Chapter 16 – Preoperative Evaluation for Refractive Surgery
JOSHUA A. YOUNG
ERNEST W. KORNMEHL
• Preoperative work-up consists of a sequence—screening, preoperative examination, and counseling.
• Important factor that determines the likelihood of success in refractive surgery.
• Improper preoperative evaluation may result in:
• Treatment of patients who should not be treated (e.g., those who have keratoconus).
• Denial of treatment to some who show only transient abnormalities at the time of examination (e.g., corneal distortion because of contact lens wear).
• Unnecessary prolongation of the postoperative course (e.g., patients affected by undiagnosed dry eye).
The purpose of screening is to eliminate patients who are clearly not candidates for refractive surgery. Areas of inquiry may include age and the type and degree of refractive error. Although all excimer lasers perform grossly the same tasks, their approved ranges of photorefractive keratectomy and laser in situ keratomileusis (LASIK) differ. Contact lenses must be removed prior to the preoperative examination (3 weeks for hard or rigid gas-permeable lenses and 7–14 days for soft contact lenses). In addition, patients must be asked to bring copies of old spectacle prescriptions if available or the old spectacles themselves so that refractive stability may be assessed.
The preoperative examination consists of three parts—history, ophthalmic examination, and counseling.
Systemic Contraindications for Keratorefractive Surgery
The medical history interview must include questions about allergies, autoimmune disease, diabetes mellitus, pregnancy, thyroid disease, collagen vascular disorders, and abnormal wound healing ( Box 16-1 ).
Autoimmune history is particularly important. Seiler et al. reported one patient who was found to have unrecognized systemic lupus erythematosus after postoperative complications severe enough to require penetrating keratoplasty. Diabetes mellitus is a contraindication as well. Pregnancy is a contraindication for a number of reasons. First, pregnancy is believed to induce
Systemic Contraindications to Photorefractive Keratectomy and Laser-Assisted In Situ Keratomileusis
PREGNANCY OR NURSING
ABNORMAL WOUND HEALING
INTERFERENCE FROM SYSTEMIC MEDICATIONS
refractive fluctuations. Although Hefetz et al. reported no unexpected outcomes in 11 eyes of eight women who became pregnant shortly after undergoing photorefractive keratectomy (PRK), Sharif reported a greater risk for corneal haze and myopic regression in women who become pregnant within 5 months of PRK. Second, postponement of surgery until after childbirth or weaning avoids fetal exposure (or infant exposure in the case of nursing mothers) to topical and systemic post–refractive surgery medications. Third, refractive surgery is delayed until after childbirth because of possible changes that occur in the tear layer during pregnancy (discussed subsequently). Thyroid disease and related orbitopathy are important in relation to the tear layer as well.
Abnormalities of wound healing, such as keloid formation, may lead to postoperative complications, which include corneal haze. Although anecdotal evidence suggests that keloid formers may not be at greater risk of complications,  it is advisable not to perform PRK on these patients. Anecdotal evidence suggests that keloid formation is not a contraindication to LASIK.
Ophthalmic contraindications ( Table 16-1 ) fall into three categories—disorders that interfere with the tear layer, disorders that themselves may be exacerbated by photoablation, and abnormalities of corneal topography. Herpetic reactivation is a reasonable concern because ultraviolet exposure may initiate dendritic eruption, and the excimer laser, which uses ultraviolet radiation, may provide such a trigger. Indeed, anecdotal reports of herpetic reactivation after photoablation have been
TABLE 16-1 — OPHTHALMIC CONTRAINDICATIONS TO PHOTOREFRACTIVE KERATECTOMY
Ocular surface disease
Mild dry eye
• Lid disorders that affect the tear layer
Severe dry eye
• Keratoconjunctivitis sicca;
• Exposure keratitis;
• Lid disorders that affect the tear layer
Disorders that may be exacerbated by photorefractive keratectomy
Herpes zoster ophthalmicus/herpetic keratitis (if inactive for > 1 year—unproved)
Herpes zoster ophthalmicus/herpetic keratitis (especially if active during the previous 6 months)
Abnormalities of corneal shape
Shape changes induced by contact lens
Mild irregular astigmatism
• Pellucid marginal degeneration
High, irregular astigmatism
Prior ophthalmic surgery that involved the central cornea
Radial keratotomy (unproved)
Penetrating keratoplasty, etc.
Other ophthalmic disorders
Progressive retinal disease
published. Bialasiewicz et al. described a patient who underwent phototherapeutic keratectomy for treatment of a herpetic scar, was noted subsequently to have stromal infiltration, and progressed to descemetocele and eventually to corneal perforation.
Opinions differ, however, as to whether photoablation may be implicated in herpetic reactivation. Fagerholm et al. reported a series of 20 eyes in 20 patients for whom recurrence after photoablation occurred no more frequently than prior to ablation. Another indication that herpetic reactivation may be incidental to excimer exposure is that when reactivation does occur, it often does so several months after treatment. Such recurrences may be related to topical corticosteroid therapy rather than to laser exposure itself.
Experimental work that involved a murine model demonstrated the shedding of virus after photoablation. It is unclear whether this shedding is a result of excimer exposure or a result of mechanical irritation, as suggested by Tervo and Tuunanen. Subsequent work by Dhaliwal et al. with a rabbit model suggests that herpes simplex virus (HSV) shedding occurs following excimer exposure in both surface ablations and LASIK.
Moreover, some evidence suggests that HSV may be spread in the laser plume. Moreira et al. exposed cell monolayers infected with HSV or adenovirus to excimer photoablation and demonstrated viral spread to sentinel dishes. Presence of vacuum aspiration influenced the direction of spread of the virus toward dishes in the direction of the vacuum.  Although it does not demonstrate evidence of spread in the clinical setting, this study raises concerns for the treating physician, staff, and other patients.
Glaucoma may be exacerbated indirectly by PRK. Corticosteroid responders may be difficult to manage after PRK. Although LASIK may be performed in the well-managed glaucoma patient, a decrease in central corneal thickness, resulting from photoablation or otherwise, will result in an apparent reduction in intraocular pressure as measured by applanation. 
Visual field defects have been documented in patients after LASIK.   Barotrauma and ischemia have been suggested as etiologies for post-LASIK optic neuropathy.
Topographic contraindications to PRK include keratoconus, pellucid marginal degeneration, and topographic abnormalities that signify irregular astigmatism. Patients known to have ectatic conditions such as keratoconus and pellucid marginal degeneration must not undergo photoablation for the obvious reason that ablation thins the cornea.
Ocular conditions that interfere with wound healing include previous radial keratotomy, neurotrophic corneas, and dry eye. Prior radial keratotomy is a relative contraindication to PRK and LASIK. Success, as defined by the likelihood of achieving 20/40 (6/12) or better uncorrected visual acuity, is substantially lower in patients who have undergone radial keratotomy before PRK compared with patients who have not undergone refractive surgery previously. However, in the light of anecdotal success in PRK after radial keratotomy, radial keratotomy must remain no more than a relative contraindication. Anecdotal reports exist of success with LASIK after radial keratotomy, but well-controlled studies need to be carried out.
Even in the absence of recurrent corneal erosions, poor adherence of the epithelium resulting from epithelial basement membrane disease may interfere with the production and subsequent healing of the flap after LASIK. Complications associated with epithelial sloughing resulting from microkeratome use in patients with epithelial basement membrane dystrophy include flap distortion, interface epithelial ingrowth, flap keratolysis, and corneal scarring.
The most important disorder of the tear layer is keratoconjunctivitis sicca. Unrecognized dry eye may substantially delay reepithelialization and result in increased postoperative haze after PRK and keratitis after LASIK. An inadequate tear volume may fail to dilute proteolytic enzymes such as plasmin and growth mediators such as epithelial growth factor. Moreover, a decreased tear volume may result in decreased levels of tear immunoglobulins, lactoferrin, and lysozyme and thereby increase the susceptibility of the cornea to infection.
A variety of conditions predispose the patient to dry eye. Hormonal causes of lacrimal insufficiency include pregnancy and menopause. Infectious causes include syphilis, tuberculosis, trachoma, hepatitis B and C, and diffuse infiltrative lymphadenopathy syndrome associated with human immunodeficiency virus. Lymphoma, amyloidosis, hemochromatosis, and sarcoidosis cause dry eye through infiltrative mechanisms. Multiple sclerosis and seventh nerve cranial neuropathies may cause dry eye. Sjögren’s syndrome causes dry eye but is unlikely to remain undetected in the thorough refractive preoperative evaluation. Also, many medications have been implicated in the incitement or worsening of dry eye ( Box 16-2 ).  Depending upon the cause, dry eye is a readily treatable pathology. Seiler and McDonnell  recommend frequent use of nonpreserved artificial tears and temporary or permanent punctal plugs. Patients who have progressive retinal pathologies are also ruled out for refractive surgery. Similarly, patients who have myopic degeneration, uveitis, or visually significant cataracts are not suitable for refractive surgery.
Systemic Medications That May Induce Dry Eye
Family ocular history is important, especially with regard to corneal ectatic disorders, progressive retinal disease, glaucoma, and cataracts.
The preoperative ophthalmic examination consists of determining ocular dominance, pupil size measurement in dim light, manifest and cycloplegic refraction, topography, pachometry, slit-lamp examination, and dilated funduscopy ( Box 16-3 ). Special care is required when manifest refraction is performed, with emphasis on an accurate measurement without accommodation. Proper fogging and binocular balance are central because it is ultimately only the value obtained by refraction that is entered into the excimer. Cycloplegic refraction with 1% cyclopentolate is mandatory because even the most careful refraction may fail to disclose an accommodative component.
A complete slit-lamp examination is necessary; special attention is paid to the lids, conjunctiva, and cornea. Eyelid malpositions, lagophthalmos, proptosis, and other external conditions that predispose the cornea to exposure must be recognized and treated before refractive surgery is attempted. Small interpalpebral fissures should be noted if LASIK is planned because of the difficulty of inserting the suction ring. Blepharitis and meibomian gland dysfunction are treated aggressively before photoablation to reduce the risk of bacterial superinfection, to improve the quality of the tear layer, and to prevent meibomian gland secretions and lash debris from becoming lodged in the interface between the flap and the corneal stroma.
Patients affected by significant corneal neovascularization that extends into the central 7?mm of the cornea are excluded from treatment. Peripheral pannus may be associated with bleeding following the keratectomy. The tear meniscus must have a height of approximately 0.3?mm and the tear-film breakup time must be at least 10 seconds. Equivocal results or history of contact lens intolerance requires the ophthalmologist to perform vital staining (rose bengal) and a tear production test.
An accurate preoperative measure of pupillary diameter is necessary. Pupillometry is performed in both room light and dimmed light. Although a pupillary diameter exceeding 6?mm is not a contraindication to photoablation if the procedure is to be performed with a laser that has large optical diameter capability, modification of the surgical plan is required. Pupil diameters may
Distance with and without correction
Reading with and without correction
Current spectacle correction
Cycloplegic refraction with cyclopentolate 1%
Keratometry (measures central 3?mm)
INTRAOCULAR PRESSURE MEASUREMENT
Gross external examination measurements in bright and dim light
Vital stain (if symptoms warrant)
JONES’ BASAL TEAR SECRETION RATE (IF SYMPTOMS/SIGNS WARRANT)
be assayed by directly measuring the pupil with a Rosenbaum card, although measurements so performed often overestimate pupil size. Pupillometry may also be performed using a hand-held infrared pupillometer. Keratometry is measured to assess the power of the central cornea, to gauge the quality of the mires, and to provide a basis for later intraocular lens calculations. As part of a thorough examination, tonometry is performed to ascertain intraocular pressure.
Dilated funduscopy is performed to identify patients affected by progressive retinal disease; retinal holes, tears, or atypical lattice degeneration; unrecognized diabetic retinopathy; myopic degeneration; and other pathologies that preclude photoablative treatment.
Computerized videokeratography is absolutely essential in the preoperative evaluation of patients for refractive surgery. It is the only way to uncover early or mild keratoconus. The population of patients who seek refractive surgery seems to carry an increased incidence of keratoconus (3–5%), perhaps as much as 10 times that of an expected random sample of myopes. These patients are probably a self-selected group for both keratoconus and dry eye because both pathologies manifest as contact lens intolerance.
It is likely that many patients who exhibit keratoconus-like patterns that are undetectable by other means and cause no symptoms (so-called keratoconus suspects) remain subclinical. Only long-term follow-up differentiates these patients from those who go on to progressive ectasia. However, Seiler and Quurke reported a case of a patient with forme fruste keratoconus progressing to frank ectasia following LASIK. Therefore, these patients should be avoided.
Corneal molding (warpage) is a transient corneal distortion produced primarily by rigid contact lens wear, but it may result from soft contact lens wear as well. Although transient, this distortion may persist for up to 5 months. For this reason, it is advisable for a patient to discontinue contact lens wear before the preoperative examination—for at least 3 weeks for rigid lenses and 2–14 days for soft lens wearers. If topographic examination is suggestive of corneal molding, a longer period of contact lens cessation is warranted until the topography stabilizes.
Pachymetry must be performed prior to LASIK. It is mandatory that there be at least 250?mm of tissue in the bed after ablation. If this important parameter is ignored, the patient is at risk for corneal ectasia and an unstable refraction. Controversy exists as to whether optical pachymetry as provided by the Orbscan device may be substituted for ultrasonic pachymetry. Although optical pachymetry has the advantage of providing an array of corneal thickness measurements throughout the cornea and therefore identifying areas of corneal thinning outside the central cornea, recommendations for minimum bed thickness have been based upon ultrasonic and not optical devices. Furthermore, the Orbscan algorithm seems to produce readings that are consistently higher than those obtained by ultrasonic means. 
Not all patients who meet medical and ophthalmic criteria for refractive surgery are necessarily good candidates for the procedure. Patients must be told that spectacles may be required for certain tasks such as driving at night. After surgery, patients should not expect to obtain perfect uncorrected distance acuity. Those who are dissatisfied with these projections are likely to be dissatisfied after surgery. Presbyopic myopes must be made aware that the removal of distance glasses to achieve a near addition is no longer possible after refractive surgery. However, if the patient’s lifestyle permits and the patient is motivated sufficiently, monovision may be a possibility.
The preoperative evaluation of the patient for refractive surgery is lengthy and must be performed in an unrushed manner. However, it is time well spent because the best treatment for complications and disappointment is avoidance.
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