Introduction
As refractive surgery has evolved from the controversial to the routine, more patients want to decrease their dependence on glasses. Laser in situ keratomileusis (LASIK) is a very common refractive procedure; approximately 596,000 LASIK surgeries were done in the United States in 2015, and the number is expected to increase to almost 720,000 by the year 2020. Ophthalmologists are increasingly confronted with refractive surgical candidates who also have ocular or systemic disease. In such cases, the ophthalmologist must determine whether refractive surgery poses an unacceptable risk. However, the evaluation of patients for corneal refractive surgery has changed considerably in recent years. We have a better understanding of new refractive surgery technologies, such as the wavefront sensor, as well as greater experience with the intricacies of the excimer laser. This has allowed us to clarify issues of patient candidacy as well as to measure and subsequently treat subtle imperfections of vision. Two aspects of refractive surgery make it a unique surgical procedure necessitating a novel approach to patient selection and preoperative evaluation. First, the eye to be operated on is generally healthy. Second, success is ultimately defined by patient satisfaction, an outcome comprising both objective and subjective patient perceptions.
Philosophical Issues
Increased patient interest and evolving attitudes toward refractive surgery within the profession now make it important that all ophthalmologists be conversant with the complete menu of surgical and nonsurgical options for the ametropic patient so that they can properly counsel their patients regarding the advisability and the risks and benefits of each of these procedures. Although some surgeons may philosophically advise against any type of surgical intervention in an otherwise healthy eye, it remains the ophthalmologist’s responsibility to afford considered information and advice to potential refractive surgery patients.
Motivations for surgery are largely unchanged, with independence from spectacles and contact lenses during leisure time being the most common reason for consultation. Law enforcement, emergency services employees, and military recruits are undergoing refractive surgery procedures in increasing numbers to avoid the limitations of wearing spectacles or contact lenses in emergency situations.
Although all forms of refractive surgery pose inherent risks to the healthy eye, other traditional forms of optical correction are not without potential problems. Contact lens wear is a source of morbidity, with problems ranging from minimal discomfort to sight-threatening infections. Giant papillary conjunctivitis, sequelae of corneal hypoxia, sterile infiltration, and microbial keratitis may all complicate contact lens wear, precluding their use in many patients. Several extensive and comprehensive studies have been conducted on the complications caused by contact lens wear. In one well-controlled study, users of extended-wear lenses had a 10- to 15-fold greater risk of ulcerative keratitis than did users of daily-wear soft lenses. In another study, the risk of keratitis was reported to increase fourfold when daily disposable contact lens use was extended to occasional overnight (less often than one night per week) use. Stapleton et al. also reported that the wearing of disposable contact lenses appeared to be associated with the lowest risk of microbial keratitis, adding that age is not associated with the severity of the keratitis (age 15–24 vs. 25–54 vs. 55–64). However, younger age (<25 years) and older age (>50 years) were reported to be at significantly greater risk of developing corneal infiltrates in a 1-year prospective study of 6245 wearers of overnight silicone hydrogel lenses. It was even reported that there was a 5% greater risk of developing contact lens–related complications for every additional year of a patient’s age. In this study of overnight silicone hydrogel lenses, 2.5% of the infiltrates were observed to be lens-related. In a related article, the annual incidence of ulcerative keratitis was described as 20.9 per 10,000 wearers when using extended-wear soft contact lenses and 4.1 per 10,000 wearers when using daily-wear soft contact lenses. Some cases of hospital-based microbial keratitis have also been reported in pediatric patients in Hong-Kong and Taiwan, although reports of these kinds of adverse events are rare in the United States and Europe.
Clearly refractive surgical procedures are not without risk, but patients who are using contact lenses are also ultimately accepting a degree of risk. Thus the philosophical debate regarding refractive surgery is not simply one of whether it is appropriate to operate on an otherwise healthy eye. Rather, specific patient circumstances must be carefully considered in order for both the ophthalmologist and the patient to arrive at an appropriate informed decision based on the risks and benefits of the available treatment options.
Guidelines for Patient Selection
As experience with refractive surgery has improved, insight has been gained into the absolute and relative contraindications associated with these procedures. Ideally a prospective patient should have an entirely normal eye with an appropriate refractive error. However, patients often request treatment of eyes having problems for which surgery might be contraindicated.
Absolute Contraindications
Although advice regarding the propriety of refractive surgery must always be individualized to each patient’s risk-benefit ratio, the following situations include those in which refractive surgery is best avoided. Patients with poorly controlled systemic immunologic disorders such as rheumatoid arthritis, systemic lupus erythematosus, polyarteritis nodosa, and other collagen vascular diseases are at risk of inflammatory and wound-healing sequelae that may cause severe corneal complications. Refractive surgery in such patients is not advised. Contraindications may also derive from the health of the eye itself. Patients with severe dry eye syndromes―including those with conjunctival cicatrizing disorders like Stevens-Johnson syndrome, ocular cicatricial pemphigoid, and a chemically burned ocular surface―are poor candidates because of wound-healing problems that may supervene following surgery.
Patients with keratoconus and other ectatic corneal dystrophies should be identified preoperatively. Such patients may frequently present to the refractive surgical practice because of their poor vision with optical correction. Because the optical and physical effects of refractive procedures and the long-term prognoses are unclear in these patients, most refractive surgery is contraindicated in such situations. One exception to this rule might be consideration of insertion of intracorneal ring segments in patients with keratoconus who suffer contact lens intolerance or where a corneal transplant is inevitable; intracorneal ring segments in this situation have delayed but not prevented progression to corneal transplant. Patients with irregular astigmatism in the absence of keratoconus or ectasia should be managed with caution. The advent of wavefront sensors and the ability to custom reshape the cornea with the excimer laser has allowed some of these patients to achieve improved uncorrected and spectacle-corrected vision. Outside the United States, some surgeons have performed topography-guided partial transepithelial photorefractive keratectomy (PRK) and collagen cross linking to treat post-LASIK corneal ectasia. Patient selection is very important, given the tissue removal at the time of cross linking. An alternative approach is delaying the consideration of excimer laser surface ablation until several months after cross linking is performed. Within the United States, keratoconus, forme fruste keratoconus, or other corneal ectasias are typically considered contraindications to excimer laser ablation.
The American Academy of Ophthalmology (AAO) Preferred Practice Pattern for Refractive Errors & Refractive Surgery lists the following conditions as contraindications for refractive surgery :
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Unstable refraction
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Active or recently active uveitis or uveitis that requires ongoing treatment or is recurrent in nature
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Corneal endothelial disease including Fuchs dystrophy
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Visually significant cataract in the case of phakic intraocular lenses (IOLs)
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Shallow anterior chamber in the case of phakic IOLs
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Uncontrolled autoimmune or other immune-mediated disease
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Uncontrolled glaucoma
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Uncontrolled external disease
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Unrealistic patient expectations
Ocular Hypertension and Glaucoma
Between 9% and 28% of myopic patients have primary open-angle glaucoma (POAG). The frequency of myopia in the glaucomatous population ranges from 6.6% to 37.8%, compared to 3% to 25% in the normal population. The risk of glaucoma development in low myopia (≤3.00 diopters [D]) is 1.65, whereas it is 2.46 for moderate to high myopia (>3.00 D) based on the pooled odds ratio of 48,161 individuals. Worldwide, the number of people with glaucoma in the population aged 40 to 80 years was estimated to be 64.3 million in 2012, and the number is estimated to increase to 76.0 million in 2020 and 111.8 million in 2040. The ophthalmic surgeon will encounter glaucoma in some candidates for prospective refractive surgery.
Of particular concern in the patient with ocular hypertension (OHT) or POAG undergoing LASIK is the effect of an acute intraocular pressure (IOP) rise to greater than 65 mm Hg when suction is applied during flap creation. Although the normal optic nerve seems to tolerate this IOP elevation, we do not yet fully know the resultant effect on the compromised optic nerve. There have been few reports of new visual field defects immediately after LASIK that have been attributed to mechanical compression or ischemia of the optic nerve head from the increase of IOP.
Evaluation of the patient with OHT or POAG includes a complete history and ocular examination with peripheral visual field and corneal pachymetry. Ocular computed tomography (OCT) may also assist the assessment of optic nerve cupping. A history of poor IOP control, noncompliance with treatment, maximal medical therapy, or prior surgical interventions may suggest progressive disease, which may contraindicate refractive surgery. As part of the complete dilated examination, the surgeon should note the status of the angle, presence and amount of optic nerve cupping, and degree of visual field loss.
Central corneal thickness must be considered in the evaluation of applanation IOP. The principle of applanation tonometry assumes a corneal thickness of 0.52 mm. The IOP is underestimated by 5.2 mm in corneas of 0.45-mm thickness. Corneal curvature can also influence IOP readings with an estimated 1 mm Hg of IOP increase for every 3-D increase in corneal curvature.
Many articles document the inaccuracy of IOP measurements after PRK or LASIK because of apparent lowering of the reading. These inaccurately low central applanation tonometry measurements have been reported to obscure the diagnosis of steroid-induced glaucoma after PRK or LASIK, resulting in optic nerve cupping, visual field loss, and decreased visual acuity ( Fig. 11.1 ). Because of the difficulty of interpreting IOP measurements after PRK or LASIK, these procedures should not be considered when the IOP is poorly controlled. Glaucoma referral should be obtained when indicated.
Patients with OHT can often have refractive surgery. They must be counseled preoperatively that the LASIK treats only the refractive error and not the natural history of the OHT, which can sometimes progress to glaucoma with optic nerve cupping and visual field loss. Particular attention should be paid to risk factors for progression to glaucoma including age, corneal thickness, cup/disc ratio, and IOP. Patients should also understand that refractive surgery will make it more difficult to accurately assess their IOP after excimer laser ablation. The refractive surgeon may want the patient to sign ancillary consent documenting their understanding that POAG may result in progressive visual loss independent of any refractive surgery.
Whether to perform refractive surgery in the patient with glaucoma is a controversial issue. LASIK is contraindicated in any patient with marked optic nerve cupping, visual field loss, or loss of visual acuity. Although most studies have not found a change in the optic disc or nerve fiber layer thickness after LASIK, there are no long-term studies on refractive surgery in the glaucoma population. A series of patients with pigment dispersion syndrome and glaucoma who are using an IOP-lowering agent concluded that they may have slower healing with decreased predictability of their visual outcome.
The surgeon should be aware that placement of a suction ring may not be possible if there is a functioning filtering bleb. Typically the glaucoma should be well controlled before refractive surgery is even considered. In the rare case where filtering surgery and LASIK are planned, it is preferable to perform the LASIK before the filter. Suction time should be minimized to decrease the chance of optic nerve damage from the transient increase of IOP. Alternatively, surface ablation might be preferable because it eliminates the IOP rise associated with use of the microkeratome. The surgeon must be careful with the use of postoperative steroids because of the potential elevation of IOP that may result. Postoperatively, the patient should be informed when to resume postoperative topical medications for glaucoma.
To avoid trauma to the flap, the IOP should not be checked for at least 72 hours. Both the ophthalmologist and the glaucoma patient must be aware that refractive surgery may change interpretation of diagnostic tests. Patients should be told that they must inform subsequent ophthalmologists of a prior excimer laser vision correction procedure as well as of the preoperative refractive error in order to assess the postoperative IOP more accurately. LASIK can also affect measurements of the thickness of the nerve fiber layer performed by scanning laser polarimetry because of the change in the corneal architecture.
Connective Tissue Disease
Most surgeons consider active uncontrolled connective tissue diseases―such as systemic lupus erythematosus and polyarteritis nodosa―to be contraindications to surface laser ablation because of reports of postoperative corneal melt and perforation. Late corneal scarring has been reported after PRK in a patient with systemic lupus erythematosus. Peripheral keratitis with infiltrates was reported to occur after LASIK in a patient with rheumatoid arthritis.
Corneal Dystrophies
Granular corneal dystrophy 2 (Avellino dystrophy) is an absolute contraindication to the performance of LASIK. LASIK and PRK result in marked progression of the dystrophy because of rapid accumulation of the Transforming growth factor-beta-induced protein (TGFBIp), which leads to a visual decrease. LASIK should also be avoided in Fuchs dystrophy.
Patient Expectations
The patient with unrealistic expectations is at high risk for being unhappy with the most successful result of refractive surgery. Consequently a patient with unrealistic expectations should be considered an absolute contraindication to performing the procedure.
Relative Contraindications
Patients with glaucoma should be treated with caution, especially if postoperative corticosteroid use may exacerbate IOP problems. Patients with incipient cataracts should also be avoided because refractive errors can be corrected during subsequent cataract surgery. Monocularity is a potential contraindication for refractive surgery. Surgery in an amblyopic eye may be undertaken in selected cases. Finally, prospective patients between the ages of 18 and 21 years should be considered only if their refraction is stable.
Immunodeficiency of any cause is a relative contraindication to refractive surgical procedures on the basis both of possible aberrant wound healing and of predisposition to infection in such patients. One might be less likely to perform PRK on a diabetic patient, for instance, for fear of a persistent epithelial defect following surgery. Preexisting corneal disease may lead to advice against any form of refractive surgery. Patients with a history of herpetic keratitis, for example, may be at risk for recrudescence of the disease following excimer laser surgery. Some studies have reported good results after LASIK in patients with well-controlled collagen vascular disease. Alio et al. reported the results of LASIK in 42 eyes of 22 patients with controlled autoimmune disease including rheumatoid arthritis, systemic lupus erythematosus, dermatomyositis, scleroderma, ankylosing spondylitis, psoriatic arthritis, inflammatory bowel disease, arthritis, and Behçet disease. There were no reports of corneal haze, melting, flap, or interface complications. These findings were confirmed by Schallhorn et al. in their retrospective review of 622 patients with well-controlled collagen vascular and other immune-mediated inflammatory disease. The postoperative complications were those expected after laser surgery with the exception of one peripheral flap melt that did respond to topical steroid treatment. The authors concluded that “Excimer laser surgery can be safely performed in patients with well-controlled collagen vascular or other immune-mediated inflammatory diseases.” However, performing LASIK in patients with these diseases, even when inactive, may still be controversial, as necrotizing keratitis after LASIK has been reported in patients with inactive colitis.
The response of patients with some of the corneal dystrophies, degenerations, and dysgeneses remains unclear; for example, patients with epithelial basement membrane degeneration have been reported to achieve safe, effective outcomes after surface laser ablation, avoiding the risk for significant epithelial abrasion during LASIK.
The potential for dry eye after corneal excimer laser surgery, though recognized, might be underestimated. Albeitz and colleagues reported that 38% of 450 consecutive patients undergoing LASIK for myopia exhibited dry-eye symptoms. Patients with dry-eye problems require careful evaluation. A patient with a mildly dry eye may be intolerant of contact lens wear and may reasonably be considered for a refractive procedure, although the added risk should be considered in deciding to perform such a procedure rather than correcting with spectacles. More significant problems with dry eyes require even more careful patient selection. Tsubota and colleagues have shown that patients with poor basal tear production but preserved reflex tearing can heal adequately after refractive surgery, achieving satisfactory outcomes. The decision to perform LASIK or laser-assisted subepithelial keratectomy (LASEK) on such dry-eye patients should take place on a per patient basis; it is helpful to ask the patient what he or she would consider a tolerable use of topical lubricant eye drops in the postoperative period. Use of topical agents such as cyclosporine or even topical autologous serum have both been shown to improve the ocular surface in dry eye and might be used in the postoperative period in extreme circumstances. Not all patients will elect to proceed with surgery if they are apprised of the likely burden of frequent topical medications in the postoperative period. More generally, it has been suggested that dry-eye problems after LASIK can affect the refractive accuracy of the procedure; however, prospective data from Toda and colleagues showed that there were no significant differences in procedure efficacy among those with dry eye, borderline dry eye, and those with normal tear function.
The AAO Preferred Practice Pattern for Refractive Errors & Refractive Surgery lists the following conditions as contraindications for refractive surgery :
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Significant eyelid, tear film, or ocular surface abnormalities related to keratoconjunctivitis sicca, blepharoconjunctivitis, acne rosacea, conjunctival cicatrization, corneal exposure, neurotrophic keratitis, or other corneal abnormalities
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History of uveitis
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Inflammation of the anterior segment
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Functional monocularity
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Presence of a filtering bleb
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Pseudoexfoliation
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Diabetes mellitus
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Autoimmune or other immune-mediated disease
Dry Eye
Many patients seek refractive surgery because underlying dry eye has resulted in contact lens intolerance. Any refractive surgery candidate with signs or symptoms of dry eyes should be thoroughly evaluated. Patient history should include questions about connective tissue diseases and conjunctival cicatrizing disorders, as these are relative contraindications to any refractive procedure and would have to be addressed prior to any surgical consideration. Patients are often satisfied by the outcomes of a LASIK procedure, but side effects such as dryness, burning, and discomfort are reported, which can range in severity and may significantly affect quality of life. LASIK is considered to lead to corneal nerve damage of the subbasilar plexus, which is permanent, and may cause some changes in the mechanism of corneal neurotransmission postsurgery.
External examination should include evaluation of the blink for such conditions as incomplete blink or lagophthalmos. On slit-lamp examination, the quantity and quality of the tear film are assessed, as is the presence of blepharitis, meibomitis, or keratitis. Ancillary testing for dry eyes―such as Schirmer testing and tear breakup time―can be performed.
If connective tissue diseases or cicatrizing diseases are suspected, appropriate referral or laboratory testing should be performed to rule out these conditions prior to consideration of refractive surgery. Preexisting abnormalities should be treated. Topical tear replacement and/or punctal occlusion can be performed. In appropriate cases, a preoperative course of topical anti-inflammatories such as topical steroid or cyclosporine may be indicated. Blepharitis and/or meibomitis should be treated. Adverse outcomes from refractive surgery can be minimized with proper management of the ocular surface before, during, and after LASIK.
A normal tear film layer is important for wound healing of the corneal stroma and epithelium. Epidermal growth factor, vitamin A, and IgA in the tears help to prevent postoperative infection and potentiate wound healing. Consequently severe dry eye has previously been thought to be a relative contraindication to refractive surgery.
In addition, LASIK may result in a temporary dry eye postoperatively because corneal nerves are severed when the flap is made. Proper management of the ocular surface through topical tear replacement therapy and/or punctal occlusion must be provided in the perioperative period.
Diabetes Mellitus
Diabetes mellitus affects 4% to 8% of Americans. Diabetic patients considering refractive surgery should undergo a thorough preoperative history and examination. The diabetes must be under good control to ensure an accurate refraction. A history of laser treatment for proliferative diabetic retinopathy or cystoid macular edema suggests visually significant diabetic complications that typically contraindicate refractive surgery. Any patient who has preexisting visually significant diabetic ocular complications is not a good candidate for refractive surgery. Such a patient’s ocular examination should include examination of the corneal epithelium to detect the health of the ocular surface and evaluate cataract formation and should also undergo a detailed retinal examination.
There are few long-term studies of refractive surgery in the diabetic patient. A retrospective review of 30 eyes from diabetic patients who had LASIK 6 months earlier revealed a complication rate of 47% compared with a control population’s complication rate of 6.9%. The most common problems were related to epithelial healing and included epithelial defects and erosions. Although the uncorrected visual acuity (UCVA) was worse in the diabetic group than in the controls, this was not statistically significant. There was a loss of two or more lines of best-corrected visual acuity (BCVA) in less than 1% in both the diabetic and the control groups. However, six diabetic eyes (6/30) required a mean time of 4.3 months to heal because of persistent epithelial defects. The authors concluded that the high complication rate in diabetic patients was explained by the unmasking of subclinical diabetic keratopathy. Another report described the progression and worsening of diabetic retinopathy occurring after LASIK.
The refractive surgeon should exercise caution in the selection of diabetic patients for refractive surgery. Intraoperative technique should be adjusted to ensure maximal epithelial health. In order to minimize corneal toxicity, the surgeon should use the minimal amount of topical anesthetic immediately before the procedure. Tears, not anesthetics, are used during the microkeratome pass.
Diabetic patients should be counseled preoperatively that there is an increased risk of postoperative complications and there may be prolonged healing time after LASIK. It has been well established that there is an increased association between surgical site infection and diabetes. In addition, such patients should understand that the procedure treats only the refractive error and not the natural history of the diabetes, which could lead to future diabetic ocular complications and associated visual loss. However, overall, if glycemic control is tight, with no presence of other ocular or systemic complications, LASIK in diabetic patients can be considered to be safe.
Human Immunodeficiency Virus
Little has been written on the performance of refractive surgery in patients with known HIV infection. Some surgeons counsel these patients against refractive surgery because of concerns for postoperative complications, including increased risk for infection associated with their immunosuppression. If the patient has progressed to AIDS, the underlying severe immunosuppression must be the paramount consideration. More importantly, these patients should be monitored for vision-threatening diseases such as cytomegalovirus retinitis. Most ophthalmologists consider AIDS to be an absolute contraindication to refractive surgery. The US Food and Drug Administration (FDA) lists immunodeficiency in patients as absolute contraindications to all excimer laser devices and warns patients that certain conditions such as HIV may prevent proper closure of the wound during wound healing. The AAO Preferred Practice Pattern for Refractive Management & Intervention also lists autoimmune or other immune-related disease as relative contraindications, and uncontrolled autoimmune or immune-related disease as absolute contraindications.
Because HIV-infected patients now live productive lives for longer periods before the onset of AIDS, the question of the appropriateness of refractive surgery in this “healthier” population will be asked more often. Uniform precautions must always be applied because the refractive surgeon may operate on patients who do not know they have been infected with viruses such as HIV or hepatitis. One concern is the vaporization of corneal tissue and potential for aerosolizing live virus during laser ablation, which could pose a risk to laser suite personnel.
In one study, excimer ablation of pseudorabies virus, a porcine enveloped herpes virus similar to HIV and HSV, did not appear capable of causing infection by transmission through the air.
The authors concluded that excimer laser ablation of the cornea in a patient infected with HIV is unlikely to pose a health hazard to the surgeon. In another study, after excimer laser ablation of infected corneal stroma, polymerase chain reaction (PCR) did not detect viable varicella virus (200 nm) but did detect viable polio particles (70 nm).
Although inhaled particles greater or equal to 5 µm are deposited in the bronchial, tracheal, nasopharyngeal, or nasal walls, those smaller than 2 µm are deposited in the bronchioles and alveoli. Even if viral particles are not viable, the excimer laser plume produces particles of a mean diameter of 0.22 µm, which can be inhaled. The health effects of inhaled particles from the plume have not yet been determined. There are anecdotal reports of respiratory ailments, such as chronic bronchitis, in laser surgeons. Canister filter masks can filter particles down to 0.1 µm and may be more protective than conventional surgical masks. In addition, evacuation of the laser plume may potentially decrease the amount of breathable debris.
Because of the many remaining questions, some surgeons consider patients with known HIV to be poor candidates for refractive surgery. In a 2010 survey study evaluating the preferences of 1123 surgeons in performing elective refractive surgery with patients with HIV positivity or AIDS, 25.4% responded, and about half of those who responded (50.2%) said that they considered HIV-positive persons acceptable candidates for refractive surgery, whereas only 12.5% said that they considered AIDS patients acceptable candidates. If a surgeon considers performing excimer laser ablation in the “healthy” HIV-infected patient with normal eye examination and excellent best-corrected vision, extra precautions should be taken. Among surgeons who said that they performed elective surgery in patients with AIDS or HIV positivity, 72.7% added that they take extra precautions when performing such surgery. The patient should be extensively counseled preoperatively concerning the visual risks of HIV and the lack of long-term follow-up of refractive surgery in this population. The surgeon should consider additional precautions such as wearing a filter mask during the procedure, evacuation of the laser plume, wearing a double layer of gloves, performing unilateral surgery, and scheduling the patient last on any given surgery day.
Previous Ocular Surgery
After Retinal Detachment Surgery
Retinal detachment surgery can result in myopic shift because of axial elongation of the eye from indentation of the scleral buckle. Refractive surgery can be considered when there is anisometropia with good BCVA. Although a study reported LASIK to be safe in eyes after retinal detachment surgery, the risk of vision regression is always higher in such eyes compared with eyes with no such previous surgery.
The retina should be extensively evaluated preoperatively. Referral to a retinal specialist should be made when indicated. The surgeon should determine whether conjunctival scarring or the scleral buckle will interfere with placement of the suction ring during the microkeratome pass. If so, PRK may be considered.
The patient must be informed that the role of the surgery is solely to treat the refractive error to correct anisometropia or to decrease dependency on corrective eye wear. Preoperative pathology including preexisting macular pathology will continue to limit their UCVA and BCVA after refractive surgery. Successful LASIK after retinal detachment surgery has been reported ( Fig. 11.2 ). In one series, 10 eyes of 9 patients who had LASIK for myopia after prior retinal detachment surgery were followed for 6 months. LASIK was successfully completed in eight eyes but aborted intraoperatively in two eyes because scarred conjunctiva prevented adequate suction. No eyes had retinal complications and all eyes had improvement in UCVA with no loss of BCVA.
Patients who have had prior retinal detachment surgery may have less predictable results after LASIK. Unexpected corneal steepening has been reported in patients undergoing LASIK with previously placed scleral buckles.
After Cataract Surgery
Cataract surgery requires careful preoperative measurements in order to ensure the accuracy of the IOL calculation. Nevertheless, unintentional clinically significant ametropia in the form of myopia, hyperopia, and/or astigmatism may occur after cataract surgery. A retrospective review of 11 consecutive cases of pseudophakic ametropia reported that 45% were due to error in axial length determination and 55% to surgeon or surgical team error. Refractive error after cataract surgery may result from preexisting astigmatism that was not addressed by implantation of an IOL to correct spherical refractive error. Sometimes removal of the natural lens can unmask corneal astigmatism that was previously balanced by the lenticular astigmatism. In addition, inaccuracies in IOL calculations may result in unexpected postoperative refractive errors. Finally, in some cases, the surgeon may plan a two-staged procedure called bioptics, with initial cataract surgery and IOL implantation followed by LASIK.
LASIK can be considered after there has been sufficient wound healing of the cataract surgery incision to avoid wound rupture ( Fig. 11.3 ). One study examined 22 eyes of 22 patients who underwent LASIK for the correction of residual myopia at least 1 year after the prior cataract surgery and IOL. At 12 months after LASIK, the spherical equivalent refraction was within ±1.00 D of emmetropia in 18 eyes (81.8%) and within ±0.50 D in 11 eyes (50%). No patients had any wound complications. Another study examined 20 eyes of 20 patients with refractive myopic or mixed astigmatism from 3.00 to 6.00 D following cataract extraction with IOL. LASIK was performed at least 3 months after prior surgery. At 6 months after LASIK, mean refractive cylinder decreased from 4.64 ± 0.63 D to 0.44 ± 0.24 D ( P < .001) and mean spherical equivalent refraction decreased from −2.19 ± 0.88 D (range −1.00 to −3.88 D) to −0.32 ± 0.34 D (range −1.25 to +0.38 D). No IOL or cataract incisions were related complications and no eyes lost any lines of BCVA.
PRK may be advantageous because it eliminates the IOP rise and wound stress associated with the use of the suction ring during the microkeratome pass. Consequently PRK does not stress the cataract surgery wound. A study carried out in 1999 examined 30 consecutive eyes of 30 patients who had PRK for residual myopia at least 6 months after cataract surgery. Although no patient had UCVA of 20/40 prior to LASIK, 53% achieved UCVA of 20/40 or better after LASIK. At 12 months, the spherical equivalent was within ±1.00 D of emmetropia in 27 eyes (90.0%) with no vision-threatening complications. Another study of 31 eyes in 24 patients demonstrated a decrease in anisometropia from 3.44 ± 1.07 D to 0.58 ± 0.31 D after PRK ( P < .01). There were no serious complications during or after the surgery.
Phakic IOL implantation for anisometropia from myopic astigmatism resulting after cataract extraction and IOL has been reported in 2 patients. One patient had UCVA of 20/400, which improved to 20/30 after phakic IOL, and the preoperative UCVA of another patient improved from 20/200 to 20/40 postoperatively. Neither patient had any complications.
Bioptics is a term coined by Zaldivar in the late 1990s to describe the combination of two or more refractive procedures. For example, LASIK can be performed after clear or cataract lens extraction with IOL implantation. The results of LASIK performed 1 month or more after lens extraction with IOL implantation were reported in 64 eyes of 55 patients. Preoperative mean spherical equivalent refraction was −2.61 and improved to +0.09 1 month after LASIK. Keratitis sicca occurred in 10%.
After Penetrating Keratoplasty
Despite successful Penetrating Keratoplasty (PKP), patients may have poor vision because of the high residual refractive error. Anisometropia may result if there is a large change in corneal curvature. High astigmatism may be difficult to correct adequately with spectacles. Irregular astigmatism can only be corrected with gas-permeable contact lenses. Ten percent to 30% of patients require contact lens correction after penetrating keratoplasty. However, contact lens fitting may not be possible because of the abnormal corneal curvature.
Refractive surgery can be performed to reduce refractive error after PKP in those patients who cannot tolerate contact lenses ( Fig. 11.4 ). Often the attainment of excellent postoperative UCVA is not a realistic goal. Depending on the original refractive error, refractive surgery may allow the patient to be fitted with a contact lens or may permit the use of spectacles (see Chapter 42 ).
Absolute Contraindications
Although advice regarding the propriety of refractive surgery must always be individualized to each patient’s risk-benefit ratio, the following situations include those in which refractive surgery is best avoided. Patients with poorly controlled systemic immunologic disorders such as rheumatoid arthritis, systemic lupus erythematosus, polyarteritis nodosa, and other collagen vascular diseases are at risk of inflammatory and wound-healing sequelae that may cause severe corneal complications. Refractive surgery in such patients is not advised. Contraindications may also derive from the health of the eye itself. Patients with severe dry eye syndromes―including those with conjunctival cicatrizing disorders like Stevens-Johnson syndrome, ocular cicatricial pemphigoid, and a chemically burned ocular surface―are poor candidates because of wound-healing problems that may supervene following surgery.
Patients with keratoconus and other ectatic corneal dystrophies should be identified preoperatively. Such patients may frequently present to the refractive surgical practice because of their poor vision with optical correction. Because the optical and physical effects of refractive procedures and the long-term prognoses are unclear in these patients, most refractive surgery is contraindicated in such situations. One exception to this rule might be consideration of insertion of intracorneal ring segments in patients with keratoconus who suffer contact lens intolerance or where a corneal transplant is inevitable; intracorneal ring segments in this situation have delayed but not prevented progression to corneal transplant. Patients with irregular astigmatism in the absence of keratoconus or ectasia should be managed with caution. The advent of wavefront sensors and the ability to custom reshape the cornea with the excimer laser has allowed some of these patients to achieve improved uncorrected and spectacle-corrected vision. Outside the United States, some surgeons have performed topography-guided partial transepithelial photorefractive keratectomy (PRK) and collagen cross linking to treat post-LASIK corneal ectasia. Patient selection is very important, given the tissue removal at the time of cross linking. An alternative approach is delaying the consideration of excimer laser surface ablation until several months after cross linking is performed. Within the United States, keratoconus, forme fruste keratoconus, or other corneal ectasias are typically considered contraindications to excimer laser ablation.
The American Academy of Ophthalmology (AAO) Preferred Practice Pattern for Refractive Errors & Refractive Surgery lists the following conditions as contraindications for refractive surgery :
- •
Unstable refraction
- •
Active or recently active uveitis or uveitis that requires ongoing treatment or is recurrent in nature
- •
Corneal endothelial disease including Fuchs dystrophy
- •
Visually significant cataract in the case of phakic intraocular lenses (IOLs)
- •
Shallow anterior chamber in the case of phakic IOLs
- •
Uncontrolled autoimmune or other immune-mediated disease
- •
Uncontrolled glaucoma
- •
Uncontrolled external disease
- •
Unrealistic patient expectations
Ocular Hypertension and Glaucoma
Between 9% and 28% of myopic patients have primary open-angle glaucoma (POAG). The frequency of myopia in the glaucomatous population ranges from 6.6% to 37.8%, compared to 3% to 25% in the normal population. The risk of glaucoma development in low myopia (≤3.00 diopters [D]) is 1.65, whereas it is 2.46 for moderate to high myopia (>3.00 D) based on the pooled odds ratio of 48,161 individuals. Worldwide, the number of people with glaucoma in the population aged 40 to 80 years was estimated to be 64.3 million in 2012, and the number is estimated to increase to 76.0 million in 2020 and 111.8 million in 2040. The ophthalmic surgeon will encounter glaucoma in some candidates for prospective refractive surgery.
Of particular concern in the patient with ocular hypertension (OHT) or POAG undergoing LASIK is the effect of an acute intraocular pressure (IOP) rise to greater than 65 mm Hg when suction is applied during flap creation. Although the normal optic nerve seems to tolerate this IOP elevation, we do not yet fully know the resultant effect on the compromised optic nerve. There have been few reports of new visual field defects immediately after LASIK that have been attributed to mechanical compression or ischemia of the optic nerve head from the increase of IOP.
Evaluation of the patient with OHT or POAG includes a complete history and ocular examination with peripheral visual field and corneal pachymetry. Ocular computed tomography (OCT) may also assist the assessment of optic nerve cupping. A history of poor IOP control, noncompliance with treatment, maximal medical therapy, or prior surgical interventions may suggest progressive disease, which may contraindicate refractive surgery. As part of the complete dilated examination, the surgeon should note the status of the angle, presence and amount of optic nerve cupping, and degree of visual field loss.
Central corneal thickness must be considered in the evaluation of applanation IOP. The principle of applanation tonometry assumes a corneal thickness of 0.52 mm. The IOP is underestimated by 5.2 mm in corneas of 0.45-mm thickness. Corneal curvature can also influence IOP readings with an estimated 1 mm Hg of IOP increase for every 3-D increase in corneal curvature.
Many articles document the inaccuracy of IOP measurements after PRK or LASIK because of apparent lowering of the reading. These inaccurately low central applanation tonometry measurements have been reported to obscure the diagnosis of steroid-induced glaucoma after PRK or LASIK, resulting in optic nerve cupping, visual field loss, and decreased visual acuity ( Fig. 11.1 ). Because of the difficulty of interpreting IOP measurements after PRK or LASIK, these procedures should not be considered when the IOP is poorly controlled. Glaucoma referral should be obtained when indicated.
Patients with OHT can often have refractive surgery. They must be counseled preoperatively that the LASIK treats only the refractive error and not the natural history of the OHT, which can sometimes progress to glaucoma with optic nerve cupping and visual field loss. Particular attention should be paid to risk factors for progression to glaucoma including age, corneal thickness, cup/disc ratio, and IOP. Patients should also understand that refractive surgery will make it more difficult to accurately assess their IOP after excimer laser ablation. The refractive surgeon may want the patient to sign ancillary consent documenting their understanding that POAG may result in progressive visual loss independent of any refractive surgery.
Whether to perform refractive surgery in the patient with glaucoma is a controversial issue. LASIK is contraindicated in any patient with marked optic nerve cupping, visual field loss, or loss of visual acuity. Although most studies have not found a change in the optic disc or nerve fiber layer thickness after LASIK, there are no long-term studies on refractive surgery in the glaucoma population. A series of patients with pigment dispersion syndrome and glaucoma who are using an IOP-lowering agent concluded that they may have slower healing with decreased predictability of their visual outcome.
The surgeon should be aware that placement of a suction ring may not be possible if there is a functioning filtering bleb. Typically the glaucoma should be well controlled before refractive surgery is even considered. In the rare case where filtering surgery and LASIK are planned, it is preferable to perform the LASIK before the filter. Suction time should be minimized to decrease the chance of optic nerve damage from the transient increase of IOP. Alternatively, surface ablation might be preferable because it eliminates the IOP rise associated with use of the microkeratome. The surgeon must be careful with the use of postoperative steroids because of the potential elevation of IOP that may result. Postoperatively, the patient should be informed when to resume postoperative topical medications for glaucoma.
To avoid trauma to the flap, the IOP should not be checked for at least 72 hours. Both the ophthalmologist and the glaucoma patient must be aware that refractive surgery may change interpretation of diagnostic tests. Patients should be told that they must inform subsequent ophthalmologists of a prior excimer laser vision correction procedure as well as of the preoperative refractive error in order to assess the postoperative IOP more accurately. LASIK can also affect measurements of the thickness of the nerve fiber layer performed by scanning laser polarimetry because of the change in the corneal architecture.
Connective Tissue Disease
Most surgeons consider active uncontrolled connective tissue diseases―such as systemic lupus erythematosus and polyarteritis nodosa―to be contraindications to surface laser ablation because of reports of postoperative corneal melt and perforation. Late corneal scarring has been reported after PRK in a patient with systemic lupus erythematosus. Peripheral keratitis with infiltrates was reported to occur after LASIK in a patient with rheumatoid arthritis.
Corneal Dystrophies
Granular corneal dystrophy 2 (Avellino dystrophy) is an absolute contraindication to the performance of LASIK. LASIK and PRK result in marked progression of the dystrophy because of rapid accumulation of the Transforming growth factor-beta-induced protein (TGFBIp), which leads to a visual decrease. LASIK should also be avoided in Fuchs dystrophy.
Patient Expectations
The patient with unrealistic expectations is at high risk for being unhappy with the most successful result of refractive surgery. Consequently a patient with unrealistic expectations should be considered an absolute contraindication to performing the procedure.
Ocular Hypertension and Glaucoma
Between 9% and 28% of myopic patients have primary open-angle glaucoma (POAG). The frequency of myopia in the glaucomatous population ranges from 6.6% to 37.8%, compared to 3% to 25% in the normal population. The risk of glaucoma development in low myopia (≤3.00 diopters [D]) is 1.65, whereas it is 2.46 for moderate to high myopia (>3.00 D) based on the pooled odds ratio of 48,161 individuals. Worldwide, the number of people with glaucoma in the population aged 40 to 80 years was estimated to be 64.3 million in 2012, and the number is estimated to increase to 76.0 million in 2020 and 111.8 million in 2040. The ophthalmic surgeon will encounter glaucoma in some candidates for prospective refractive surgery.
Of particular concern in the patient with ocular hypertension (OHT) or POAG undergoing LASIK is the effect of an acute intraocular pressure (IOP) rise to greater than 65 mm Hg when suction is applied during flap creation. Although the normal optic nerve seems to tolerate this IOP elevation, we do not yet fully know the resultant effect on the compromised optic nerve. There have been few reports of new visual field defects immediately after LASIK that have been attributed to mechanical compression or ischemia of the optic nerve head from the increase of IOP.
Evaluation of the patient with OHT or POAG includes a complete history and ocular examination with peripheral visual field and corneal pachymetry. Ocular computed tomography (OCT) may also assist the assessment of optic nerve cupping. A history of poor IOP control, noncompliance with treatment, maximal medical therapy, or prior surgical interventions may suggest progressive disease, which may contraindicate refractive surgery. As part of the complete dilated examination, the surgeon should note the status of the angle, presence and amount of optic nerve cupping, and degree of visual field loss.
Central corneal thickness must be considered in the evaluation of applanation IOP. The principle of applanation tonometry assumes a corneal thickness of 0.52 mm. The IOP is underestimated by 5.2 mm in corneas of 0.45-mm thickness. Corneal curvature can also influence IOP readings with an estimated 1 mm Hg of IOP increase for every 3-D increase in corneal curvature.
Many articles document the inaccuracy of IOP measurements after PRK or LASIK because of apparent lowering of the reading. These inaccurately low central applanation tonometry measurements have been reported to obscure the diagnosis of steroid-induced glaucoma after PRK or LASIK, resulting in optic nerve cupping, visual field loss, and decreased visual acuity ( Fig. 11.1 ). Because of the difficulty of interpreting IOP measurements after PRK or LASIK, these procedures should not be considered when the IOP is poorly controlled. Glaucoma referral should be obtained when indicated.
Patients with OHT can often have refractive surgery. They must be counseled preoperatively that the LASIK treats only the refractive error and not the natural history of the OHT, which can sometimes progress to glaucoma with optic nerve cupping and visual field loss. Particular attention should be paid to risk factors for progression to glaucoma including age, corneal thickness, cup/disc ratio, and IOP. Patients should also understand that refractive surgery will make it more difficult to accurately assess their IOP after excimer laser ablation. The refractive surgeon may want the patient to sign ancillary consent documenting their understanding that POAG may result in progressive visual loss independent of any refractive surgery.
Whether to perform refractive surgery in the patient with glaucoma is a controversial issue. LASIK is contraindicated in any patient with marked optic nerve cupping, visual field loss, or loss of visual acuity. Although most studies have not found a change in the optic disc or nerve fiber layer thickness after LASIK, there are no long-term studies on refractive surgery in the glaucoma population. A series of patients with pigment dispersion syndrome and glaucoma who are using an IOP-lowering agent concluded that they may have slower healing with decreased predictability of their visual outcome.
The surgeon should be aware that placement of a suction ring may not be possible if there is a functioning filtering bleb. Typically the glaucoma should be well controlled before refractive surgery is even considered. In the rare case where filtering surgery and LASIK are planned, it is preferable to perform the LASIK before the filter. Suction time should be minimized to decrease the chance of optic nerve damage from the transient increase of IOP. Alternatively, surface ablation might be preferable because it eliminates the IOP rise associated with use of the microkeratome. The surgeon must be careful with the use of postoperative steroids because of the potential elevation of IOP that may result. Postoperatively, the patient should be informed when to resume postoperative topical medications for glaucoma.
To avoid trauma to the flap, the IOP should not be checked for at least 72 hours. Both the ophthalmologist and the glaucoma patient must be aware that refractive surgery may change interpretation of diagnostic tests. Patients should be told that they must inform subsequent ophthalmologists of a prior excimer laser vision correction procedure as well as of the preoperative refractive error in order to assess the postoperative IOP more accurately. LASIK can also affect measurements of the thickness of the nerve fiber layer performed by scanning laser polarimetry because of the change in the corneal architecture.
Connective Tissue Disease
Most surgeons consider active uncontrolled connective tissue diseases―such as systemic lupus erythematosus and polyarteritis nodosa―to be contraindications to surface laser ablation because of reports of postoperative corneal melt and perforation. Late corneal scarring has been reported after PRK in a patient with systemic lupus erythematosus. Peripheral keratitis with infiltrates was reported to occur after LASIK in a patient with rheumatoid arthritis.
Corneal Dystrophies
Granular corneal dystrophy 2 (Avellino dystrophy) is an absolute contraindication to the performance of LASIK. LASIK and PRK result in marked progression of the dystrophy because of rapid accumulation of the Transforming growth factor-beta-induced protein (TGFBIp), which leads to a visual decrease. LASIK should also be avoided in Fuchs dystrophy.
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