5
LASEK Preoperative Evaluation
Chun Chen Chen, MD
Taipei Municipal Jen-Ai Hospital,
National Yang-Ming University
Taipei, Taiwan
Dimitri T.Azar, MD
Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute,
Harvard Medical School
Boston, MA
GENERAL MEDICAL HISTORY
The general history of the patient is helpful in identifying systemic pathologies that may be a contraindication to the laser subepithelial keratomileusis (LASEK) procedure. Relative systemic contraindications that theoretically might affect healing and influence the refractive outcome include: pregnancy, diabetes mellitus, immunocompromise, collagen disorders, e.g., systemic lupus erythematosus (SLE) and rheumatoid arthritis, allergies or atopia, systemic infections (HIV or tuberculosis), and systemic medication of certain drugs, such as steroids and hormone replacement therapy.
OCULAR HISTORY
This should include previous ocular surgery, orthoptic treatment, and refractive surgery. In particular, an accurate contact lens history should be ascertained when the lenses were last worn, the type of contact lens, the ongoing wearing success or not, and the reasons of discontinuation of contact lens wear, which are all equally essential points.
Ocular surface abnormalities resulting from Sjögren’s disease, alkali burn, or ocular cicatricial pemphigoid are absolute contraindications of LASEK. Moderate to severe dry eye syndromes resulting in surface abnormalities are relative contraindications to refractive surgery (1,2). Punctum occlusion and tear replacement therapy are often necessary to stabilize the dry eye condition before surgery. A history of neurotrophic corneal ulcers, herpes zoster ophthalmicus, or nonhealing epithelial defects makes the patients ineligible for refractive surgery. A history of herpes simplex virus (HSV) keratitis represents another relative contraindication to refractive surgery. Photorefractive keratectomy (PRK) and phototherapeutic keratectomy (PTK) performed on patients with a history of HSV have resulted in cases of reactivation of latent virus (3). Oral acyclovir given in the peri-operative period may be beneficial in preventing recurrence of the disease.
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SOCIAL AND OCCUPATIONAL HISTORY
Evaluating the patient’s vocational and recreational refractive needs is important for surgical goals and planning. Patients should be informed of the possible complication of refractive surgery and the best-corrected visual acuity may be compromised. Those whose careers have strict requirement of visual acuity should check with their employers before undergoing keratorefractive surgery. Patients of presbyopic age may benefit from monovision (4,5), whereas younger patients (<35–40 years of age) are usually not tolerant of this approach.
VISUAL ACUITY
Visual acuity (VA) is usually recorded by Snellen notation, i.e., 6/12 or 20/40, depending on the testing distance of 6 meters in the UK or Australia and 20 feet in the United States, respectively (6). Early Treatment Diabetic Retinopathy Study (ETDRS) charts are valuable for conducting LASEK studies (Fig. 1). Documentation of uncorrected and best spectacle corrected visual acuity at near and distance is useful for evaluating the efficacy and predictability of the refractive surgery. Severe and extreme myopia is associated with reduced best spectacle corrected visual acuity, which may be different between spectacle correction and contact lens correction. High diopters of myopia and astigmatism may enjoy a level of visual acuity in rigid gas permeable contact lens that may be impossible to reach by refractive surgery. Myopic patients, who are 45 to 50 years of age, need to understand the implications of opting for full distance. It is important to document and discuss these details with the patients in assessing postoperative outcomes, and in achieving high levels of patient’s satisfaction.
Refraction
A definite, accurate refraction is obviously essential and is the most critical assessment in respect to outcome, because the most accurate laser system cannot improve on a poor refraction.
A cycloplegic refraction is important to ensure a significant accommodative component is not evident (7). Cycloplegia is conducted by instilling one drop of cyclopentolate three times (at 10-minute intervals). A cycloplegic refraction is performed 30 minutes after the last drop is instilled. Alternatively, 1% tropicamide can be instilled at least three times (again, at 10-minute intervals) and refraction performed 15 minutes after the last dose. The cycloplegic refraction is mandatory to prevent overcorrecting the patient, and it should be performed with retinoscopy and then subjective refinement. In some cases, severe ametropia associated with alterations of the posterior pole (myopic staphyloma) makes retinoscopy difficult.
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Figure 1 ETDRS visual acuity chart. This chart is valuable for LASEK studies, although it may be less convenient than the Snellen chart for routine measurements of visual acuity. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
Objective Refraction
In most cases, the manifest refraction is the one selected for the refractive surgery correction. It must therefore be carefully performed so that it provides the best visual acuity with the least amount of minus correction. One must be extremely careful not to
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over-minus the patient. The refraction should be doubly checked in the trial frame, which should be well positioned with careful vertex distance measurement, especially as the amount of myopia increases. The first measurement to be taken is the interpupillary distance (PD), and then the trial frame or the phoropter PD needs to be adjusted accordingly (6). Ensure that the trial frame fits properly or that the patient always keeps the head against the phoropter. The horizontal orientation between both trial frame or phoropter head and the patient’s eye is important for astigmatic axis assessment. The back vertex distance (BVD), the distance between the eye and the back of the trial lens in situ, needs to be measured in a trial frame for spherical equivalent over minus 4.0 DS.
Streak retinoscopy and autorefractors (Fig. 2) are objective methods of determination of refractive error. During the refraction, to avoid unwanted accommodation, the patient should be instructed to look at a fixation light in the distance (6 meters/20 feet equivalent), and the room illumination should be low. In aphasia or strabismus, the fellow eye is occluded; otherwise, the fellow eye is fogged until the visual acuity is 6/12 (20/40) or poorer. For the eye undergoing retinoscopy, it is desirable to neutralize any “with movement” with positive spheres before neutralizing the “against movement” with negative cylinders to prevent stimulation of accommodation. The refinement of axis of the corrective cylinder is accomplished through the observation of the break, skew, or straddling phenomena. After the refinement of the axis of the cylinder, the power of the cylinder is refined by adding a small amount of minus sphere to obtain the “with movement.” The cylinder power is then adjust so that the “with movement” has the same quality in all meridians. Occlude one eye at the end of the objective assessment and adjust the spherical component within the trial frame to compensate for the working (refraction) distance.
Subjective Refraction
Jackson Cross-Cylinder Technique
To refine the cylinder component there are two widely used and well-described methods using either the Jackson cross-cylinder or the fan and block technique. A cross-cylinder incorporates two lens of equal power with opposite signs; therefore, the mean sphere power is zero. It is used for subjective refinement of axis and power of the cylinder. The axis of the cylinder is refined by rotating the cross cylinder, as led by the flip choices, with the axes of the Jackson cross-cylinder straddling the axis of the corrective cylinder
(8). After the determination of the axis, the cross-cylinder is turned 45 degrees, and the power of the cylinder is refined. When the power of cylinder is changed, then adjustment of the spherical component is also needed. The cross-cylinder technique requires for the circle of least confusion to be focused on the retina.
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Figure 2 Automated refractors are helpful in obtaining an approximate idea of the patient’s refractive error. They should not be used as the sole basis of LASEK treatments. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
The spherical component of the objective refraction needs to be confirmed. This power is adjusted by requesting the patient to look at a letter on the last line of distinct vision and to reply if the letter improves in clarity or reduces with the addition of a powered lens. To ensure that accommodation is not stimulated, add the positive lens in +0.25 diopter (D) step. If a reduction of visual acuity occurred, then remove the plus lens. To avoid the over-correction of myopia, the examiner can ask the patient whether the image is becoming smaller or sharper or perform the duochrome (bichromatic) test.
Red-Green (Duochrome, Bichromatic) Test
The red-green (duochrome, bichromatic) test may be used to study the optimal spherical correction that has already been refined to within 1 D of emmetropia (8). It is based on the chromatic aberration; when a pencil of light is rendered convergent by a plus lens, the red light is focused behind green light because of longer wavelength. While fogged with the plus lens, the patient is asked to gaze at letters or circles on a half-red, half-green
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background. The letters on the red side should become clearer. Plus lenses are removed in 0.25 D step until the letters on two backgrounds become equal. At the endpoint of subjective refraction, place a +1.00 DS lens into the trial frame and record the VA obtained. This is called “fogging” and the +1.0 DS lens is the “fogging lens.” The VA should “blur back,” i.e., be reduced to approximately 6/12 (20/40) if the patient’s correctable VA was approximately 6/5 (20/15). If the patient can still see the original line or that above with “fogging,” the patient has too much negative sphere incorporated into the subjective prescription and, therefore, the letters on the green background will be clear while the letters on the red will be blurred.
Binocular Balancing
The final step of subjective refraction is the achievement of equal and minimal accommodative tone in both eyes. The tests of binocular balancing require that correctable visual acuity of both eyes is essentially equal. The most sensitive test of binocular balance is the prism dissociation method. Four or five prism diopters of vertical prism are placed before one eye. After fogging of both eyes with +1.0 D sphere, the sharpness of the fogged images (6/12 or 20/40 line) is compared. Plus sphere is added in +0.25 D step in one eye and then in the other eye. If the eyes are balanced, the patient will report that the eye with the additional +0.25 D sphere will be more blurred. After a balance of the binocular images is established, remove the prism and unfog the binocular until the maximal visual acuity is obtained. The other commonly used test of binocular balance is fogging method. With the +2.0 D sphere placed before each eye, the patient is asked to look at the letter on the 6/20 (20/100) or 6/20 (20/70) line. While a −0.25 D sphere is placed in front of one eye and then the other, the patient will be able to identify the image of the eye with the −0.25 D sphere more clearly. If the eyes are not in balance, the sphere should be added or subtracted in 0.25 D step until balance is achieved.
Refinement of Cylindrical Correction
Frequently, the magnitude and axis of astigmatism documented by the aforementioned technique are different from the data obtained by computerized videokeratography (CVK), keratometry, and autorefraction. In such a situation, it is helpful to repeat the subjective refraction according to the axis and power suggested by the topographic power. Lenticular astigmatism should be suspected if there are significant disparities between the topography and subjective findings. Lenticular astigmatism accounts for the difference between corneal astigmatism and total astigmatism. It can be produced by lens surface or by tilting or decentration of the spectacle lens with respect to cornea. If the resultant ocular astigmatism axis is different to the corneal axis, then the former axis direction will have been created in accordance with the theory of obliquely crossed cylinders.
External Eye Examination
External examination should focus on the globe position, eyelid, eyelash, and lacrimal apparati. In eyes with prominent brow, narrow palpebral fissure, or deep-set eyes, the
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surgeon should be prepared to alter technique and perform instrumentation to obtain sufficient exposure of the eyeball. The patient should be informed in advance if these procedures (e.g., lateral canthotomy) are possible. Any lid abnormalities, such as lagophthalmos, entropin, ectropin, and trichiasis, can cause problems with corneal exposure and ocular surface instability. Blepharitis, canaliculitis, and dacryocystitis can predispose patients to infection in the peri-operative period. Secretions of the meibomian gland may be responsible for sands of Sahara syndrome. An excessively oily tear film can interfere with the uniformity of the ablation. Those problems should be recognized and treated before planning surgery.
Biomicroscopic Examination
The slit lamp examination allows detailed examination of conjunctiva, corneal scars, corneal neovascularization, kerato-conjunctivitis sicca, superficial corneal dystrophy, keratoconus, pterygium, pterygoid, irregular epithelium, evidence of recurrent corneal erosion, filtering bleb, redundant conjunctiva, anterior uveitis, keratitis, and lenticular clarity.
Examination of the conjunctiva should detect any scarring from previous trauma, surgery, inflammatory disease, or infection, or any conjunctival lesions. The presence of conjunctival pathology can potentially interfere with proper lid closure and create corneal dellen and other ocular surface abnormalities.
The cornea should be examined for evidence of any epithelial, stroma, or endothelial pathology. Corneal neovascularization is frequently observed in long-term contact lens wearers and is commonly seen at the superior limbus. History of recurrent corneal erosion, basement membrane dystrophy, and dry eye syndrome can create epithelial defect intraoperatively and postoperatively, which increase the incidence of epithelial ingrowth, postoperative infection, and prolong recovery. The tear film should be observed and tear break-up time recorded. If tear film or tear break-up time decreases, further evaluation, including Schirmer testing, is indicated. Corneal sensitivity should be tested, and if decreased, potential causes of neurotrophic corneal disease should be searched.
The corneal stroma should be examined for thickness and clarity. An increase in corneal thickness should prompt the examiner to evaluate endothelial cell function. Corneal thinning may be caused by keratoconus, pellucid degeneration, previous infection with loss of stroma, inflammatory disease, or trauma. Stromal opacity with neovascularization may indicate previous herpetic infection or other chronic ocular surface inflammatory processes.
The corneal endothelium should be assessed for the presence of any endothelial changes such as endothelial dystrophies, guttata, and ruptures in the Descemets membrane, which is contraindicated to perform intrastromal laser ablation.
Anterior chamber depth and inflammation should be evaluated. The presence of any iris abnormality may indicate previous herpes zoster infection, trauma, anterior segment dysgenesis syndrome, or uveitis.
The lens should be checked for any evidence of cataract formation. With the exception of very small, visually insignificant congenital cataracts, lens opacities represent an absolute contraindication to refractive surgery.
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Corneal Aesthesiometry
Corneal aesthesiometry measures sensitivity of the cornea. An empirical measurement can be made by placing a thread of cotton in contact with the cornea, causing bleparospasm. The absence or slowness of the reflex indicates corneal aesthesia or hypoesthesia. There are specific instruments (keratoesthesiometers) for the quantitative measurement of corneal anesthesia (e.g., Cochet-Bonnet model or Frey’s model).
The center of the cornea is more sensitive than the peripheral areas. The filament of the keratoesthesiometer is perceived by the central cornea when it exerts a pressure of 10 to 12 mg/mm2, and by the peripheral cornea when it exerts pressure of 16 to 18 mg/ mm2. Contact lens will reduce the corneal sensitivity. Besides, corneal hypoesthesia is subject to all the complications associated with dry eyes.
Fundus Examination
A detailed fundoscopic examination should be performed to detect any evidence of macular or retinal pathology that could potentially affect visual acuity. Myopic macular degenera-tion, posterior staphyloma, peripheral retinal lesions (e.g., holes, tears), optic nerve pathology, chorioretinopathy, and posterior vitreous detachment should be documented by chart, photography, or angiography and then discussed with the patient. Any retinal or macular pathology that requires further treatment should be referred preoperatively for management. All patients should be informed that the risk of myopic retinal detachment still exists after refractive surgery and annual retinal examination is required (11,12).
Tonometry
Intraocular pressure should be measured to detect ocular hypertension or pressure status in glaucoma patients (Fig. 3). Patients with ocular hypertension who plan to undergo LASEK should be aware of the risk or steroid response in the postoperative period that may necessitate anti-glaucoma medication. In glaucoma patients, better control of intraocular pressure should be attained before LASEK.
Pupil Size
Pupil size is theoretically important in the optical quality of the retinal image and therefore visual performance (13–16). Optical aberrations generally increase with increasing pupil size (17). Aberrations can misdirect light into the eye and can result in symptoms such as glare and haze (18). After refractive surgery, visual quality can be significantly influenced in those patients with large pupil when the pupil diameter is larger than the ablation zone or the level of treatment is higher (19,20).
Pupil size should be evaluated under photopic and mesopic lighting conditions. The pupil diameter can be measured by several methods. The Colvard pupillometer (Fig. 4), developed with Matthew Colvard by Oasis Medical, uses light-amplification technology (21). The levels of illumination are controlled to be 250 to 300 lux and 3 lux, which simulate the daytime (photopic) and nighttime (scotopic) conditions, respectively. The
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examinations should be performed after keeping the patient in the room for at least 30 seconds and the fellow eye open. The pupillometer was placed in front of one eye and adjusted before and after until the pupil was in sharp focus through the viewing screen. The other options include the Rosenbaum pupil caliper, some auto-refractometers, and infrared television camera connected to a monitor (10).
Ocular Dominance
Ocular dominance can be established by history or distance fixation test. Examiners can ask the patients about their preferred or shooting eye when looking through the lens or camera. The dominant eye generally is identified by use of sighting dominance tests. One of the more common tests is the “hole test,” for which the patient is asked to frame an object through a hole formed by the patient’s outstretched hands (22). When the patient constricted the size of the hole by hand, the eye that continued to align with the object and the hole was considered the dominant eye.
Figure 3 A pheumatonometer is used to check the intraocular pressure after application of the suction ring. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
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Figure 4 Colvard pupillometer. Measurement can be optimized by controlling ambient illumination during pupil measurements. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
Understanding the dominance of the eye helps decide the priority of treatment. The basis for treating the nondominant eye first is that the unexpected visual problems (fluctuations, glare, and halo) will be less problematic for the patient if the dominant eye is still functioning normally in the early postoperative period. This also allows the surgeon to assess the effects of wound healing and the predictability in the nondominant eye, which may provide important information for planning the surgery on the dominant eye. Many patients feel more comfortable with having their nondominant eye treated first when no contraindications are evident. In those patients who wish to achieve monovision, dominant eyes will be conventionally corrected for distance (22).
Orthoptic Examination
Motility testing includes examination of ductions, versions, and measurement of any tropias or phorias. This is useful for evaluating binocular vision and potential postoperative diplopia. Any history or finding that suggests amblyopia should also be carefully documented.
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Corneal Topography
Corneal topography is now considered an integral component of preoperative evaluation of the refractive patient. Corneal topography can be used to detect regular and irregular astigmatism, corneal warpage from contact lens wear, or compressive lid lesions, clinical and preclinical or forme fruste keratoconus, pellucid marginal degeneration, and postoperative refractive effects of refractive surgery. Corneal topography is also helpful in determining refractive stability when used as an adjunct to manifest and cycloplegic refraction.
Methods of measuring corneal topography fall into two broad categories: reflectionbased methods and projection-based methods. Examples of reflection-based topography include keratometry (Fig. 5) and videokeratoscopes (Fig. 6). The computer-assisted video-keratoscopy uses a collimating cone to reflect 25 or 30 rings off the corneal surface (23). These reflected rings yield as many as 8,000 data points for computer analysis. This technique detects curvature and refractive power of the anterior corneal surface. However, corneal elevation cannot be calculated from measurement of slope alone. New topography systems based on the principle of projection are becoming more widely used in clinical practice. These devices include slit photography, rasterstereography, moiré interference, and laser interferometry. The Orbscan corneal topography system measures anterior and posterior corneal elevation (relative to best-fit sphere), surface curvature, and corneal thickness by a scanning optical slit device (Fig. 7). The optical acquisition head scans the eye using light slits that are projected at a 45-degree angle (24). Twenty slits are projected sequentially on the eye from the left and twenty slits from the right side for a total of forty slits. The instrument’s software analyses up to 240 data points per slit and calculates the axial curvature (mm or D) of the anterior and posterior corneal surfaces. It also calculates the elevation of the anterior and posterior surface of the cornea as well as the corneal thickness of the entire cornea.
Thirty-three percent of patients presenting for the surgical correction of myopia have abnormal corneal topographic patterns (25). This has been found to be caused by keratoconus in 6% of patients and corneal warpage in 38% of contact lens wearers (25). Topography maps in both clinical and preclinical (forme fruste) keratoconus demonstrate cone-like or asymmetric bowtie-like steepening, usually inferiorly. There is a subgroup of patients who present the typical topographic pattern of keratoconus but good spectaclecorrected acuity and a normal biomicroscopic appearance, so-called keratoconus suspects. It is uncertain whether this represents a forme-fruste or keratoconus or a normal variant. Many topographic patterns can result from contact lens-induced corneal warpage, but they tend to comprise flattening in the area of lens bearing, with possible adjacent steepening. After the cessation of lens wearing, the cornea tends to return to its former shape, with the greatest changes occurring early. In contact lens wearers, it is advisable to perform the topography only after the lens has been discontinued for at least 2 weeks (soft lenses) or 4 weeks (hard or semi-rigid lenses). If abnormalities persist after the cessation of lens wearing, topographic examinations should be repeated at intervals until the corneal shape has normalized or stabilized.
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Figure 5 Manual keratometer. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
Figure 6 Compact placido-based corneal topographical unit. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
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Figure 7 An elevation-based topographical unit is useful in detecting substantial changes in the posterior corneal surface and in measuring corneal pachymetry. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
Pachymetry
Pachymetry is an invaluable tool in the measurement of corneal thickness (Fig. 8). It is very helpful to understand the corneal thickness preoperatively and assess the amount of correction attainable. Care should be taken in disinfection of pachymetry probe if pachyme-try is applied intraoperatively.
Types of pachymetry include optical, ultrasound, and scanning laser. The most common method of pachymetry is ultrasound. Ultrasonic pachymeters provide highly repeatable results with minimal variations between observers. However, if there is any opacity or pathologic change of the cornea, optical pachymetry is recommended, because it will generate further indication of the thickness of the central, paracentral, and peripheral corneal regions. This measurement is essential in patients with keratoconus. There are some factors that may influence the predictability of pachymetry, such as chronic contact lens wearer, excessive wet cornea, and topical anesthesia.
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Contrast Sensitivity
Halo, glare, and visual disturbances at night can happen even though the patients have good visual acuity after refractive surgery (26,27). The daily activity confronts the individ-
Figure 8 Ultrasonic pachymetry. To be able to measure intraoperative corneal pachymetry, the machine may require standardization in the range of 200 µm. (From Ang RT, Azar DT. Adjunctive Instrumentation in LASIK. In: Azar DT, Koch DD, eds. LASIK: Fundamentals, Surgical Techniques, and Complications. New York, NY: Marcel Dekker, 2003.)
ual with an ever-changing set of visual targets, luminances, and contrast that require rapid visual interpretation. Snellen testing of visual acuity is performed only at high contrast. Contrast sensitivity testing evaluates the patient’s ability to perceive a variety of coarse, intermediate, or fine details at differing contrast relative to the background. Therefore, contrast sensitivity seeks to objectively assess the equivalent of the patient’s visual function in the real world.
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Contrast sensitivity testing could be performed by two different optotypes: gradings (sinusoidal and square wave) and standard Snellen letters. Currently, the letter optotype contrast charts designed by Terry, Pelli-Robson, and Regan are more reproducible, sensitive, and specific and have become clinical alternatives to sine wave gratings. The Regan charts present letter targets of different sizes at varied contrast sensitivity, which can be used to establish a true contrast sensitivity function (CSF) curve in the eye. In contrast, Terry and Pelli-Robson charts offer only one size of letter targets with decreased contrast on each successive line. Furthermore, glare disability could reduce the contrast sensitivity of the visual system. More recently, the combinations of brightness acuity tester (BAT), as a glare source, with Regan or Pelli-Robson contrast sensitivity charts have been required by the U.S. Food and Drug Administration as part of the investigational clinical studies of refractive devices.
Impairment of contrast sensitivity function could be found in cataract, glaucoma, optic neuritis, and amblyopia patients. Recent studies have demonstrated the decrease in lowcontrast sensitivity in the patients after PRK and laser in situ keratomileusis (LASIK). Persistent impairment of contrast sensitivity under low-contrast conditions may be found in myopic patients when the level of the treatment is greater than 6.0 D or the ablation zone is smaller (19,20,28). The loss of contrast sensitivity in darkness may be caused by optical aberration, the change in the anterior curvature or posterior surface, and the light scattering of proliferating cells, activated keratocytes, and extracellular matrix (29–33). The measurement of contrast sensitivity function can not only provide the adjunctive information of visual function but also offer a preoperative baseline. All patients should be informed of the possibility of decreased contrast sensitivity after refractive surgery.
Informed Consent
Informed consent should include apprising the patient of surgical and nonsurgical refractive options, the risks, benefits, side effects, and expected outcome of the procedure, and a discussion of enhancement procedure. It is important to address the patient expectations and provide a realistic probability of outcome after surgery. The aim of the refractive surgery is achieving the best vision possible in the safest most conservative way. It is possible to wear spectacles for demanding fine visual tasks, including night driving.
The patient is required to read and sign the consent to acknowledge comprehension. There should be ample opportunity during the discussion for the patient to ask questions. All the discussed information should be accurately documented in the patient file. The necessity for close and long-term follow-up and continued dilated retinal examinations, especially for those with high myopia, should be emphasized in the consent.
CONCLUSIONS
The evaluation of LASEK includes recording a thorough history, performing a complete clinical ophthalmologic examination, using appropriate preoperative tests, and obtaining informed consent for the surgical procedure. The patients should be aware of the expected level of success, the timescale of visual recovery, and possible complications
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that may occur. A stringent preoperative assessment is likely to pay considerable dividends to both the patient and surgeon in the long-run.
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