Basic LASIK
Robert S. Feder
▪ Patient Evaluation
Careful patient evaluation is essential in order to determine whether a patient is a candidate for LASIK surgery. The criteria used to determine candidacy are divided into two parts, psychosocial and anatomical. Each will be considered individually.
PSYCHOSOCIAL FACTORS
A good candidate for LASIK surgery should be capable of understanding the risks of the procedure and that risk-free surgery does not exist. The patient must be willing and able to follow instructions before, during, and after surgery. A patient who resists listening to a discussion of the risks may be a poor candidate for surgery. If the patient is unable to understand the surgeon due to a language barrier or disability, adequate preoperative counseling and intraoperative instructions will be more difficult to achieve. The patient must be available for postoperative follow-up. Beware of the patient with a challenging schedule who may not understand the care that is required after surgery.
Managing patient expectations is one of the greatest challenges a LASIK surgeon faces. This begins during the preoperative consultation. The patients should be told what level of visual acuity is reasonable to expect, with a subsequent enhancement procedure if needed. This can be expressed as an expected range of visual acuity a particular patient would be likely to achieve. It is helpful to mention the surgeon’s rate of enhancement for patients of a similar age with similar refractive error. A patient who expects perfection after surgery is destined to be unhappy postoperatively. Do not confuse visual acuity with visual function. A patient with 20/20 Snellen acuity may be unhappy due to loss of near vision, ghosting, decreased contrast sensitivity, glare, or other problems that affect the quality of vision. Personal characteristics of the best LASIK patients include an easygoing nature, a positive outlook, a welladjusted personality, a patient comfortable using less than a full refractive error correction, and a willingness to wear glasses for reading or night driving. Intense individuals, patients with a grim outlook, highly emotional or vitriolic patients, or highly critical patients may not be well suited for LASIK surgery.
The patient’s psychosocial candidacy for the procedure should be assessed while the history is taken as well as during the examination. Input from well-trained technicians or office personnel is valuable information that should not be dismissed. However, it should not be considered a substitute for the surgeon’s personal evaluation.
ANATOMICAL FACTORS
In general, the most reproducible results are obtained when LASIK is performed on a healthy patient with healthy eyes. There is less risk when the orbital and lid anatomy allow adequate exposure for the microkeratome or a femtosecond laser ring. The refractive error should preferably be well within the approved limits for the specific excimer laser being used (see Table 1.1). Patients with severe dry eye, absent corneal sensation, or inadequate eyelid closure are poor candidates for surgery. If a mechanical microkeratome is to be used and the corneal contour is abnormally steep or flat, the surgeon and the patient should be aware of the increased respective risks of buttonhole and free cap. The risk of buttonhole or free cap related to abnormal contour is of less concern when the flap is created with a femtosecond laser. LASIK may be a poor choice if the corneal diameter is unusually small. Finally, the corneal thickness is a major factor in determining the amount of refractive error that can safely be treated.
EVALUATION
A standardized laser refractive surgery form, designed for recording the history and examination, can assist the surgeon in documenting pertinent information in an orderly manner. Using such a form can reduce the chance of inadvertent oversight in the evaluation. A sample preoperative form is shown in Figure 1.1. Postoperative forms are also helpful (Fig. 1.2). There is an advantage to using a form in which the results of multiple postoperative visits can be easily tracked. The sample forms shown in Figures 1.1 and 1.2 can be modified to suit the particular needs of a surgeon or practice. As practices transition to electronic medical records, templates should be modified to incorporate elements required for LASIK evaluation. While risks can be quickly recorded in a dot phrase, it is worthwhile to addend the statement to document the discussion of particular risks that are relevant to the specific patient.
History
The history should begin with a question about the patient’s goals for surgery. While LASIK surgery is approved for patients at least 18 to 21 years of age, many patients will not have attained refractive stability by this age. The refractive history should contain questions about refractive stability. Ideally the refraction should be stable for at least 1 year before LASIK surgery is considered. If a glasses change of >0.50 diopter (D) has occurred within 1 year, the patient should be reevaluated at 6-month intervals until the measurement is stable. Patients approaching age 40 years should be questioned about their willingness to wear reading glasses. A contact lens history should be obtained and should include the type of lens (e.g., hard, rigid gas permeable, or soft), the duration of lens wear in years, and the typical duration of daily lens wear or use of extended wear. The use of contact lenses to obtain monovision should be noted. The contact lens prescription should be obtained. This will help the surgeon plan the proper amount of undercorrection in the nondominant eye of a myopic patient. If the presbyopic myope has not previously used a monovision correction and is interested, a contact lens trial, undercorrecting the nondominant eye, will need to be tried at home, at work, and during leisure activities. If the patient has an astigmatic component in the refraction, a spherical contact lens correction may not adequately simulate a myopic astigmatic laser treatment. If the contact lens trial is successful, surgical monovision may be an option.
The past ocular history should be obtained. A history of recurrent corneal erosion, corneal ulceration or other ocular infection, glaucoma or glaucoma surgery, or cataract may all have an impact on the patient’s candidacy for LASIK surgery. Past medical history including diabetes, rheumatoid arthritis, systemic immunosuppression, pregnancy, or nursing an infant is important. Diabetics, in addition to retinal ischemia and edema, may have poor epithelial adhesion, increasing the risk of erosion. They may also be more likely to have cataract. Approval may not have been obtained for laser refractive surgery in patients with certain systemic diseases such as rheumatoid arthritis. If off-label use of the laser is entertained, the patient should be made aware that this is the case. Pregnant or nursing patients may have unstable refractions, and it is best to delay surgery until 6 to 12 weeks after nursing has ended. Patients who become pregnant after LASIK should understand that a refractive error change may result from the pregnancy and may not be caused by regression of the effect of refractive surgery. The change may resolve after delivery without retreatment.
TABLE 1.1 FDA-Approved Indications for Excimer Laser Refractive Surgery | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 FIGURE 1.1 Sample preoperative refractive surgery consultation form. |
 FIGURE 1.2 Sample postoperative refractive surgery form. |
Examination
Visual acuity at distance and near should be measured with and without correction. The best-corrected visual acuity should be at least 20/20 preoperatively. If the acuity is <20/20, the surgeon must seek an explanation. If the acuity is reduced because of refractive amblyopia, the patient may still be a candidate for surgery, provided the patient has realistic expectations for postoperative vision. Reduced preoperative visual acuity related to irregular corneal astigmatism is a contraindication to LASIK surgery.
Contact lens wear will need to be discontinued until the refraction becomes stable. In general, refractive stability will take longer for rigid gas permeable lens users than for soft lens users. The duration of lens wear and the intensity of lens wear are also important factors affecting the time to achieve refractive stability. A rule of thumb for patients wearing soft lenses or hard lenses for 10 years would be to discontinue lens wear for 2 and 4 weeks, respectively. Longer duration of lens wear will likely require longer periods of abstinence. Serial examinations are recommended to ensure refractive stability. Once stability is achieved and final measurements are acquired, the patient can return to lens wear until a few days prior to surgery.
For myopia, the manifest refraction should not differ from the cycloplegic refraction by >0.50 D, and the axis of cylinder should not differ by more than 15 degrees. For hyperopia, the manifest and cycloplegic refractions should not differ by >0.75 D.
Keratometry values should be used to calculate the predicted postsurgical corneal contour. If the estimate of the postsurgical corneal contour is <35.00 D, keratorefractive surgery outcome may be less than ideal because the cornea may be too flat to support good visual function. To estimate the postsurgical corneal contour, the spherical equivalent of the proposed treatment is multiplied by a conversion factor of 0.7 or a more conservative 0.8. The product is subtracted from the average of the keratometric values. If the result is only slightly >35.00 D, a significant retreatment may leave the cornea too flat to support good visual function. This possibility would be important to discuss with a patient who has such a preoperative estimate. Hyperopic treatments induce corneal steepening. The conversion factor for estimating postoperative steepening is 1.0 and the postoperative cornea should remain below 50 D.
Ocular dominance should be recorded. It can be determined by asking the patient to wink. Generally, patients have difficulty winking the dominant eye. Hand the patient a disposable camera and ask the patient to pretend to take a picture. The camera will be held in front of the dominant eye. Finally the patient can be asked to create an “o” with the fingers and thumb on each hand and then create a tube by stacking the hands. The patient will use the dominant eye when asked to look through the tube. Ocular dominance is important in performing a monovision treatment. The dominant eye is usually corrected for distance.
A careful external examination is required to identify diseases such as acne rosacea, which can be associated with ocular inflammation, and may require treatment prior to surgery. In addition, an assessment of the degree of ocular exposure is essential. The surgeon should determine whether the degree of lid laxity, the orbital aperture, the prominence of the brow, the position of the globe,
and palpebral fissure height are adequate to accommodate a flap making apparatus. If the aperture is small or tight or if the eye is deep set, photorefractive keratectomy (PRK) may be a more preferable option.
and palpebral fissure height are adequate to accommodate a flap making apparatus. If the aperture is small or tight or if the eye is deep set, photorefractive keratectomy (PRK) may be a more preferable option.
Significant lagophthalmos and associated exposure may be problematic postoperatively, given the temporary neurotrophic status of the flap. If the eyes are dry, the patient can be reassessed 1 month after initiating treatment with tear supplements, topical cyclosporine, and/or punctal plugs. Encouraging good oral hydration is also important in patients who exercise heavily. If significant tear deficiency remains despite these measures, LASIK should be avoided. Low ambient humidity in the patient’s work or home environment will be unfavorable for the borderline dry eye patient. Patients who do extensive reading or computer work may be at greater risk of an evaporative dry eye postoperatively.
The patient should be examined for the presence of a relative afferent pupillary defect. The pupil diameter can be measured in the dark with one of the commercially available devices designed for this purpose, for example, a Colvard pupillometer (OASIS Medical, Inc., Glendora, CA). The significance of large pupil size and its relationship to the quality of night vision is not at all certain. There is convincing evidence that pupil size is not a significant factor in predicting postoperative glare and haloes (refer to Suggested Readings). Many surgeons believe that reducing higher order aberrations with custom treatment is much more important. The degree of myopic correction is a much more significant factor. Some surgeons routinely use the largest treatment zone possible given corneal thickness constraints regardless of pupil size. Others continue to prefer a treatment zone that extends beyond the edge of the dark-adapted pupil in the hope of minimizing night vision symptoms, despite the lack of strong supportive evidence.
Motility function should be assessed to rule out a latent condition that might become symptomatic in the event of significant postoperative anisometropia. This is especially true in the case of a patient considering monovision treatment or for the patient with a past history of strabismus surgery. A patient able to control a significant phoria may develop diplopia, if fusion is disrupted. A patient with a moderateto large-angle alternating tropia may tolerate monovision, because this individual currently fails to use the eyes together and is capable of using either eye independently. Monovision may not be suitable for a patient with a constant tropia and a strong fixation preference for one of the eyes. Monovision would force this patient to use the deviated, nondominant eye for near vision, which might seem unnatural.
The slit-lamp examination should begin with an assessment of the lids and lashes. Inflammation in this area should be controlled prior to surgery. It is critically important to rule out the presence of corneal pathology. Contact lens—wearing patients may have peripheral corneal neovascularization, punctate keratopathy, sterile keratitis, stromal thinning, scarring, or subepithelial fibrosis. Keratitis and punctate keratopathy are usually reversible and may clear after a period of time without lens wear. Active keratitis is a contraindication to LASIK surgery. If it does not clear spontaneously, a treatment regimen should be initiated and the patient reevaluated. Subepithelial fibrosis and neovascularization are permanent changes that may impact the surgical plan or the decision to do surgery.
Corneal diameter should be noted. If the cornea is small it may be challenging to reliably create a microkeratome flap of adequate size to accommodate the proposed ablation. A surface ablation procedure may be the better option, however, the femtosecond laser may allow the surgeon greater control over flap diameter making safe LASIK possible.
Special attention to the corneal thickness is important. If the cornea is thin, the residual stromal bed following the intended treatment might be inadequate to support a stable corneal contour long term, increasing the risk of post LASIK ectasia. In such a case LASIK surgery may be contraindicated. The preoperative corneal contour should be regular. An irregular contour suspected on slit-lamp examination should be investigated with corneal topography. LASIK surgery is most reliable when the contour is regular.
Corneal scarring within the proposed ablation zone is a relative contraindication to the surgery. LASIK may be possible if scarring is in the periphery and thinning is mild, provided
the cause is not prior herpes simplex keratitis. Herpes viral infections can be reactivated by the ultraviolet radiation of the excimer laser. The presence of epithelial basement membrane dystrophy may indicate a possible defect in epithelial adhesion. Patients with this dystrophy are more likely to experience epithelial sloughing, possibly with diffuse lamellar keratitis or epithelial ingrowth. The risk of epithelial sloughing has been substantially reduced with the femtosecond laser. Patients with confluent guttae may be at risk for poor flap adhesion postoperatively, if the endothelial pump functions poorly. An abnormally thick cornea, especially in the early morning, may be a sign of abnormal endothelial pump function.
the cause is not prior herpes simplex keratitis. Herpes viral infections can be reactivated by the ultraviolet radiation of the excimer laser. The presence of epithelial basement membrane dystrophy may indicate a possible defect in epithelial adhesion. Patients with this dystrophy are more likely to experience epithelial sloughing, possibly with diffuse lamellar keratitis or epithelial ingrowth. The risk of epithelial sloughing has been substantially reduced with the femtosecond laser. Patients with confluent guttae may be at risk for poor flap adhesion postoperatively, if the endothelial pump functions poorly. An abnormally thick cornea, especially in the early morning, may be a sign of abnormal endothelial pump function.
All abnormalities of the anterior segment should be noted. The presence of cataract may be a contraindication to LASIK surgery. It is best to avoid LASIK surgery on the patient with a visually significant or progressive cataract. Lens-induced myopia from a nuclear cataract can be misinterpreted as LASIK regression. Glare from a posterior subcapsular cataract might be thought to be due to the refractive surgery.
If a peripheral cataract is found on the presurgical examination, it is wise to follow the patient until it can be determined whether or not the cataract is progressive. The patient who decides to proceed with refractive surgery should be informed that, although the cataract may appear to be stable and not visually significant, it could unexpectedly progress and undermine the LASIK result. If cataract surgery is needed, determination of the lens implant power will be more challenging than it otherwise would be. If standard keratometry is used in biometry for a cataract patient after LASIK surgery has been done, the selected lens implant may be underpowered. This topic is more completely discussed in Chapter 14.
Intraocular pressure (IOP) should be measured preoperatively. If the cycloplegic refraction is to be done on the same day, the pressure should be measured following the refraction in order to avoid disturbing the corneal surface. If IOP is elevated, the significance should be interpreted. The pressure would, for example, be less significant if the cornea is thicker than normal and the optic nerve is normal. Significant optic nerve cupping should be evaluated with visual field evaluation and possibly an ocular coherent tomography (OCT) to assess nerve fiber layer thickness. In the presence of glaucomatous field changes, the potential for nerve damage occurring when the suction ring increases the eye pressure should be considered. In this situation, an alternative refractive surgery option such as a surface ablation procedure can be discussed with the patient. If the patient has a filtering bleb, a suction ring should not be used. Finally, one must recognize that IOP measurement in a thin postoperative patient may be less accurate.
The dilated fundus examination is an essential part of the preoperative evaluation. While it need not be done during an initial screening examination, it must be done prior to surgery. If significant abnormalities are found, the patient should be informed. The cycloplegic refraction on which the LASIK treatment is based should be performed before the retina is exposed to intense illumination.
The fundus examination is particularly important for the myopic patient who is at greater risk for retinal detachment. In the presence of peripheral retinal pathology, a consultation from a retinal specialist is advisable. The result of this consultation should be included in the record. Preoperative prophylactic treatment can be delivered if required. The retina surgeon should determine the timing of LASIK surgery, following any treatment. If a retinal problem were to develop postoperatively, the patient will already have a relationship with a specialist.
Diabetic retinopathy if present may impact the decision to do LASIK. Patients with evidence of significant retinal ischemia may be at risk for an ischemic event related to intraoperative IOP elevation. Macular edema, epiretinal membranes, and degenerative changes in the macula may all limit the postsurgical visual outcome. These issues should be discussed with the patient. It is not uncommon for previously undiagnosed retinal disease to be uncovered during the LASIK evaluation.
If the optic nerve does not appear normal, an evaluation of optic nerve function should be conducted. This evaluation would include measurement of central acuity, pupil reactivity,
color vision, brightness comparison, and visual field. Obviously, some of this evaluation will already have been done before the retinal examination. Highly myopic patients often have tilted discs with peripapillary atrophy. The surgeon should rely on his or her own experience to determine if the appearance of the disc is inconsistent with the patient’s refractive error.
color vision, brightness comparison, and visual field. Obviously, some of this evaluation will already have been done before the retinal examination. Highly myopic patients often have tilted discs with peripapillary atrophy. The surgeon should rely on his or her own experience to determine if the appearance of the disc is inconsistent with the patient’s refractive error.
Corneal pachymetry should be measured after the refraction has taken place to prevent surface disruption. This is a critical measurement and should be performed with an ultrasonic device. The surgeon is cautioned against relying on slit-beam-generated pachymetric maps; for example, Orbscan (Bausch & Lomb, Rochester, NY), to determine whether the cornea is thick enough for LASIK surgery. These maps provide a relative comparison of thickness at different points on the cornea but may not accurately measure the corneal thickness at any one point. Sheimpflug-based pachymetric maps as generated by Pentacam (Oculus, Inc., Lynnwood, WA) provide accurate measurements of corneal thickness. It reliably determines the thinnest part of the cornea and can be used in lieu of ultrasonic pachymetry. When ultrasonic pachymetry is relied upon, care must be taken to be certain that the thinnest part of the cornea is being measured. Remember the thinnest part of the cornea may not be in the center, for example, pellucid marginal degeneration (PMD) or forme fruste keratoconus (FFKC).
Because contact lens wear can increase corneal thickness, it is more accurate to measure the thickness after the patient has discontinued lens wear. However, if the patient is measured just after contact lenses have been removed and the cornea is too thin for LASIK surgery, a second measurement following a period without contact lens wear will usually not improve the patient’s candidacy for surgery. If the cornea is significantly thicker than 620 µm, one must determine whether abnormal endothelial function is the explanation. A correlation with the slit-lamp evaluation and possibly specular microscopy is indicated in this situation. While the cornea may be thicker than normal with normal endothelial function, the consequence of not detecting poor endothelial function is a postoperative flap adhesion problem.
Corneal topography must be done on every patient prior to LASIK surgery in order to avoid operating on a patient with an abnormal corneal contour. When the contour is abnormal preoperatively, the postoperative outcome is unpredictable, even when the cornea is of adequate thickness.
The topographical analysis may also indicate significant contact lens-induced irregularity. Serial topography performed during a period of contact lens abstinence can be used to track the corneal contour during the resolution of the irregularity and ultimately confirm that the corneal surface has become regular and stable.
The refractive surgeon must be capable of identifying preclinical or forme fruste keratoconus. A young patient with subtle signs of ectasia may go on to manifest the clinical signs of keratoconus over time. Refractive surgery would hasten the development of symptomatic disease. Pellucid marginal degeneration is a noninflammatory thinning disorder in which there is typically a band of inferior thinning with protrusion of the cornea superior to the thin area. Laser refractive surgery should also be avoided in patients with PMD. This condition has a characteristic power map sometimes described as a “crab claw” appearance. Corneal topography including the signs of early keratoconus is discussed in greater detail in Chapter 2.
No one method is foolproof for reducing the risk of postoperative ectasia. It is recommended that multiple factors and analyses be used to determine whether a particular patient is suitable for keratorefractive surgery. Randleman et al.1 have developed a conservative ectasia risk scale that combines corneal topography pattern, residual stromal bed thickness, patient age, preoperative corneal thickness, and manifest refraction spherical equivalent. Risk assessment for ectasia after corneal refractive surgery is discussed later on in this chapter in greater detail.
Wave scan can be done at the same time as topography if custom LASIK is being considered; however, wave scan is not a substitute for topography. The scan used for the actual surgery should be obtained after the patient has been out of contact lenses long enough for
the refraction to stabilize. The wave scan will determine the degree and type of higher order aberrations. It also determines the refractive error in an objective way that can aid the surgeon when performing refraction. wave scan technology can be used postoperatively to assess the degree of higher order aberrations that may be induced by refractive surgery. The nuances of wave scan interpretation and custom LASIK as performed with several commonly used systems will be discussed later in the text.
the refraction to stabilize. The wave scan will determine the degree and type of higher order aberrations. It also determines the refractive error in an objective way that can aid the surgeon when performing refraction. wave scan technology can be used postoperatively to assess the degree of higher order aberrations that may be induced by refractive surgery. The nuances of wave scan interpretation and custom LASIK as performed with several commonly used systems will be discussed later in the text.
DISCUSSING THE RISKS OF SURGERY
Presentation Overview
One of the greatest challenges for the beginning LASIK surgeon is to explain the actual operation and the risks of the procedure with confidence and in a manner that informs without terrifying the patient. The choice of words will make a significant difference in the patient’s perception of the procedure and the surgeon. Speaking in lay language, in a manner easily understood by the patient, is key to communicating the information needed to make an informed decision. A discussion presented with enthusiasm will help as well.
The explanation of the procedure and the risks should follow the examination. If the surgeon uncovers a contraindication to LASIK surgery, this can be explained and the consultation concluded without having gone through a detailed discussion.
Explain to the patient that the discussion will cover most of the commonly asked questions. Encourage the patient to interrupt if a particular point is not clear or if there is a question, and inform the patient that there will be time at the end to ask any additional questions. Remember the goals of the dialogue are both to inform completely and reduce anxiety. Anticipate your patient’s questions and answer them before the patient needs to ask them. For example, if you wear glasses, anticipate that your patient will want to know why you haven’t had the procedure. Have an answer prepared so you can present this information without being asked. This helps to instill confidence. Withholding information is improper and may increase anxiety and contribute to dissatisfaction with the surgery. Proper preoperative preparation will make the entire surgical process easier for the patient, surgeon, and staff. While many surgeons have others in the office explain the procedure and risks, there is an advantage for the surgeon to have the discussion personally. There is an opportunity to get to know this patient and determine his or her candidacy for the procedure from a psychosocial perspective. If the patient is unusually nervous, acts in an inappropriate way, seems inattentive or suspicious, or appears to have unreasonable expectations, he or she may be a poor candidate.
It is helpful to listen to one or more experienced surgeons present this material. A recording of the presentation or a typewritten script can help the beginning surgeon to prepare the first few discussions with prospective patients. Over time the surgeon will develop a talk that incorporates both the answers to questions that arise during discussion as well as portions of other doctors’ presentations that seem to fit appropriately. When the presentation feels natural, the physician will appear self-assured and the patient will sense this.
Because one of the goals of the initial encounter is to instill the patient with feelings of confidence and comfort with the surgeon and staff, try to minimize the wait time in the office prior to the consultation and at every postoperative visit. During introductions, ask the patient how he or she prefers to be called and ask permission to address the patient in that manner.
Sample Preoperative LASIK Patient Discussion
Here is a sample LASIK presentation. It should be tailored as needed for each individual patient. Dialogue directed to the patient is in italic type. What are you hoping LASIK surgery will do for you? The most common response is “to get rid of my glasses and contact lenses.” The ideal response is “to become less dependent on glasses and contact lenses.” Responses such as “I want to be more attractive,” “I want to improve my vision beyond what I see in glasses or contact lenses,” or “I don’t know, I just want the surgery” are not particularly
appropriate and should raise a red flag about the candidacy of the particular patient. At this point it is helpful to remind the patient that LASIK reduces the dependence on glasses and contact lenses, but that glasses may be needed for reading when one reaches the mid-40s. “Correcting the dominant eye for distance and the nondominant eye for near, can reduce the need for reading glasses. This is called monovision.” This discussion is appropriate for patients of presbyopic age. “Glasses may also be needed for some distance activities, such as driving at night or in the rain, but it is rare for patients to require distance glasses full time.”
appropriate and should raise a red flag about the candidacy of the particular patient. At this point it is helpful to remind the patient that LASIK reduces the dependence on glasses and contact lenses, but that glasses may be needed for reading when one reaches the mid-40s. “Correcting the dominant eye for distance and the nondominant eye for near, can reduce the need for reading glasses. This is called monovision.” This discussion is appropriate for patients of presbyopic age. “Glasses may also be needed for some distance activities, such as driving at night or in the rain, but it is rare for patients to require distance glasses full time.”
Vision Expectations. The first question every patient wants an answer to is, “How well will I see after surgery?” If the patient is a myope with ≤ -10.00 D of spherical error and ≤ +3.00 D of cylindrical, it is reasonable to expect an uncorrected visual acuity of 20/25 or better. “Retreatment may be required to achieve this level of visual acuity. A typical retreatment rate is approximately 10%, meaning 90% of patients achieve their vision goals with one laser surgery. Retreatment rates are generally higher for patients who need stronger glasses.” It is important to explain to the hyperopic patient that in order to successfully correct distance vision in the long run, an initial overcorrection is necessary. This will result in good near vision, but blurring in the distance, and may require the need for distance glasses. Over a 3- to 6-month period the distance vision will improve and the near vision may weaken.
Night Vision. “Nearsighted patients often feel they don’t see as well at night. They may be aware of glare from car headlights or haloes around streetlights.” If the patient does not appear to understand what glare is, dim the overhead lights and shine a light toward the patient from 2 to 3 feet away. Ask the patient if rays of light are seen coming from the light source. “It is important for patients to become familiar with their night vision preoperatively so they have a basis for comparison postoperatively. Following LASIK surgery some patients will be aware of increased glare or haloes around lights, especially in the first 3 months after surgery. This tends to occur in patients with night vision problems prior to surgery, and in patients with large corrections (> –7.00 D).” Pupil size as a risk factor for impaired night vision is controversial. (Refer to Schallhorn et al.2) It is rare for a patient to feel completely disabled at night. Night vision problems can also be related to residual nearsightedness or astigmatism. In this case glasses used for night driving may help. Retreatment may also be a consideration.”
“Some patients will achieve significant improvement in night vision following surgery if they were not well corrected before surgery
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