopic astigmatism is approved for up to +5.00 D of cylinder. In this patient with thin corneas, tight lids, small palpebral fissure, and a small cornea, PRK seemed to be a better option than LASIK. The femtosecond laser with adjustable flap diameter does allow predictably thin flaps to be made on small thin corneas. Careful consideration must be given to the predicted residual stromal depth if LASIK is performed in this situation. Remember that ablation depth on the VISX laser is calculated using the spherical equivalent so that high astigmatism will reduce the ablation depth related to the myopic portion of the refraction. When the patient is treated with PRK, it is reasonable to give the patient the option of sequential surgery with the nondominant eye first or simultaneous treatment. Some patients want to get the surgery over at one time. They need to be warned that vision will be poor as the healing epithelial defect is approaching fixation.

Treatment

The patient opted for simultaneous PRK, which was performed based on the cycloplegic refraction. A 6.5-mm zone with a blend zone to 8.0 mm was used. A 9.0-mm epithelial defect was created using 20% alcohol applied for 20 seconds. The calculated ablation depth was 44 µm OD and
49 µm OS. Nine months following surgery, the uncorrected acuity was 20/20+ OD and 20/25 OS with a refraction of plano OD and -0.50 + 0.50 × 145 OS. She noted some glare at night, but on balance was quite pleased.

Take-Home Points

1	Careful analysis of corneal topography, power, elevation, and thickness, is especially important in a highly astigmatic patient to rule out signs of preexisting ectasia.
2	Highly astigmatic patients should be presented with realistic vision expectations and warned about possible nighttime visual symptoms.
3	Successful correction of high astigmatism has the potential to improve near as well as distance vision even in a young person.

CASE 16

A 43-year-old woman, with an 8-year history of biopsy-proven sarcoidosis, presents with interest in refractive surgery. She was treated for iritis 3 years ago, but there have been no recent episodes of ocular inflammation since that time. She wore soft contact lenses steadily until 2 years ago, when the lenses became increasingly irritating. She now uses them only for sports and social occasions. Last month the patient contracted the flu that was going around her office, but now feels fully recovered. She occasionally uses an oral decongestant for sinus congestion.

OD – 5.75 20/30-

OS – 5.50 + 1.25 × 86° 20/20-

Uncorrected Va

OD CF 5′

OS CF 5′

OD – 5.50 + 0.50 × 65° 20/20+

OS – 5.25 + 1.00 × 92° 20/15-

OD – 5.25 + 0.75 × 75° 20/20+

OS – 5.25 + 1.25 × 92° 20/15-

OD 43.12 × 175°/44.00 × 85°

OS 42.62 × 180°/43.75 × 90°

Pachymetry

OD 550µ m

OS 550 µm

Topography

No cone OU

Scotopic Pupils

OD 6.5 mm

OS 7.0 mm

Additional Examination

There is excellent exposure with a wide palpebral fissure, prominent globes, and lax lids. There is punctate fluorescein staining inferiorly on the cornea of each eye. The anterior segment, IOP, and fundus examinations are otherwise normal.

Discussion

The refractive surgery evaluation should always include the patient’s past medical and ophthalmologic history. Both may impact the decision to perform LASIK. In this case, the patient has sarcoidosis. There have been no recent episodes of iritis and the fundus examination is normal, however, the patient has become contact lens intolerant. Patients often do not offer
a history of dry eye even when specifically asked. The clinician must discern whether tear deficiency is present and whether it might affect the surgical outcome. Several of the factors in this case should signal a potential problem with tear function postoperatively. First, sarcoidosis can cause reduction in lacrimal gland tear production. This may have been a factor causing her contact lens intolerance. Second, tear deficiency is more common in middleaged and older women. Third, she is using oral decongestants, which can dry the mucous membranes. The history of the flu might suggest that the consultation is taking place during winter when the ambient humidity is decreased. Next, the wide fissure and prominent globes will undoubtedly increase the likelihood of evaporation from the ocular surface. Finally, the patient works as a copyeditor, requiring her to read all day, further drying the eyes due to exposure.

In short, this patient has many risk factors for dry eye and potential for problems postoperatively. Add to these factors the neurotrophic corneal changes that can result from severing the corneal nerves during flap creation, and the potential for protracted surface irregularity becomes clear. Further evaluation is important in this case. The risk of a postoperative surface abnormality must be explained to the patient. It is prudent to document this in the chart.

The Schirmer’s test is part of the dry eye evaluation, but it is not the only determinant that should be used. The presence of symptoms particularly at the end of the day, injection of the bulbar conjunctiva within the palpebral fissure, mucous discharge, debris in the tear film, a decreased tear meniscus, and punctate fluorescein staining on the cornea and the conjunctiva are all important factors. Clinical judgment is necessary to determine whether a tear deficiency state can be adequately controlled preoperatively. If various treatment regimens such as tear supplements, topical cyclosporine, punctal plugs, humidifiers, and adequate oral hydration successfully reverse the signs and symptoms of dry eye, it may then be safe to proceed with surgery. Remember that a patient with evaporative dry eye due to exposure or poor blink may not respond to tear supplements or plugs as well as the patient with reduced tear production.

Given this patient’s presbyopic age and profession, it is important to discuss the need for reading glasses or monovision correction. If monovision is considered, remember to try this option in contact lenses preoperatively. The nondominant eye is usually the near eye.

Surgical Plan
	Right Eye	Left Eye	Comments
Considerations	Evaluate for dry eye, consider punctal plugs or other measures, and reevaluate. Proceed only if surface is healthy
Ring size	9.5 mm	9.5 mm	Hansatome
Plate size	160 or 180 µm	160 or 180 µm	Actual flap thickness may be thinner or thicker
Ablation zone	6.0 or 6.5 mm with blend or custom	6.0 or 6.5 mm with blend or custom	VISX STAR S4 Pupils >6.5 mm
Spherical equivalent	-4.88 D	-4.63 D
Calculations using nomogram adjustment (enter into VISX laser)	4.88 × 8% = 0.39 -5.25 + 0.39 = -4.86 -4.86 + 0.75 × 75°	4.63 × 8% = 0.37 -5.25 + 0.36 = -4.89 -4.89 + 1.25 × 92°	Some surgeons use cylinder axis from cycloplegic refraction, some use an axis midway between C and M, some use the axis of the M
Ablation depth	4.88 D × 15 µm/D (Use 12 µm/D for a 6.0 mm ablation zone) = 73 µm + 8 µm (for blend) = 81 µm	4.63 D × 15 µm/D (Use 12 µm/D for a 6.0 mm ablation zone) = 70 µm + 8 µm (for blend) = 78 µm	Use non-nomogram-adjusted SE to calculate ablation depth
RSB Intraoperative pachymetry is recommended for RSB calculation	550 µm – 160 µm -81µm = 309 µm >250 µm	550 µm – 160 µm – 78 µm = 302 µm >250 µm	If Hansatome flap is thinner than 160 µm, the RSB will be greater

Take-Home Points

1	Complete past medical and ocular history is an important part of the preoperative evaluation.
2	Be suspicious for a tear deficiency condition and evaluate properly. Treat the dry eye and reevaluate. Operate only if the surface condition can be normalized. Remember that even if it can, the patient may still experience dry eye symptoms for months or years after surgery.
3	Discuss this condition with the patient and document the discussion in the chart.

CASE 17

A 58-year-old woman presents for LASIK consultation, expressing a goal of reducing her dependence on glasses and contact lenses. She wore monovision in contact lenses with the left eye being the near eye. She cannot remember what the monovision correction in the left eye was or where she got the lens. She has not had a problem with dry eye and wears contact lenses comfortably. She has been diagnosed as a glaucoma suspect and uses timolol 0.5% gel-forming solution each morning in both eyes. She was recently evaluated for a thyroid disorder and the laboratory results were normal. She attended her son’s graduation from college 3 weeks ago in Arizona and had no problem with her eyes.

OD – 6.50 + 1.25 × 4° 20/25-

OS – 6.25 + 0.75 × 103° 20/30-

Uncorrected Va

CF 5′

OD – 5.25 + 1.00 × 12° 20/15-

OS – 6.00 + 1.50 × 128° 20/15

OD – 5.00 + 1.00 × 13° 20/15-

OS – 5.75 +1.50 × 130° 20/20±

OD 43.87 × 175°/44.00 × 85°

OS 43.87 × 20°/44.75 × 110°

Pachymetry

OD 506 µm

OS 508 µm

Topography Regular with-the-rule astigmatism OU

Scotopic Pupils

OD 6.5 mm

OS 7.0 mm

Additional Examination

Additional examination reveals an ample tear meniscus without punctate fluorescein staining on the cornea. Upper lid retraction with lagophthalmos was noted primarily OD. The motility
function was normal. The slit-lamp examination was normal. The IOP was 20 mmHg by applanation OU. The cup-to-disc ratio was 0.3 OU and the rest of the fundus examination was normal. Old records were obtained and IOPs had been measured in the high 20s by applanation. Visual fields were obtained and were normal. Stereo disc photographs were obtained for baseline.

Discussion

Monovision should only be considered in presbyopic patients. Before surgery, patients who have never used monovision should have a contact lens trial. This should include both work and leisure activities. If the patient cannot tolerate contact lenses, single-vision monovision spectacles can be prescribed. If contact lens monovision was successful in the past, try to obtain the contact lens prescription. It is important to know how old the patient was at the time of success with monovision and how large a difference was tolerated.

A careful motility examination should be performed prior to surgery. Monovision can disrupt fusion and cause decompensation of a phoria and possible diplopia. Monovision can also have a negative impact on night vision due to defocus in the nondominant eye. This, however, can be corrected with spectacles. The possible negative effect of monovision on night vision should be discussed preoperatively.

Regression of a myopic correction in one eye can result in a form of monovision that the presbyopic patient might find desirable. If monovision correction fails, enhancement surgery can correct the problem. Careful planning before surgery can avoid a failure. CustomVue LASIK (VISX) cannot be performed on the undercorrected eye because the difference between the required treatment and the refraction will be too large. While unilateral custom treatment is usually not recommended when bilateral surgery is being performed, it is not unreasonable to use custom treatment in the distance eye.

This patient was found to have elevated IOP on examinations before the LASIK evaluation. She has thin corneas, so these IOP measurements are significant. However, there was no evidence of glaucomatous nerve damage. The elevated IOP occurring during flap creation would be unlikely to damage a nerve with a 0.3 cup-to-disc ratio. Baseline stereo disc photographs and fields are essential in a case like this, because accurate IOP measurements cannot be made after myopic LASIK. Topical brimonidine (e.g., Alphagan) should be avoided, because it can increase the likelihood of flap displacement.

Women over the age of 50 years are the most likely to develop problems with tear deficiency following LASIK surgery. Tear function should be carefully evaluated in this group, particularly. Lid retraction and lagophthalmos can increase evaporation and complicate a tear deficiency state. Surgery performed in a season or geographic area in which higher ambient humidity is present may be an advantage for patient at risk for dry eye after surgery.

Surgical Plan
	Right Eye	Left Eye	Comments
IntraLase flap diameter	9.0 mm	9.0 mm	Larger flap diameter in case retreatment needed
IntraLase flap thickness (actual flap thickness variance less with laser than microkeratome)	110 µm	110 µm	IntraLase usually creates a flap not greater than 120 µm when set at 110 µm; preferred for patient with thin cornea
Ablation zone	6.5 mm with blend (6.0 mm with blend is an option to conserve tissue)	6.5 mm with blend (6.0 mm with blend is an option to conserve tissue)	VISX STAR S4
Calculations with nomogram correction (enter into VISX)	-4.50 D × 9% = 0.41 -5.00 + 0.41 = -4.59 -4.59 + 1.00 × 13°	-3.00 D × 9% = 0.27 -3.75 + 0.27 = -3.48 -3.48 + 1.50 × 130°	Myopic sphere OS is reduced by 2.00 D to achieve monovision
Ablation depth	4.50 D × 15 µm/D = 68 µm	3.00 D × 15 µm/D = 45 µm
RSB	68 µm + 8 µm blend = 76 µm 506 µm – 120 µm – 76 µm = 310 µm >250 µm	45 µm + 8 µm blend = 53 µm 508 µm – 120 µm – 53 µm = 335 µm >250 µm	Especially important to measure the bed thickness to be certain adequate room for ablation

Take-Home Points

1	Monovision treatment is good for presbyopic patients who have previously been successful with monovision. The potential impact on fusion and night vision should be explained preoperatively.
2	A glaucoma suspect patient may have LASIK, but baseline fields and stereo disc photos are important to establish a baseline. IOP measurements are inaccurate after myopic LASIK.
3	Postoperative dry eye is a concern, particularly in women over 50 years of age. Increased tear evaporation associated with lid retraction, lagophthalmos, and low ambient humidity can increase the risk of postoperative dry eye symptoms.

CASE 18

A 47-year-old woman with a history of myopic astigmatism presents for LASIK consultation. Her refraction has remained stable for over 1 year. She has worn RGPCLs for more than 25 years. She is taking bupropion HCl (Wellbutrin) and sertraline HCl (Zoloft). She is currently not using any eyedrops.

OD – 5.25 + 2.00 × 98° 20/25

OS – 5.25 + 2.25 × 67° 20/30-

Uncorrected Va

OD CF

OS CF

OD – 5.50 + 2.00 × 100° 20/20-

OS – 5.25 + 2.00 × 75° 20/20-

OD – 5.25 + 2.25 × 90° 20/15-

OS – 5.25 + 2.25 × 70° 20/20+

OD 45.62 × 175°/48.25 × 85°

OS 46.00 × 170°/47.00 × 80°

Pachymetry

OD 489 µm

OS 495 µm

Topography

No cone

Scotopic Pupils

OD 5.0 mm

OS 5.0 mm

Additional Examination

The IOP by applanation is 16 mmHg in both eyes. On fundus examination, the patient was found to have prominent bilateral optic disc drusen. Visual fields are shown in Case 18, Figures 1A and B.

CASE 18, FIGURE 1 A: Visual field OD. B: Visual field OS. (Courtesy of Robert S. Feder, M.D.)

Discussion

Optic disc drusen may be associated with optic nerve dysfunction. When there is a question of optic nerve dysfunction, always get a baseline visual field to document a possible preoperative field defect. The preoperative fields in each eye appear in Case 18, Figures 1A and B. This patient did have an inferior arcuate defect in the left eye and a subtle inferonasal defect in the right. It is not known with certainty the effect IOP elevation might have on the optic nerve during flap creation. Therefore, it is prudent to discuss this with the patient and the option of an alternative refractive procedure including a surface ablation procedure.

This patient has thinner than average corneas. Some surgeons choose not to perform keratorefractive surgery when the central corneal thickness is <500 µm and some choose to avoid keratorefractive surgery when the RSB will be <50% of the preoperative thickness. Some surgeons will not do LASIK surgery if the RSB is <300 µm, while others will use 250-µm as their minimum RSB. When the cornea is thin relative to the degree of treatment required, it is important to carefully explain the risk of ectasia. It is also important to explain the limitations on retreatment should this become necessary. In this case, the moderate astigmatism will reduce the amount of tissue ablation required. The small pupil will for some surgeons allow a smaller treatment zone, which will also reduce the amount of ablation. Choosing a thinner plate will likely ensure a thinner flap, although thin flaps often occur in thin corneas. Using very thin plates in thin corneas may result in unacceptably thin or even shredded flaps. The variance of flap thickness is less with the femtosecond laser, which can help the surgeon make a flap that is neither too thick nor too thin. However, the suction ring is generally applied for a longer time with the laser than with a mechanical microkeratome. Finally, when LASIK is performed on a patient with a thin cornea, measuring the stromal bed with ultrasonic pachymetry and subtracting this value from the central corneal thickness measured at the time of surgery is necessary to determine the actual flap thickness.

A surface ablation procedure is a preferable option here because the cornea is thin, there is optic nerve dysfunction, which potentially could be affected by the increased IOP during LASIK, and the ablation depth is only 50 µm, which would limit the risk of haze. If LASIK was to be considered in this case, it would be wise to get a neuro-ophthalmology consultation to assess the potential effect of the procedure on the nerve function, discuss the added risk with the patient, and make certain this is documented in the chart. Some surgeons avoid refractive surgery on patients with significant visual field deficits.

Finally, when performing surface ablation or LASIK, remember to mark the patient at the slit lamp, when astigmatism is present, in order to identify and compensate for cyclotorsion.

This patient had bilateral PRK OU and the 3-year postoperative visual acuity was 20/20 OU with no progression of visual field defects.

Surgical Plan: LASIK and PRK
	Right Eye	Left Eye	Comments
Ring size	N/A for PRK 8.5 mm for LASIK	N/A for PRK 8.5 mm for LASIK	PRK requires 7.0-mm epithelial debridement
Ablation zone	6.0 mm	6.0 mm	Pupils <6.5 mm
Spherical equivalent	-4.125	-4.125
Calculations for LASIK with nomogram correction (enter into VISX)	4.125 × 8% = 0.33 -5.25-0.33 = -4.92 -4.92 + 2.25 × 90°	4.125 × 8% = 0.33 -5.25-0.33 = -4.92 -4.92 + 2.25 × 70°	Make sure to subtract corrected values from sphere of cycloplegic refraction
For PRK (enter cycloplegic refraction into VISX)	-5.25 + 2.25 × 90°	-5.25 + 2.25 × 70°	No need for nomogram correction if doing PRK
Ablation depth	4.125 D × 12 µm/D = 50 µm	4.125 D × 12 µm/D = 50 µm	No nomogram adjustment for PRK. Always use non-nomogram-adjusted cycloplegic refraction to calculate ablation depth for LASIK
Plate size for LASIK	160 µm	160 µm	If flap too thin on first eye, increase plate thickness or change blade for second eye
RSB (LASIK)	489 µm – 50 µm – 160 µm = 279 µm	495 µm – 50 µm – 160 µm = 285 µm	>250 µm

Take-Home Points

1	Patients with abnormal optic discs, including cupping or disc drusen, require preoperative evaluation, including baseline visual fields.
2	High IOP, which occurs during flap creation, may be undesirable in a patient with optic nerve dysfunction.
3	Thinner flaps result when creating microkeratome flaps on thin corneas.
4	PRK is the preferable keratorefractive option when the cornea is thin or increased IOP is undesirable.
5	In addition to the general risks of refractive surgery, always discuss those specific risks that are unique to the individual patient and document the discussion in the record.

CASE 19

A 35-year-old neurologist presents for LASIK consultation. He enjoys all water sports and is a self-proclaimed “surfer in exile.” He wishes to be less dependent on glasses and contact lenses and has worn soft lenses for 15 years. He is in good health and is on no medications. His family history is noncontributory. He mentioned that 6 years ago an eye doctor noted disc asymmetry. Since that time he has received eye care from an optometrist who supplies his contact lenses.

OD – 5.50 20/25+

OS – 6.50 20/25-

Uncorrected Va

OD CF 5′

OS CF 5′

OD – 5.00 20/20

OS – 6.00 20/20-

OD – 5.25 + 0.50 × 90° 20/15

OS – 6.00 20/15-

OD 43.25 × 180°/44.00 × 90°

OS 43.12 × 30°/44.00 × 120°

Pachymetry

OD 513 µm

OS 512 µm

Topography Regular astigmatism OU

Scotopic Pupils

OD 7.5 mm

OS 7.0 mm

Additional Examination

The external examination was normal with lax lids and a wide palpebral fissure. There was early escape of the pupil response to light OS. Color vision on Ishihara plates was normal in each eye. The slit-lamp examination was entirely normal OU. The IOP was 15 mmHg OD and 14 mmHg OS. The disc photos are shown in Case 19, Figures 1A and B, and the visual fields in Case 19, Figures 2A and B.

CASE 19, FIGURE 1 Optic disc photos: (A) right disc and (B) left disc. (Courtesy of Robert S. Feder, M.D.)

CASE 19, FIGURE 2 Humphrey 24-2 visual field: (A) Visual field OD and (B) Visual field OS. (Courtesy of Robert S. Feder, M.D.)

Discussion

Extensive glaucomatous cupping OS was seen on the disc photos. There is an inferior arcuate field defect OS. The pupillary escape noted OS is another indication of optic nerve dysfunction OS. This patient has normal tension glaucoma. Diurnal pressures were obtained and the maximum measured pressure was 19 mmHg OS. Should refractive surgery be offered to this patient? Several important issues must be carefully considered before answering this question. If LASIK were to be performed, a significant elevation in IOP would be required in order to create a flap. It is possible for further nerve damage to occur during this period. While the pressure elevation associated with the femtosecond laser is somewhat less than with a microkeratome, it is not uncommon for the IntraLase ring to cause a transient loss of vision during flap creation. Further, the suction ring must remain in place on the eye for a longer duration with IntraLase than with the microkeratome. If one were to reject LASIK for this reason, would there be additional risks associated with PRK? Measurement of IOP is not reliable after PRK or LASIK. The actual IOP can be significantly higher than the measured reading. Some advocate measuring the pressure from the peripheral cornea using the TonoPen.

This patient’s large pupil and -6.00 D correction necessitate a large ablation zone with a blend resulting in an ablation significantly >75 µm. This carries an increased risk of postoperative haze. Unless mitomycin-C (MMC) was applied during surgery, the patient would require several months of topical prednisolone 1%. Glaucoma patients are more likely to experience a steroid-induced IOP rise, which might be more difficult to detect postoperatively. If haze were to develop after surgery, visual fields might be less reliable. In short, this patient’s glaucoma may worsen and be more difficult to follow after keratorefractive surgery. As a neurologist, this patient has more insight than the average patient concerning his glaucoma and optic atrophy. Nevertheless, after the risks had been explained, he preferred to have LASIK OD and continue to wear his contact lens OS. He understood that he would no longer have binocular vision in spectacles following surgery. He also understood that if glaucoma developed OD, IOP measurement would be less reliable after LASIK.

Surgical Plan
	Right Eye	Left Eye	Comments
IntraLase diameter	9.5 mm	No treatment	IntraLase preferred to create a reliably thinner flap with less IOP elevation
IntraLase depth	110 µm	None	Usually creates a 120-µm flap
Ablation zone	6.5 mm + blend zone 6.0 mm + blend acceptable	None	VISX STAR S4
Calculations with nomogram correction (enter into VISX)	-5.00 D × 6% = -0.30 D -5.25 + 0.30 D = -4.95 D -4.95 + 0.50 × 90°
Ablation depth	-5.00 D ×15 µm/D = 75 µm
RSB	75 µm + 8 µm = 83 µm 513 µm – 120 µm – 83 µm = 310 µm >250 µm	Intraoperative pachymetry is recommended to determine RSB

Take-Home Points

1	A complete eye examination is an important part of the LASIK evaluation.
2	Keratorefractive surgery may make glaucoma more difficult to manage because IOP measurement is unreliable and PRK haze may make fields unreliable; also, steroid-induced IOP elevation may be difficult to detect.
3	It is possible for IOP rise during flap creation to cause further damage to a nerve with extensive glaucomatous damage.

CASE 20

A 32-year-old man presents for LASIK evaluation. His past medical history is negative, but the past ocular history is significant for a 10-year history of disposable soft contact lens wear. His refraction has been stable for at least the past year. There is no history of prior ocular trauma, infection, or prior surgery. He takes no systemic or ocular medications, and has no known drug allergies.

OD – 4.50 + 0.50 × 90° 20/25+

OS – 4.75 + 0.75 × 90° 20/30

Uncorrected Va

OD 20/400

OS 20/400

OD – 4.75 + 0.50 × 90° 20/20

OS – 5.25 + 0.75 × 85° 20/20

OD – 4.75 + 0.50 × 90° 20/20

OS – 5.25+ 0.75 × 90° 20/20

OD 43.5 × 90°/43.0 × 180°

OS 43.5 × 90°/42.5 × 180°

Pachymetry

OD 475 µm

OS 480 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 6.5 mm

OS 6.0 mm

Additional Examination

The patient does not have deep-set eyes. The palpebral fissure is wide OU. The slit-lamp examination reveals normal corneal structure without evidence of guttata or KC. The lenses are clear, and the IOP is 13 mmHg OU by applanation tonometry. Dilated funduscopic examination is unremarkable. Orbscan evaluation reveals posterior elevations of 28 µm in the right eye and 33 µm in the left eye.

Discussion

With the exception of a thin cornea, this patient has no other contraindications to laser refractive surgery. There are those who believe that a cornea with central thickness of <500 µm is inherently abnormal. Even with an estimated RSB of 270 µm, such as in this case, a better solution may be surface ablation. If the refractive error were significantly higher, a phakic IOL could be considered.

Surface ablation may have a higher risk of inducing corneal haze in patients who have an ablation depth of 75 µm or greater. The prophylactic use of MMC 0.02%, using the proscribed protocol (refer to Chapter 13), may help prevent such an outcome. In this patient, after careful discussion and informed consent regarding the use of MMC, surface ablation with MMC was performed.

When using MMC in the context of refractive surgery, several considerations are important. First and foremost is the accurate compounding of MMC. Since there is a fairly narrow therapeutic window, it is imperative that the correct concentration be used. In most series to date, 0.02% (0.2 mg/mL) of MMC is used.

When planning the entered refraction into the laser, it is important to reduce the spherical correction by approximately 10% in order to compensate for the effect of MMC in corneal wound healing, which may result in postoperative hyperopia. (See Chapter 13 for discussion on nomogram adjustment by age and refractive error.) A postulated mechanism for this is that MMC may prevent the compensatory wound healing that typically reverses the initial hyperopic “overshoot’ after myopic surface ablation.

Another important concept is the meticulous adherence to the established protocol for the use of MMC. By doing so, the possible complication rate is dramatically reduced. This involves limiting the exposure of MMC to the central cornea, and away from the limbus, stem cells, sclera, and fornices. This is best accomplished by the use of a corneal light shield, a 6- to 8-mm disk-shaped Merocel sponge. Careful irrigation of any excess MMC from the surface of the eye with 30 mL of balanced salt solution (BSS) will also help reduce the likelihood of complications.

A bandage contact lens is placed on the eye, and topical antibiotics and steroids are used qid for 1 week. Steroids are then tapered over the subsequent 3 weeks. With this technique, reepithelialization is not delayed, and is usually completed within 3 to 5 days, similar to cases of surface ablation in which MMC is not used.

Take-Home Points

1	Avoid LASIK on very thin corneas. Surface ablation or phakic IOL insertion may be a better long-term solution.
2	Consider MMC prophylaxis in higher myopic surface ablations, when the estimated ablation depth is 75 µm or greater.
3	Follow the MMC protocol for preparation and application meticulously.
4	Adjust the entered refraction according to the nomogram (see Chapter 13) to take into account the effect of MMC on wound healing.

CASE 21

A 40-year-old woman with congenital nystagmus and mild amblyopia OU presented for LASIK consultation in the hope that the surgery would improve her visual acuity. The patient had become intolerant to the soft daily wear contact lenses she had used for the previous 15 years. Her past ocular history was otherwise noncontributory and her general health was excellent. The risks of LASIK surgery were explained in detail. It was explained that surgery was unlikely to improve her visual acuity beyond what she could do in glasses or contact lenses.

OD – 3.00 + 2.00 × 89° 20/40

OS – 3.25 + 1.75 × 100° 20/40

Uncorrected Va

20/100

20/200

OD – 3.25 + 2.25 × 91° 20/40+2

OS – 3.00 + 2.00 × 95° 20/30-1

OD – 2.22 + 2.19 × 91°

OS – 1.98 + 1.93 × 96°

OD – 2.75 + 2.25 × 90° 20/30-

OS – 2.50 + 2.00 × 95° 20/30-

OD 42.00 × 180°/44.25 × 90°

OS 41.75 × 188°/44.00 × 98°

Pachymetry

OD 550 µm

OS 557 µm

Topography

No cone

Scotopic Pupils

OD 5.9 mm

OS 6.3 mm

Additional Examination

Exposure was excellent. There was no detectable tropia. The slit-lamp examination, IOP, and dilated fundus examination were normal. WaveScan measurement showed HOA 8.8% and RMS 2.88 OD, and HOA 8.8% and RMS 2.89 OS.

Discussion

This case brings up two important issues for discussion. First is amblyopia or reduced best-corrected acuity. The nature of the reduced acuity must be elucidated. LASIK is a surgical procedure designed for a healthy eye. Any corneal abnormality causing reduced acuity would likely lead to an unpredictable result after LASIK surgery and would, therefore, be a contraindication. Decreased acuity due to a potentially progressive cataract would be another contraindication. However, mild amblyopia in an otherwise healthy eye is not a contraindication provided the patient has reasonable expectations. The limitations on postoperative acuity need to be carefully explained and understood before surgery. In most cases, the reduced amblyopic target acuity is easier to achieve with LASIK. If, however, a significant tropia is associated with amblyopia, caution is advised. Improving the unaided acuity may affect suppression and result in diplopia.

The second issue is nystagmus. It is potentially difficult to obtain a WaveScan in a patient with a moving eye. Large-amplitude nystagmus might be difficult for the laser to track and it also may
be difficult to center a microkeratome, because the eye is moving as suction is being applied. Finally, registration could be an issue. It is difficult to mark such a patient at the slit lamp for alignment with the laser. Accurate registration is an important step in any custom LASIK surgery or in conventional surgery to correct significant astigmatism.

In this case, the patient was marked, the WaveScan refraction was double-checked, and the tracker was tested with the patient before any treatment commenced. The flaps and ablations were well-centered and the surgery proceeded without complication.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring diameter	9.5 mm	9.5 mm	Hansatome
Plate thickness	160 µm	160 µm	Usually creates a 120-µm flap
Ablation zone	6.0 mm with transition to 8.0 mm	6.0 mm with transition to 8.0 mm	VISX STAR S4 CustomVue
No nomogram adjustment needed (enter into VISX)	-2.22 + 2.19 × 91° Physician adjustment of -0.50 D -2.72 + 2.19 × 91°	-1.98 + 1.93 × 96° Physician adjustment of -0.50 D -2.48 + 1.93 × 96°	Spherical portion can be adjusted ±0.75 D. In US cylinder, power and axis is fixed
Ablation depth RSB	Low ablation depth with ample corneal thickness. RSB adequate OU	Low ablation depth with ample corneal thickness. RSB adequate OU	Ablation depth is calculated by WaveScan unit

At 2 months postoperatively, the patient had an uncorrected acuity of 20/50 OD and 20/30-2 OS. The manifest refraction was OD -0.50 + 0.25 × 90° and OS +0.50 + 0.25 × 105° with best-corrected visual acuity (BCVA) of 20/30-2 and 20/25-2, respectively. Although the patient still has some residual refractive error, the BCVA showed a one-line improvement over the preoperative BCVA.

Take-Home Points

1	Mild amblyopia, in and of itself, is not a contraindication to LASIK surgery, provided the patient has reasonable expectations.
2	Nystagmus can pose a problem for marking and registration, WaveScan acquisition, microkeratome centration, and laser tracking.
3	The patient should be evaluated before surgery to determine if the laser can track the eyes. A robust tracker can increase the safety of LASIK in the nystagmus patient.

CASE 22

This 34-year-old man with myopic astigmatism desired LASIK so that he could drive, play golf and tennis, and watch TV without glasses. He had no significant ocular history. He admitted to being very squeamish about his eyes, and had some difficulty focusing straight ahead during his LASIK consultation.

OD – 4.75 + 1.50 × 90° 20/20

OS – 5.50 + 1.75 × 90° 20/20

Uncorrected Va

20/400

OD – 5.00 + 1.50 × 90° 20/15

OS – 6.00 + 2.00 × 90° 20/15

OD – 4.75 + 1.75 × 90° 20/20

OS – 5.50 + 1.75 × 90° 20/20

OD 43.50 × 180°/45.50 × 90°

OS 43.75 × 178°/45.75 × 88°

Pachymetry

OD 560 µm

OS 557 µm

Topography

With-the-rule astigmatism OU

Scotopic Pupils

OD 6.0 mm

OS 6.0 mm

Additional Examination

There was nothing unusual about the slit-lamp examination of the anterior segment. His ability to cooperate for the eye examination was suboptimal. He was a “squeezer” who was photophobic and had difficulty maintaining fixation for the examination. There was concern about this patient’s ability to cooperate for the laser ablation, especially maintaining fixation. In addition, he had a moderate amount of astigmatism so proper alignment of the laser on his cornea was critical for effective laser correction.

Discussion

This patient was an acceptable, although not ideal, candidate for LASIK surgery. He had a thick cornea and was expected to have a generous RSB after myopic ablation. The main concern was about his ability to cooperate for the laser ablation. As usual, the 12 and 6 o’clock axes were marked at the slit lamp with a sterile marking pen, prior to bringing the patient into the LASIK suite to be prepped and draped. Despite the availability of the VISX S4 excimer laser tracking system, the Moria suction ring on a low-vacuum setting was used during laser ablation to help stabilize the globe. Proper alignment of the globe was important because of the dangers of a misaligned treatment of moderate astigmatism.

After making the cutting pass on high vacuum with the Moria CB microkeratome, the device was switched to low vacuum. The microkeratome was reversed and removed, but the suction ring remained on the eye. The low-vacuum setting enabled the suction ring to maintain a firm grasp on the globe, but at a much lower and safer level of IOP. While holding the metal suction ring handle with the left hand, the globe could be stabilized while performing the laser ablation. The ablation went smoothly, and the patient felt relieved that the potential fixation problem was overcome by using the low-vacuum technique.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring size	0	0	Moria CB
Microkeratome head	130 µm	130 µm	Typically cuts 160-µm flap
Ablation zone	6.5 mm with blend zone	6.5 mm with blend zone	VISX STAR S4
Cycloplegic Rx	-3.25 – 1.50 × 180°	-3.75 – 1.75 × 180°	Minus cylinder form
Calculations using Dr. Rosenfeld’s nomogram correction (VISX)	-2.93 – 1.50 × 180°	-3.38 – 1.75 × 180°	10% reduction of sphere using the cycloplegic examination in minus cylinder form
Flap thickness	160 µm	160 µm
Ablation depth	56 µm	62 µm
RSB	344 µm	335 µm	>250 µm OU

Take-Home Points

1	The low-vacuum setting on the Moria microkeratome permits exquisite control of the globe during laser ablation.
2	Proper alignment of the axis of astigmatism is critical for treating moderate to high levels of astigmatism.

CASE 23

A 46-year-old dental hygienist with a 30-year history of hard PMMA contact lens wear was seen for refractive consultation. She had early symptoms of presbyopia and had begun to wear near correction over her contact lenses. Her past ocular history was otherwise negative. Her past medical history was significant for medically controlled hypertension.

OD – 6.50 + 0.50 × 72°

OS – 6.00 + 0.50 × 64°

Uncorrected Va

20/400-

OD – 6.75 + 0.50 × 110° 20/20

OS – 6.00 + 1.00 × 70° 20/20 with + 1.25 add → 20/20 near OU

OD – 6.75 + 0.25 × 120° 20/20

OS – 6.00 + 0.75 × 70° 20/20

OD 45.50 × 90°/44.50 × 180°

OS 46.50 × 77°/45.25 × 167°

Pachymetry

OD 500 µm

OS 495 µm

Topography

+0.75 D × 90° OD

+1.00 D × 77° OS

Scotopic Pupils

OD 6.5 mm

OS 6.5 mm

Additional Examination

Her corneas, tear film, lids, and conjunctiva were normal. Her corneal maps were regular without signs of contact lens-induced warpage.

Discussion

This patient was a long-time rigid PMMA contact lens wearer. This type of patient represents a challenge in two ways. First, the surgeon must be sure that there are no signs of contact
lens-induced effects on the cornea. These include contact lens warpage, which can induce irregular astigmatism, masked astigmatism, and/or myopia that is hidden by the flattening effects of the rigid contact lens. The corneal maps must look smooth and regular and the principal astigmatic axes must be 90° apart. The magnitude and direction of the topographic astigmatism should closely match the refractive astigmatism, although there is usually 0.25 to 0.50 D more astigmatism seen on the maps compared to the refraction. Second, patients who are long-time rigid contact lens wearers have higher visual expectations than patients who wear soft lenses or spectacles. The rigid lenses mask any irregular astigmatism on the patient’s cornea and produce an artificially regular surface. These patients should be counseled that their postoperative vision may never be as good as their vision with their rigid lenses.

This patient at age 46 is already experiencing presbyopic symptoms; therefore, careful and complete counseling about presbyopia should be undertaken. Monovision correction for this dental hygienist would be ill-advised because of the effect on stereopsis.

Finally, this patient has thin corneas with a relatively high refractive error. Therefore, the corneas are too thin for LASIK. The risk of haze after surface ablation in this case is significant. This should be discussed with the patient. Consideration of adjunctive MMC treatment would be advisable. The techniques for surface ablation (PRK, Epi-LASIK, and LASEK) should be discussed. See Case 51 to find out what happened in this case.

Surgical Plan
	Right Eye	Left Eye	Comments
Considerations	Do not perform LASIK if the cornea is too thin. Be sure that there are no effects from the rigid contact lens
Ring size	None in PRK	None in PRK	Cornea too thin
Plate size	None in PRK	None in PRK	Cornea too thin
Ablation zone	6.5 mm with blend	6.5 mm with blend	Pupil = 6.5 mm OU
Spherical equivalent	-7.50 D	-6.25 D
Conventional surface treatment based on manifest and cycloplegic refractions Treatment is entered in minus cylinder form	-6.75 + 0.50 D × 110° -6.25 – 0.50 × 20°	-5.75 + 0.75 D × 70° -5.00 – 0.75 × 160°	There is no nomogram adjustment with PRK
Ablation depth	120 µm	98 µm	The Alcon software calculates the ablation depth
RSB	500 µm – 120 µm = 380 µm	495 µm – 98 µm =397 µm

Take-Home Points

1	Be sure the patient stays out of her rigid contact lenses until the refraction and topography become stable. The stable topography should be consistent with the refraction.
2	Warn patients in their mid-40s about the effect of myopic LASIK on presbyopia and discuss treatment options. Avoid monovision in patients who require excellent stereopsis to perform their jobs.
3	Avoid LASIK if the cornea is too thin.

CASE 24

A 46-year-old man presents for LASIK consultation. He is hoping to be less dependent on distance glasses and understands he will need to wear reading glasses. He is not interested in monovision. The patient explains he could never wear contact lenses because he is an intense “eyelid squeezer.’ He has a history of hypertension and hypercholesterolemia. He also has sleep apnea and wears a continuous positive airway pressure (CPAP) mask every night to assist his breathing during sleep (Case 24, Fig. 1).

OD – 8.25 + 1.00 × 72° 20/30+

OS – 6.00 + 0.75 × 77° 20/30-

Uncorrected Va

CF 3′

OD – 7.50 + 1.00 × 85° 20/25-

OS – 5.50 + 0.75 × 85° 20/20-

OD – 7.50 + 1.00 × 90° 20/25+

OS – 5.50 + 0.75 × 85° 20/20-

OD 41.62 × 179°/43.25 × 89°

OS 42.00 × 180°/42.87 × 90°

Pachymetry

OD 556 µm

OS 550 µm

Topography

No evidence of ectasia OU

Scotopic Pupils

OD 6 mm

OS 6 mm

Additional Examination

Intense blepharospasm is noted when attempting tonometry, but IOP is measured and is normal. A 12Δ right exotropia is noted. The slit-lamp and fundus examinations are normal.

CASE 24, FIGURE 1 Donning the CPAP mask risks bumping the eye and displacing the flap. Air flow over the flap may cause excessive dryness. (Courtesy of Robert S. Feder, M.D.)

Discussion

Although this patient is highly motivated to have LASIK surgery, he is a poor candidate. Intense blepharospasm can be associated with an incomplete or partial flap intraoperatively. It can also be associated with a displaced flap postoperatively. In addition, this patient wears a CPAP mask at night (refer to Case 24, Fig. 1). The proximity of the mask edge to the eye may also increase the risk of flap displacement.

While LASIK is a poor choice, a surface ablation procedure is a viable option for this patient. The surgeon must carefully explain how surface ablation is different from LASIK. A patient expecting the rapid visual rehabilitation and minor irritation commonly experienced after LASIK surgery will be disappointed with the increased discomfort and slow return of vision after PRK. With the VISX STAR S4 laser and a 6.5-mm optical zone, the estimated ablation depth would be 105 µm OD and 77 µm OS if the nonadjusted refraction is used for the calculation. Alternatively, a 6.0-mm optical zone with a blend to 8.0 mm could be used to conserve tissue. Many surgeons feel that ablation depths of 75 µm or more are associated with significantly more postoperative haze and recommend using topical MMC 0.2 mg/mL applied to the stromal bed with a 6.0- or 7.0-mm foam corneal protector to reduce the risk of haze. (Refer to Chapter 13 on use of mitomycin- C.) The exact amount of time the MMC is applied varies by the surgeon from 12 seconds to 2 minutes. If MMC is used, it is important to reduce the spherical portion of the treatment by 10% to 12%. It is also important to inform the patient that MMC has not been FDA-approved for this purpose, MMC may permanently affect the healing ability of the cornea, and long-term studies on its use to prevent corneal haze have yet to be done.

Remember to always check the keratometry readings in any high myopia case. To estimate the expected postsurgical corneal curvature, multiply the spherical equivalent of the cycloplegic refraction by 0.7 or 0.8 (depending on how conservative the surgeon is) and subtract the product from the average of the presurgical keratometric values. If the result is <35.00 D, there is an increased risk of poor visual function and keratorefractive surgery may not be advisable. In this case, the result of the curvature calculation is significantly >35.00 D, leaving room for retreatment if necessary. The small risk of postoperative diplopia related to the preexisting exotropia should be discussed. Finally, this presbyopic patient must be educated about monovision and the need for reading glasses if full correction is achieved.

Take-Home Points

1	Blepharospasm is a risk factor for partial or incomplete flap intraoperatively.
2	Wearing a nighttime CPAP mask may increase the risk of both flap displacement and dryness.
3	Surface ablations deeper than 75 µm are more likely to develop stromal haze postoperatively.
4	The use of topical MMC 0.2 mg/mL may reduce the risk of postoperative stromal haze, but requires a 10% to 12% reduction in spherical myopic power. The use of MMC requires significant patient education.
5	Do not forget to calculate the postoperative corneal curvature in any high myopia patient to be certain the new corneal contour will not be <35.00 D, possibly too flat to support good visual function.
6	Warn the patient with a tropia about the possibility of diplopia postoperatively, if the ability to suppress the wandering eye is disturbed.
7	Make sure the myopic patient of presbyopic age being treated in both eyes for distance really understands the impact this will have on unaided near vision.

CASE 25

A 32-year-old man presents for LASIK evaluation. His past medical history is negative. The past ocular history is significant for a 10-year history of disposable soft contact lens wear, but no
history of prior ocular trauma, infection, or prior surgery. He takes no systemic or ocular medications, and has no known drug allergies. His refraction has been stable for more than 1 year.

OD – 4.50 + 0.50 × 90° 20/25

OS – 4.75 + 0.75 × 90° 20/30

Uncorrected Va

20/400

OD – 4.75 + 0.50 × 90° 20/2°

OS – 5.25 + 0.75 × 85° 20/20

OD – 4.75 + 0.50 × 90° 20/20

OS – 5.25 + 0.75 × 90° 20/20

OD 43.00 × 180°/43.50 × 90°

OS 42.50 × 180°/43.50 × 90°

Pachymetry

OD 475 µm

OS 480 µm

Topography

Regular bow-tie OU

Scotopic Pupils

OD 6.5 mm

OS 6.5 mm

Additional Examination

The patient does not have deep-set eyes. The palpebral fissure is wide OU. The slit-lamp examination reveals normal corneas without evidence of guttata or KC. The lenses are clear, and the IOP is 13 mmHg OU by applanation tonometry. The dilated funduscopic examination is unremarkable. Orbscan evaluation reveals posterior elevation of 47 µm in the right eye and 49 µm in the left eye. The anterior elevation, keratometry, and pachymetry maps of the Orbscan are normal. Specifically, there is no inferior steepening on the keratometry map, and although the overall pachymetry is low, there is no focal area of thinning on the pachymetry map, either centrally or inferiorly, corresponding to the area of highest posterior elevation.

Discussion

This patient is a good candidate for laser vision correction by surface ablation (PRK), except for the abnormal posterior elevation on Orbscan (See Chapter 2 on corneal topography). The Orbscan uses a scanning slit to image the cornea, and by compiling the images, it can reconstruct the anterior and posterior curvature of the cornea. Analysis is made with reference to a “best-fit sphere’ and, therefore, any curvature above or below that sphere is given a positive or negative elevation value. Some believe that the earliest corneal changes in ectasia occur in the posterior cornea; therefore, if a patient has significant posterior elevation of the cornea, it may be an early indicator of FFKC. Although no absolutes can be given, it is generally accepted that values above 50 µm (0.050 mm) of posterior elevation are highly suspicious, and values between 40 and 50 µm should at least prompt a discussion with the patient of the potential for ectasia.

Surface ablation techniques may be a safer alternative to LASIK in this setting. Although one cannot unequivocally state that the risk of ectasia after surface ablation is zero, the risk is probably much less than with LASIK. In the setting of high myopia or in cases of higher risk for the development of haze, the judicious use of prophylactic MMC may be beneficial. There are many good reasons to avoid any elective corneal surgery in patients with KC or FFKC. Even a relatively “safer’ procedure such as PRK with MMC is not recommended at this time due to unknown effects of laser ablation on these corneas, and the unknown effect of MMC on keratocytes in patients with KC or FFKC. The procedure has the potential to cause acceleration of the ectatic process.

Take-Home Points

1	Analysis of the posterior corneal surface with the Orbscan may be beneficial in identifying patients with FFKC or KC.
2	Use caution in performing LASIK in patients with posterior elevation above 40 µm.
3	Avoid LASIK in patients with posterior elevation above 50 µm.

CASE 26

A 31-year-old woman with a history of soft contact lens wear for 15 years presents for LASIK consultation. The patient has a history of migraines. There is no history of other eye problems. The patient states she has not needed new glasses in the past year. Medications include Imitrex and Prozac.

OD – 5.75 20/20

OS – 5.75 20/40+ (old R×)

Uncorrected Va

OD CF

OS CF

OD – 6.75 20/20

OS – 6.25 + 1.50 × 35° 20/20-

OD – 6.25 20/15

OS – 6.00 + 1.50 × 45° 20/15-

OD 45.50 × 180°/45.50 × 90°

OS 45.50 × 142°/46.50 × 52°

Pachymetry

OD 529 µm

OS 501 µm

Topography

Preoperative: Case 26 Figures 1, 2, and 3

Scotopic Pupils

OD 6.0 mm

OS 6.0 mm

Additional Examination

After 3 weeks out of contact lenses, the cycloplegic refraction remained stable. IOP and fundus examinations were normal. Corneal topography was obtained at that time. See Case 26, Figures 1 and 2, OD and OS, respectively. Normal band view of OS is seen in Case 26, Figure 3.

Discussion

A critical review of the preoperative topography maps is essentially normal in the right eye (Case 26, Fig. 1); however, the power map of the left eye (Case 26, Fig. 2) in the lower left corner deserves special consideration. Notice the dumbbell appearance and particularly how the superior portion is skewed to the right. Rabinowitz refers to this finding as skewed radial axes and has suggested that a deviation >21 degrees is an important index in screening patients for the diagnosis of KC. Refer to the discussion on corneal topography in Chapter 2. In this patient, the central corneal power value is <47.2 D cutoff described by Rabinowitz, but the Sim-K astigmatism of 1.8 D is >1.5 D index.

Another way to look at this patient is to examine the Orbscan II topography using the normal band scale (Case 26, Fig. 3). This was discussed in the section on topography in Chapter 2. Remember that if orange is present in two maps, surface ablation would be a better option than LASIK, provided the risk of ectasia has been explained. Review of this map shows orange in the posterior elevation map upper right and a small orange spot in the power map on the lower left.

CASE 26, FIGURE 1 Preoperative topography OD. (Courtesy of Robert S. Feder, M.D.)

CASE 26, FIGURE 2 Preoperative topography OS. (Courtesy of Robert S. Feder, M.D.)

The presence of orange in two maps is one indicator of a higher risk of ectasia with LASIK. PRK is the preferable choice provided the patient is informed of the ectasia risk.

Another useful index found on the Orbscan II unit is the posterior elevation difference with best-fit sphere. This value is found when the curser is placed on the highest part of the posterior elevation map. The value in the gray box to the left should ideally be <0.04 mm. In this patient, who was treated prior to our awareness of this index, the value was >0.05 mm. Caution is also recommended when the irregularity at the 3.0-mm zone is ±2.0 D or the irregularity at the 5.0-mm zone is ±2.5 D. A more conservative approach would be to use ±1.5 D at 3.0 mm and ±2.0 D at 5.0 mm. The value in this case is ±2.1 D at both diameters. Finally, if the cornea is >20 µm thinner in the periphery than in the center, the postoperative ectasia risk may be increased. No
set of indices is foolproof in preventing postoperative ectasia. It is recommended that several indices and analyses be used to determine whether a particular patient is suitable for keratorefractive surgery. The risks should be carefully and completely explained to the patient and the discussion should be documented in the chart. Some surgeons have the patient sign the record to acknowledge an understanding of the unique risks in the specific case.

CASE 26, FIGURE 3 Preoperative normal band view OS. (Courtesy of Robert S. Feder, M.D.)

In this case, notice also that there is a significant difference in corneal thickness between the two eyes, with the eye suspicious for FFKC being 28 µm thinner than the fellow eye by ultrasonic pachymetry measurement. The patient is eager to have LASIK surgery in both eyes despite the increased risk of postoperative ectasia in the left eye. The options in this case are to avoid corneal refractive surgery, consider PRK in the left eye, or proceed with LASIK. Because LASIK would involve ablation at a deeper layer of the cornea, PRK would be preferable. Conservative surgeons would avoid surgery particularly in the OS, given a picture suggestive of FFKC.

Surgical Plan: LASIK OD and PRK OS
	Right Eye	Left Eye	Comments
Ring size	8.5 mm	N/A	K > 45.50
Plate size	160 µm	N/A	Usually thinner flap occurs in thin corneas
Ablation zone	6.5 mm (alternatively, a 6.0-zone plus blend)	6.5 mm (alternatively a 6.0-zone plus blend)	Pupils <6.0 mm
Spherical equivalent	-6.25 D	-5.25 D
Calculations with nomogram correction (enter into VISX)	-6.25 × 6% = 0.375 -6.25 + 0.38 =-5.87 -5.87	-6.00 + 1.50 × 45°	Some surgeons prefer to use the axis from the manifest refraction
Ablation depth	6.25 D × 15 µm/D = 94 µm	5.25 D × 15 µm/D = 79 µm	The risk of haze may be increased, due to an ablation depth >75 µm
RSB	529 µm – 160µm – 94 µm = 275 µm >250 µm	501 µm – 79 µm = 422 µm	This patient may require an RSB >300 or more to prevent ectasia

CASE 26, FIGURE 4 Postoperative topography OS. (Courtesy of Robert S. Feder, M.D.)

Postoperatively, this patient achieved an uncorrected acuity of 20/20 OD and 20/30 OS. Her refraction 6 months after surgery was plano OD and -0.50 + 1.50 × 50° 20/25 OS. She is aware that her acuity is better OD, but is overall quite happy with the refractive outcome. The postoperative topography map 6 months after surgery OS is shown in Case 26, Figure 4. The left eye shows further skewing of the radial axes with the development of superotemporal flattening. The posterior float, upper left, is much steeper OS (PRK eye) than it was OD despite the much greater RSB OS. Whether there will be continued progression is not known, but further close follow-up is warranted.

Take-Home Points

1	Reduced best-corrected acuity and significantly decreased central thickness relative to the fellow eye are signs that may be present in association with FFKC.
2	Review preoperative topography carefully for signs of KC or pellucid marginal degeneration (PMD). Different indices provided on most topography units can help determine the presence of subclinical KC, but may not detect PMD.
3	If corneal ectasia is present, the patient should not have corneal refractive surgery. If a patient does not seem to understand the risk that may be present in any case, do not do refractive surgery.
4	In borderline cases, PRK might be a better choice than LASIK to maximize the RSB. If the ablation depth is >75 µm, the use of topical MMC is a consideration to reduce the risk of haze. However, the long-term effects of MMC, particularly in cases such as this are not known.
5	Even when PRK is performed and the RSB is >300 µm, progressive ectasia may occur.

CASE 27

A 35-year-old woman comes in for LASIK consultation. Her husband had successful LASIK surgery 1 year previously and she wondered if she could be a candidate.

She tried contact lenses, but could never wear them comfortably. If she had to, she could see without glasses, but she would get a headache. She wears glasses full time at work and for leisure activities, both for near and distance.

OD + 3.25 20/20-3

OS + 3.50 20/25-

Uncorrected Va

20/30 18 pt

20/80 24 pt

OD + 3.75 20/15

OS + 4.25 + 0.50 × 55° 20/20+

OD + 4.50 20/15

OS + 5.50 + 0.50 × 60° 20/15 slow

OD 43.25 × 15°/44.00 × 105°

OS 43.50 × 12°/44.00 × 102°

Pachymetry

OD 544 µm

OS 537 µm

Topography

Regular with-the-rule astigmatism OU

Scotopic Pupils

OD 5.0 mm

OS 5.0 mm

Additional Examination

The external examination shows good exposure with no evidence of dry eye. The motility examination does not reveal a tropia or phoria. The slit-lamp examination, IOP, and fundus are normal.

Discussion

The key finding in this case is the discrepancy between the spectacle correction and the cycloplegic correction. The difference is +1.25 D OD and over +2.00 D OS. Given this degree of hyperopia, it is not a surprise that she has difficulty functioning without correction despite her pre-presbyopic age. The question is on which refraction should the treatment be based? If you treat on the cycloplegic refraction, she will be quite myopic initially and this might be difficult for her to tolerate. Further, adding the required overcorrection of 25% of the spherical equivalent (see the hyperopia nomogram, Table 7.2, page 77, which is based on age and spherical equivalent) to the sphere portion of the treatment boosts the sphere to +7.19 D. This is well above the approved range for hyperopia with the VISX STAR S4. On the other hand, treating on the manifest refraction will leave her significantly undercorrected and symptomatic as she gets older. What to do? The first step with this easygoing individual is to explain the situation. Good communication, including the patient in the decision-making process, is especially helpful in situations such as this. The best approach is to gradually increase the glasses correction, allowing her sufficient time to adapt to a spectacle correction that is close to the cycloplegic refraction. This process may occur over several weeks or even months; therefore, patience on the part of the doctor and the patient will be required.

Once the patient is comfortable with the full correction, the question of how to deal with the large degree of hyperopia moves to the forefront. Treatment of the right eye is within the approved parameters for LASIK, while the left eye exceeds the upper limit. Because she cannot wear a contact lens, both eyes must be corrected. The options for the left eye include insertion of a phakic IOL (not yet approved in the United States for hyperopia) and clear lens exchange with insertion of an accommodating IOL or multifocal implant. The multifocal IOL is a less desirable option when used as a unilateral treatment. Another option is PRK. PRK for hyperopia does not require a nomogram adjustment and the treatment would, therefore, be within the approved range. It has the advantage of not being an intraocular procedure, but the disadvantage of postoperative discomfort and slower visual rehabilitation. Finally, with large hyperopic keratorefractive procedures, it is important to apply the keratometric conversion factor adding the spherical equivalent in diopters to the preoperative average keratometry value to confirm that the proposed treatment will not induce corneal steepening >50.00 D.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring size	9.5 mm	None for PRK
Plate size	160 µm	None for PRK	Hansatome flap usually thinner than 160 µm
Ablation zone	9.0 mm	9.0 mm	Hyperopic protocol
Calculations with nomogram correction (enter into VISX)	+4.00 × 25% = 1.00 +4.00 + 1.00 = +5.00 +5.00 D	+5.50 + 0.50 × 60°	No nomogram adjustment for PRK OS
Ablation depth	5 D × 8 µm/D = 40 µm	5.75 D × 8 µm/D = 46 µm
RSB	544 µm – 160 µm – 40 µm = 344 µm >250 µm	537 µm – 160 µm – 46 µm = 331 µm >250 µm	Hyperopic ablation is not deepest centrally, so RSB is significantly >250 µm

Take-Home Points

1	If the manifest and cycloplegic refractions are significantly different, explain this to the patient and help the patient adapt to a correction similar to the cycloplegic before surgery.
2	BPRK on the VISX STAR S4 does not require a nomogram adjustment and this can allow an appropriate large treatment to be done within the approved range.
3	Calculate an expected postsurgical keratometry value by adding the spherical equivalent of the proposed treatment in diopters to the average keratometry. The expected postoperative keratometry (allowing some room for retreatment) should ideally be >35.00 D and <50.00 D. Remember that for myopia the conversion factor for calculating the expected postoperative keratometry is 0.7 or 0.8 multiplied by the spherical equivalent added to the average keratometry.

CASE 28

A 56-year-old man with a history of hyperopia presents for LASIK consultation. He states that he could not tolerate contact lens wear. He has a history of bipolar disorder and anemia. His current medications include Effexor, Buspar, Wellbutrin, and Xanax. He has fainted several times in the past when he has had a blood test.

OD + 3.00 20/25+

OS + 2.75 + 0.50 × 90° 20/15

Add + 2.75 OU

Uncorrected Va

20/100 18 pt @ 14′

OD + 3.25 20/20-

OS + 3.50 20/15

OD + 3.00 20/20

OS + 3.50 20/15

OD 43.75 × 180°/43.75 × 90°

OS 44.00 × 180°/44.25 × 90°

Pachymetry

OD 551 µm

OS 551 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 4.0 mm

OS 4.0 mm

Additional Examination

Exposure is excellent, the refraction is stable, and the rest of the examination is normal.

Discussion

The clinician must assess this patient’s candidacy for LASIK from both the anatomical and the psychosocial perspectives. Is the patient’s psychiatric illness stable and might he be expected to have difficulty adapting to the changes that will occur following surgery? LASIK for hyperopia is quite different than for myopia. Regression is expected and, therefore, a significant age-dependent overcorrection must be built into the treatment. It can take as long as 6 months for the refractive error to stabilize. Initial myopia requiring distance glasses with transition over time to a need for reading glasses must be carefully explained and understood. The history of anemia should be investigated and addressed if necessary. Significant anemia may increase the risk for retinal and optic nerve ischemia while IOP is elevated. The history of vasovagal reaction should also not be overlooked. Whereas surgery with a patient in the supine position is beneficial, pretreatment with an intramuscular injection of 1 mL of atropine 0.4 mg/mL given 30 minutes prior to surgery can help block a vasovagal reaction. The hyperopic profile with the VISX laser requires a 9.0-mm ablation zone, so a large flap is necessary. The maximum ablation depth of 8 µm/D of correction occurs at a 5-mm diameter ring around the center of the ablation. Therefore, the cornea would have to be quite thin before the ablation depth made surgery unsafe.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring size	9.5 mm	9.5 mm	Large flap required for hyperopic LASIK
Plate size	160 or 180 µm	160 or 180 µm	Hansatome
Ablation zone	Hyperopic LASIK profile	Hyperopic LASIK profile	VISX STAR S4
Cycloplegic refraction used for treatment	+3.00 D	+3.50 D	Make sure full cycloplegia
Calculations using the hyperopic nomogram correction (see Table 7.2, page 77) (enter into VISX)	+3.00 × 30% = 0.90 +3.00 + 0.9 = +3.90 +3.90 D	+3.50 + 30% = 1.05 +3.50 + 1.05= +4.55 +4.55 D	Increase the correction to compensate for the expected postoperative regression; +4.55 D is close to the maximum +5.00 D approved for VISX
Ablation depth	3.9 D × 8 µm/D = 31 µm	4.55 D × 8 µm/D = 36 µm	Deepest ablation, 8 µm/D, occurs in a 5-mm diameter ring around the center of the ablation zone
RSB	551 µm – 160 µm – 31 µm = 360 µm	551 µm – 160 µm -36 µm = 354 µm	Hyperopic ablation is not deepest centrally, so RSB is significantly greater

Take-Home Points

1	Remember both the psychosocial as well as the anatomical criteria for LASIK surgery.
2	Pretreatment with 1 mL of atropine 0.4 mg/mL by intramuscular injection can help prevent a vasovagal reaction. May also be necessary for retreatment.
3	Significant anemia is a risk factor for ischemic injury related to increased IOP from the suction ring.
4	Overcorrection is necessary to compensate for the postoperative regression that often occurs with hyperopic LASIK.
5	Hyperopic patients need to be educated about the possible need for distance glasses after surgery and that it may take up to 6 months for the refraction to stabilize.

CASE 29

This 34-year-old woman presented for LASIK consultation. She had heard about customized treatment for correction of hyperopia and wondered if she was a candidate. She has become increasingly contact lens intolerant over the years and would like to decrease her dependence on glasses and contact lenses. She is in good health and has had no eye problems in the past. She takes birth control pills, but no other medication. Her grandmother had an attack of glaucoma in her 70s that was successfully treated with laser.

OD + 3.50 sph 20/25-

OS + 3.75 sph 20/25-

Uncorrected Va

20/100

20/200

OD + 4.00 + 0.55 × 60° 20/20-1

OS + 4.00 + 0.75 × 127° 20/20

OD + 4.17 + 0.65 × 55°

OS + 3.74 + 0.73 × 141°

OD + 4.25 + 0.50 × 60° 20/20

OS + 4.00 + 0.62 × 130° 20/20

OD 40.62 × 147°/41.12 × 57°

OS 40.12 × 45°/40.87 × 135°

Pachymetry

OD 562 µm

OS 570 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 7.5 mm

OS 7.2 mm

Additional Examination

The external, slit-lamp, and fundus examinations are normal. The angle is wide open and the IOP is 15 mmHg OU. WaveScan measurement showed 7.8% HOA and RMS 6.99 OD, and 6.4% HOA and RMS 7.73 OS.

Discussion

While pachymetry is a major concern in treating high myopia, it is somewhat less of a concern in high hyperopia, because the maximum ablation depth is less per diopter and the deepest ablation does not occur at the thinnest part of the cornea. For the high hyperopia treatment, corneal curvature becomes a more important concern. The resulting corneal curvature should ideally not exceed 50.00 D on keratometry. Adding the spherical equivalent of the correction to the preoperative average keratometry value provides an estimate of this value.

In this case, the cornea is flat so there is plenty of room to steepen the cornea without exceeding the limit just discussed. However, creating a flap with the microkeratome can be an issue in a patient with a flat cornea. There is increased risk of a free cap being created or a flap that is too small to accommodate the larger hyperopic ablation zone. A larger-diameter ring on the
microkeratome should be used. The femtosecond laser is an excellent alternative because the flap diameter created is independent of corneal curvature.

Often patients who have a higher level of hyperopia can have a latent component. The key here, as in myopic patients, is clinical correlation with the manifest, the cycloplegic, and the WaveScan refractions. Patients who have significant deviation should not be treated with the CustomVue platform.

Surgical Plan

The manifest, cycloplegic, and WaveScan refractions were well-matched, so no physician adjustment was used. Surgery was planned using the Hansatome (160-µm head and 9.5-mm ring) and CustomVue with the VISX STAR 4 laser. The surgery proceeded in an uncomplicated fashion.

Follow-Up Evaluation

At 3 months postoperatively, the patient presented with some overcorrection (myopic shift) OD > OS resulting in compromised uncorrected acuity, although best-corrected acuity remained unchanged from preoperative measurements.

Manifest Refraction	Uncorrected Va
OD -1.25 + 0.25 × 90° 20/20	20/50
OS -0.75 + 0.50 × 75° 20/20	20/30

In general, CustomVue hyperopic treatments tend to result in refractive errors near plano in the early postoperative period. The amount of overcorrection that resulted in this case occasionally occurs in high hyperopic corrections. This may be the result of the longer treatment time. Over time, the overcorrection tends to regress. If this persists at the 6-month postoperative visit and is stable, then a CustomVue enhancement can be considered in the same manner as a myopic enhancement case. In general, hyperopic CustomVue treatments tend to be closer to emmetropia earlier when compared with conventional treatments and therefore regress less.

Take-Home Points

1	Low hyperopia cases treated with CustomVue typically end up near plano postoperatively, but high hyperopic cases may be prone to overcorrection. This may be related to the longer treatment time.
2	Careful clinical correlation of manifest and wavefront refractions is extremely important in treating hyperopic patients.
3	Avoid cases when the estimated average postoperative keratometry is >50.00 D.
4	If the preoperative cornea is flat, use a large microkeratome ring or femtosecond laser.

CASE 30

A 49-year-old woman with a history of hyperopic astigmatism presents for consultation. She has worn toric soft contact lenses for many years and her refraction has been stable for more than 1 year. She had crossed eyes as a child and was treated with glasses only. Without glasses she currently is unable to see distance or near. She is right eye dominant.

OD + 2.50 + 1.25 × 94° 20/25-

OS + 3.75 + 1.50 × 86° 20/30

Uncorrected Va

CF distance; 18 pt near

OD + 3.00 + 1.25 × 90° 20/15

OS + 4.75 + 2.00 × 85° 20/20

OD + 3.00 + 1.50 × 90° 20/15

OS + 5.00 + 2.00 × 85° 20/20

OD 41.50 × 6/42.75 × 96°

OS 41.75 × 178/42.75 × 88°

Pachymetry

OD 505 µm

OS 501 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 7.0 mm

OS 7.0 mm

Additional Examination

The patient has a prominent brow, but lax lids and a wide palpebral fissure. The corneal diameter is 12 mm OU. The motility examination reveals an 8Δ esophoria at distance. The IOP and fundus examination are normal.

Discussion

Several useful teaching points are demonstrated in this case. In the evaluation, the pushed plus manifest refraction uncovered nearly all of the hyperopic correction noted in the cycloplegic refraction. The +3.75 D spherical equivalent and the +1.25 D of astigmatism in the right eye are well within the approved range for hyperopic LASIK even when 23% of the spherical equivalent is added to the sphere (per the nomogram for hyperopic LASIK on the VISX laser, Table 7.2, page 77).

This is not the case for the left eye. The nomogram percentage adjustment is 28% for a +6.00 D spherical equivalent in a 49-year-old, which would add 1.68 D to the spherical portion of the refraction. This would exceed the approved range for hyperopic correction with the VISX laser, which would require off-label use of the laser. Most surgeons would not advise off-label use of the laser and would instead look for alternatives. Some surgeons prefer to avoid keratorefractive surgery near the approved upper limits for myopia and hyperopia. The patient should be informed that at the upper extremes of approved treatment, a loss of best-corrected acuity or reduced night vision might occur. Clear lens extraction with a toric IOL or LRI would be an alternative for the hyperopic patient, whereas a phakic IOL might be a better choice for the high myope due to the risk of retinal detachment. In this case, a surface ablation procedure would be an alternative to LASIK for the left eye. PRK does not require a nomogram adjustment. The surgeon can use the cycloplegic refraction if it is close to the manifest refraction.

A large flap is required for hyperopic LASIK in order to accommodate the 9.0-mm treatment zone. In this case, the keratometry values are >45.00 D, so an 8.5-mm Hansatome ring would be an acceptable choice. Because of the prominent brow, the surgeon should be prepared to position the patient in the chin-up position to achieve better exposure. The corneas are somewhat thin, but this should not pose a problem for this hyperopic patient. Keep in mind that a thin flap is likely to occur with a microkeratome and with the same blade the flap in the second eye would be even thinner. The femtosecond laser is less dependent on corneal thickness in creating flaps of a desired thickness.

As with any hyperopic patient, it is important to discuss the slower visual rehabilitation and the possible need for distance glasses. If the PRK option is selected for the left eye, the rehabilitation will be even slower. The epithelial debridement will need to be large enough to accommodate the 9.0-mm ablation zone and will therefore take the surface longer to heal and stabilize. The final point is to explain in lay language to this esophoric patient that in the event of postoperative anisometropia, added strain on fusion might result in symptomatic diplopia.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring size for LASIK	8.5 mm	9.0-mm epithelial debridement	Steep small cornea; 8.5-mm ring is the better choice OD
Plate size for LASIK	160 µm or 180 µm	Not applicable	Thin flaps result from mechanical microkeratome flaps in thin corneas
Ablation zone	9.0 mm	9.0 mm	VISX STAR S4
Spherical equivalent	+3.75 D	+6.00 D
Calculations with nomogram correction	+3.75 × 23% = 0.86 +3.00 + 0.86 = +3.86	+6.00 × 28% = +1.68 +5.00 + 1.68= +6.68 (see comment)	+6.68 (sphere + nomogram adjustment) exceeds the FD-Aapproved limit. With PRK, treat on cycloplegic refraction
(enter into VISX)	+3.86 + 1.50 × 90°	+5.00 + 2.00 × 85°
Ablation depth	4.61 D × 8 µm/D = 37 µm	6.00 D × 8 µm/D = 48 µm
RSB	505 µm – 160 µm – 37 µm = 308 µm >250 µm	501 µm – 160 µm – 48 µm = 293 µm >250 µm	Hyperopic ablation is not deepest centrally, so RSB is greater

Take-Home Points

1	If the spherical equivalent plus the nomogram adjustment exceeds the approved limit for the laser, consider using PRK, which does not require a nomogram adjustment.
2	Explain to patients that at the extremes of approved hyperopic treatment, a loss of best-corrected postoperative visual acuity can occur.
3	Clear lens extraction with a toric IOL to correct astigmatism, a multifocal IOL (provided both eyes will ultimately be treated), or an accommodating IOL with LRI are additional options when the amount of hyperopic correction is excessive.

CASE 31

A 66-year-old woman had eight-cut RK in the left eye 10 years ago. She continued to wear a soft contact lens in the right eye. Over the years, she developed decreasing vision in the left eye and symptoms of eyestrain. She wondered if laser surgery could improve her symptoms. She was not interested in monovision and was made aware she would need reading glasses following surgery. She understood the risks of surgery. After being out of her contact lens, her refraction was followed until stable. Old records were obtained and the refraction in the OS was stable over the previous 18 months.

OD – 4.50 20/20-3

OS + 3.00 + 1.25 × 30° 20/20+

Uncorrected Va

OD CF

OS 20/400

OD – 4.75 20/15

OS + 3.00 + 0.75 × 40° 20/20+

OD – 4.50 + 0.50 × 175° 20/15-

OS + 3.00 + 0.75 × 40° 20/20±

OD 44.75 × 15°/ 45.00 × 175°

OS 37.12 × 12°/38.50 × 102°

Pachymetry

OD 510 µm OS 498 µm (≥537 µm in midperiphery)

Topography

Regular OD Central flattening OS

Scotopic Pupils

OD 5 mm

OS 5 mm

Additional Examination

The keratometry reading OS prior to RK was 44.00 D × 44.25 D @ 180°. The RK incisions are thin without noticeable epithelial plugs. There is no corneal neovascularization. The cornea is otherwise clear. There is no cataract. The IOP and fundus are normal.

Discussion

LASIK surgery can be safely performed following RK, provided the conditions are optimal. The RK scars should be thin and free of large epithelial plugs. Ideally, there should be at most only minimal irregular astigmatism; that is, the patient should be correctable to 20/20. If the BCVA is <20/20, the postoperative LASIK result is less predictable.

The cornea is somewhat thin centrally. This was presumably present preoperatively, because RK would not thin the uninvolved central cornea. The thin cornea does not preclude hyperopic LASIK, because the deepest ablation is at 5 mm and is only 8 µm/D. Although the central cornea is flat, the microkeratome will engage the cornea in the periphery where the cornea is not so flat. The risk of a free flap is small. Base the ring diameter on the preoperative keratometry. When the flap made with the microkeratome is lifted, care is required to avoid disrupting the incisions. A thicker flap is usually an advantage to avoid separation. If the incisions do separate, the excimer procedure can still be done, but the pieces should be meticulously replaced at the end of the procedure and a bandage soft contact lens (BSCL) placed. The risk of epithelial ingrowth is probably increased if this occurs. Femtosecond laser should not be used following RK because the required flap dissection could potentially disrupt the RK incisions. In addition, the waste gases from photodisruption can push anteriorly through the RK incisions, so-called vertical gas breakthrough, and form a small buttonhole.

The hyperopic nomogram adjustment is different following RK (see Table 7.2, page 77) and in a 66-year-old woman, a 2% addition is suggested. For patients under age 50, in contrast to standard hyperopia, a reduction in the hyperopic correction is suggested. The hyperopic nomogram is also different for treatment of consecutive hyperopia following LASIK.

Because the right cornea is somewhat thin, the femtosecond laser might be a better choice than the microkeratome. The laser is capable of greater precision with regard to flap thickness. The microkeratome usually will create a thinner flap in a thinner cornea.

Given the patient’s age, a discussion of monovision is warranted. If desired, determine the nondominant eye and either reduce the myopic correction or increase the hyperopic correction appropriately.

Surgical Plan
	Right Eye	Left Eye	Comments
Ring size	IntraLase 9.0-mm flap diameter in case retreatment needed	9.5 mm	Preoperative K < 45.00 D
Plate size	IntraLase 110-µm flap depth, usually creates a flap not greater than 120 µm	180 µm	Hansatome flap in a thin cornea can be quite thin. Very thin flap after RK is a disadvantage
Ablation zone	6.0 mm	9.0 mm	Hyperopic protocol OS
Calculations with nomogram correction (enter into VISX)	-4.25 D × 9% = 0.38 -4.50 + 0.38 = -4.12 -4.12 + 0.50 × 175	+3.00 + 0.75 × 40° See Table 7.2 for nomogram adjustment +3.375 × 2% = 0.07 +3.07 + 0.75 × 40°	+2% nomogram adjustment for a 66-year-old with consecutive hyperopia after RK
Ablation depth	4.25 D × 12 µm/D = 51 µm	3.445 D × 8 µm/D = 28 µm	Spherical equivalent × appropriate conversion
RSB	510 µm – 120 µm – 51 µm = 339 µm >250 µm	498 µm – 180 µm -28 µm = 290 µm >250 µm	RSB OS likely >291 µm because flap likely to be thinner than 180 µm and hyperopic treatment is not deepest centrally

Take-Home Points

1	LASIK can safely be done following RK if there is no more than minimal irregular astigmatism, thin well-healed scars, and no large epithelial plugs.
2	The microkeratome should be used rather than the femtosecond laser, with the ring size based on the preoperative keratometry.
3	Should the flap separate, carefully replace the pieces after the excimer ablation has been completed and place a bandage contact lens on the eye.
4	The suggested nomogram adjustment for consecutive hyperopia following RK is considerably different than for treatment of primary hyperopia (see Table 7.2). A reduction rather than an addition to treatment may be required for patients under 50.

CASE 32

A 58-year-old woman was referred for management of painful recurrent corneal erosions, which had occurred in both eyes over a 2-year period. The pain would always begin in the early morning and last from a few hours to a few days. The episodes occurred at least once a week and she could never predict when an erosion would occur. Her mother had similar problems for years before she died of heart disease. She had tried tear supplements, hypertonic sodium chloride ointment, and drops, as well as a BSCL without relief of her symptoms. Epithelial debridement was tried in the left eye, but the symptoms recurred. Fortunately, her vision in spectacles remains excellent at distance and near. She is amenable to any suggestion that would allow her life to return to normal. She has heard about LASIK surgery from a friend and wonders if it would help her.

OD + 2.25 20/25

OS + 2.00 20/25

Uncorrected Va

20/200

OD + 2.25 + 1.00 × 25° 20/20-

OS + 2.00 + 1.00 × 160° 20/20-

OD + 2.25 + 1.00 × 30° 20/20-

OS + 2.25 + 1.00 × 164° 20/20-

OD 41.00 × 112°/41.75 × 22°

OS 40.87 × 70°/41.50 × 160°

Pachymetry

OD 534 µm

OS 536 µm

Topography

Regular astigmatism OU

Scotopic Pupils

OD 5.0 mm

OS 5.0 mm

Additional Examination

The slit-lamp examination was significant for dots and fingerprints on the surface of the paracentral and mid-peripheral cornea OU. There was no evidence of corneal scarring or corneal neovascularization; and no staining with fluorescein. The anterior segment was otherwise completely normal. The IOP and fundus examinations were normal.

Discussion

This patient suffers from epithelial basement membrane dystrophy, which she likely inherited from her mother. Conventional treatments with lubricants, hypertonic NaCl, BSCL, and debridement have failed to control the patient’s symptoms. Anterior stromal puncture is a treatment that has not been tried. In the absence of a frank erosion, it might be difficult to know exactly where to apply the punctures. The patients with this dystrophy often have diffuse involvement. This patient is a poor candidate for LASIK surgery because of the high risk of epithelial sloughing. The corneal hypoesthesia associated with LASIK might afford some pain relief, but cutting the corneal nerves to relieve corneal erosions symptoms is not a practical solution.

PRK is a practical solution, which would ultimately relieve symptoms, stabilize the cornea, and correct the hyperopic astigmatism with one procedure. Phototherapeutic keratectomy (PTK) has been described as a remedy for recurrent corneal erosion. The hyperopic ablation would treat all but an 0.8-mm central area within a 9.0-mm ablation zone. No nomogram adjustment is needed with hyperopic PRK. Her cornea has ample thickness and would not become abnormally steep after the treatment. Provided the patient understands the risk of surgery, PRK is an excellent therapeutic option for this patient.

Surgical Plan
	Right Eye	Left Eye	Comments
PRK OU
Ablation zone	9.0 mm	9.0 mm	VISX STAR S4
Enter into VISX	+2.25 + 1.00 × 25°	+2.25 + 1.00 × 160°	No nomogram adjustment needed for hyperopic treatment
Ablation depth	+2.75 D × 8 µm/D = 22 µm	+2.75 D × 8 µm/D = 22 µm	Low risk of central haze

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Tags: LASIK Handbook The: A Case-Based Approach

Jul 20, 2016 | Posted by drzezo in OPHTHALMOLOGY | Comments Off

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