screen—not just reading. These points cannot be overemphasized for patients with myopia who are approaching age 40 years. Before refractive surgery, these patients can read well with and without their glasses. Some may even read well with their contact lenses. If their eyes are emmetropic after surgery, many will not read well without reading glasses. The patient needs to understand this phenomenon and must be willing to accept this result before undergoing any refractive surgery that aims for emmetropia. In patients who wear glasses, a trial with contact lenses will approximate the patient’s reading ability after surgery.
A discussion of monovision (ie, 1 eye corrected for distance and the other eye for near/intermediate vision) often fits well into the evaluation at this point. The alternative of monovision correction should be discussed with all patients in the age groups approaching or affected by presbyopia. Many patients have successfully used monovision in contact lenses and want it after refractive surgery. Others have never tried it but would like to, and still others have no interest. If a patient has not used monovision before but is interested, the attempted surgical result should first be demonstrated with glasses or temporary contact lenses at near and distance. Generally, the dominant eye is corrected for distance and the nondominant eye to approximately –1.50 to –1.75 D. For most patients, such refraction allows good uncorrected distance and near vision without intolerable anisometropia. Some surgeons prefer a “mini-monovision” procedure, whereby the nearvision eye is corrected to approximately –0.75 D, which allows some near vision with better distance vision and less anisometropia. The exact amount of monovision depends on the desires of the patient. Higher amounts of monovision (up to –2.50 D) can be used successfully in selected patients who want excellent postoperative near vision. However, in some patients with a higher degree of postoperative myopia, improving near vision may lead to unwanted adverse effects of loss of depth perception and anisometropia. It is often advisable to have a patient try monovision with contact lenses before surgery to ensure that distance and near vision as well as stereovision are acceptable and that no muscle imbalance is present, especially with higher degrees of monovision.
Although typically the nondominant eye is corrected for near, some patients prefer that the dominant eye be corrected for near. Of several methods for testing ocular dominance, one of the simplest is to have the patient point to a distant object, such as a small letter on an eye chart, and then close each eye to determine which eye he or she was using when pointing; this is the dominant eye. Another is to have a patient make an “okay sign” with one hand and look at the examiner through the opening.
Examination
Uncorrected Visual Acuity and Manifest and Cycloplegic Refraction
The refractive elements of the preoperative examination are extremely important because they directly determine the amount of surgery to be performed. Visual acuity at distance and near should be measured. The current glasses prescription and visual acuity with those glasses should also be determined, and a manifest refraction should be performed. The sharpest visual acuity with the least amount of minus (“pushing plus”) should be the final endpoint (see BCSC Section 3, Clinical Optics). The duochrome test should not be used as the final endpoint because it tends to overminus patients. Document the best visual acuity obtainable, even if it is better than 20/20. An automated refraction with an autorefractor or wavefront aberrometer may be helpful in providing a starting point for the manifest refraction. A cycloplegic refraction is also necessary; sufficient waiting time must be allowed between the time the patient’s eyes are dilated with appropriate cycloplegic eye drops—
tropicamide, 1%, or cyclopentolate, 1%, is generally used—and the refraction. For full cycloplegia, waiting at least 30 minutes (with tropicamide, 1%) or 60 minutes (with cyclopentolate, 1%) is recommended. The cycloplegic refraction should refine the sphere and not the cylinder from the manifest refraction, as it is done to neutralize accommodation. For eyes with greater than 5.00 D of refractive error, a vertex distance measurement should be performed to obtain the most accurate refraction. When the difference between the manifest and cycloplegic refractions is large (eg, >0.50 D), a postcycloplegic manifest refraction may be helpful to recheck the original. In patients with myopia, such a large difference is often caused by an overminused manifest refraction. In patients with hyperopia, substantial latent hyperopia may be present, in which case the surgeon and patient need to decide exactly how much hyperopia to treat. If there is significant latent hyperopia, a pushedplus spectacle or contact lens correction can be worn for several weeks or months preoperatively to reduce the postoperative adjustment from treating the true refraction.
Refractive surgeons have their own preferences for whether to program the laser using the manifest or cycloplegic refraction, based on their individual nomogram and technique and on the patient’s age. Many surgeons plan their laser input according to the manifest refraction, especially for younger patients, if that refraction has been performed with a careful pushed-plus technique.
Pupillary Examination
After the manifest refraction (but before dilating eye drops are administered), the external and anterior segment examinations are performed. Specific attention should be given to the pupillary examination; the pupil size should be evaluated in bright room light and under dim illumination, and the surgeon should look for any afferent pupillary defect. A variety of techniques are available for measuring pupil size in dim illumination, including use of a near card with pupil sizes on the edge (with the patient fixating at distance), or a pupillometer. The dim-light measurement should be taken using an amount of light entering the eye that closely approximates the amount entering during normal nighttime activities such as night driving; it should not necessarily be done under completely dark conditions.
Pupil size measurements should be standardized as much as possible. Large pupil size may be a risk factor for postoperative glare and halo symptoms after refractive surgery. Measuring the lowlight pupil diameter preoperatively and using that measurement to direct surgery remains a controversial approach. Conventional wisdom suggests that the optical zone should be larger than the pupil diameter to minimize vision disturbances such as glare and halos. Recent evidence, however, does not support an association between preoperative pupil size and an increased incidence of either glare or halo complaints 1 year postoperatively. It is not clear, therefore, that pupil size can be used to predict which patients are more likely to have such symptoms. The size of the effective optical zone— which is related to the ablation profile and the level of refractive error—may be more important in minimizing visual adverse effects than is the low-light pupil diameter.
When asked, patients often note that they had glare under dim-light conditions even before undergoing refractive surgery. Thus, it is important that patients become aware of their glare and halo symptoms preoperatively, as this knowledge may minimize postoperative complaints or misunderstanding.
Chan A, Manche EE. Effect of preoperative pupil size on quality of vision after wavefront-guided LASIK. Ophthalmology. 2011;118(4):736–741. Epub 2010 Nov 20.
Edwards JD, Burka JM, Bower KS, Stutzman RD, Sediq DA, Rabin JC. Effect of brimonidine tartrate 0.15% on night-vision difficulty and contrast testing after refractive surgery. J Cataract Refract Surg. 2008;34(9):1538–1541.
Pop M, Payette Y. Risk factors for night vision complaints after LASIK for myopia. Ophthalmology. 2004;111(1):3–10.
Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, Bourque LB. Pupil size and quality of vision after LASIK. Ophthalmology. 2003;110(8):1606– 1614.
Schmidt GW, Yoon M, McGwin G, Lee PP, McLeod SD. Evaluation of the relationship between ablation diameter, pupil size, and visual function with visionspecific quality-of-life measures after laser in situ keratomileusis. Arch Ophthalmol. 2007;125(8):1037–1042.
Ocular Motility, Confrontation Fields, and Ocular Anatomy
Ocular motility should also be evaluated. In patients with asymptomatic tropia or phoria, symptoms may develop after refractive surgery if the change in refraction causes the motility status to break down. If there is a history of strabismus (see Chapter 10) or a concern about ocular alignment postoperatively, a trial with contact lenses before surgery should be considered. A sensory motor evaluation can be obtained preoperatively if strabismus is an issue. Confrontation fields should be considered as well, if clinically indicated.
The general anatomy of the orbits should also be assessed. Patients with small palpebral fissures and/or large brows may not be ideal candidates for LASIK or epipolis LASIK (epi-LASIK) because there may be inadequate exposure and difficulty in achieving suction with the microkeratome or laser suction ring.
Intraocular Pressure
The intraocular pressure (IOP) should be checked after the manifest refraction is completed and corneal topography measurements are taken. Patients with glaucoma (see Chapter 10) should be advised that during certain refractive surgery procedures the IOP is dramatically elevated, potentially aggravating optic nerve damage. Also, topical corticosteroids are used after most refractive surgery procedures and, after a surface ablation procedure, may be used for months. Long-term use of topical corticosteroids may cause marked elevation of IOP in corticosteroid responders.
Samuelson TW. Refractive surgery in glaucoma. Curr Opin Ophthalmol. 2004;15(2):112–118.
Slit-Lamp Examination
A complete slit-lamp examination of the eyelids and anterior segment should be performed. The conjunctiva should be examined specifically for conjunctival scarring, which may cause problems with microkeratome suction. The cornea should be evaluated for surface abnormalities such as decreased tear breakup time (Fig 2-1) and punctate epithelial erosions (Fig 2-2). Significant blepharitis (Fig 2-3), meibomitis, and dry eye syndrome should be addressed before refractive surgery, as they are associated with increased postoperative discomfort and decreased vision, and dry eye symptoms frequently increase postoperatively. A careful examination for epithelial basement membrane dystrophy (Fig 2-4) is required, because its presence increases the risk of flap complications during LASIK. Patients with epithelial basement membrane dystrophy are not ideal candidates for LASIK and may be better candidates for a surface ablation procedure. Signs of keratoconus, such as corneal thinning and steepening, may also be found. Keratoconus is typically a contraindication to incisional or ablative refractive surgery (see Chapter 10). The endothelium should be examined carefully for signs of cornea guttata and Fuchs and other dystrophies. Poor visual results have been reported in patients with cornea guttata and a family history of Fuchs dystrophy. Corneal edema is generally considered a contra-indication to refractive surgery. The deposits of granular and Avellino corneal dystrophies may increase substantially in size and number in the flap interface after LASIK, resulting in poor vision.
Figure 2-1 Slit-lamp photograph showing decreased tear breakup time. After instillation of fluorescein dye, the patient keeps the eye open for 10 seconds, and the tear film is examined with cobalt blue light. Breaks, or dry spots, in the tear film (arrows) are visible in this image. Punctate epithelial erosions are also present.
Figure 2-2 Slit-lamp photograph, showing punctate epithelial erosions. Inferior punctate fluorescein staining is noted in this image from a patient with moderately dry eyes.
Figure 2-3 Example of blepharitis. Moderate crusting at the base of the lashes is shown in this image of a patient with
seborrheic blepharitis. (Courtesy of Christopher J. Rapuano, MD.)