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

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Tags: LASIK Handbook The: A Case-Based Approach

Jun 5, 2016 | Posted by drzezo in OPHTHALMOLOGY | Comments Off

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