To view Table 1 of this article please refer to the print version of our October issue, page 29.
LASIK has proven to be an effective procedure for correcting low-to-high myopia,1 but the patients whom LASIK benefits most are also those at the highest risk for developing rhegmatogenous retinal detachments (RRDs). The Eye Disease Case-Control Study Group2 showed that low myopes (eg, -1.00 to -3.00 D) have a fourfold increase in retinal detachment over nonmyopes. This risk increased tenfold when the patient's refractive error exceeded -3.00 D.
In 1998, a published case report3 described bilateral retinal detachments from giant retinal tears 2 months after LASIK on a highly myopic patient. The physicians suggested that either sudden changes in IOP that occurred during suction just prior to engaging the microkeratome or the shock wave generated by the excimer laser resulted in changes in the vitreous that may have led to the retinal detachments. Since the publication of that report, many ophthalmologists have suggested that all LASIK patients should undergo an extensive retinal evaluation with prophylactic photocoagulation of areas of lattice degeneration, atrophic holes, and/or flap tears prior to undergoing LASIK in an attempt to reduce any risk of a retinal detachment.1 Nevertheless, the literature is vague regarding whether any connection actually exists between LASIK surgery and RRDs.
REPORTED RISK RATES
Ophthalmologists have known for years that myopia is associated with an increased incidence of retinal detachments.2 In fact, the yearly incidence of a spontaneous RRD has been estimated at 0.015% in myopic eyes with up to -4.75 D of refractive error, 0.07% in eyes with ametropias of between -5.00 and -9.75 D, and 0.075% in eyes with greater than -10.00 D of refractive error.4 Furthermore, lifetime risks were 0.2% in hyperopes, emmetropes, and myopes with refractive errors of as great as -1.00 D, but the risk increased to 7% for eyes with greater than -9.00 D of refractive error.5
Several recent studies have attempted to evaluate the incidence of retinal detachment in post-LASIK patients. The largest study6 illustrated a 0.02% yearly incidence in patients who had an average refractive error of -6.00 D, a finding that indicates a lack of association between LASIK and RRD. Several smaller studies,1,7,8 however, reported a higher incidence of RRDs in patients who had undergone prior LASIK than would be predicted from myopia alone. Table 1 illustrates that these studies found a calculated yearly incidence of between 0.02% and 0.30%, but the comparisons that the investigators made were limited by subjects' different degrees of myopia, highly variable follow-up times, and the retrospective nature of most of the studies.1,6-8 No large, long-term, case-controlled, prospective study has ever been undertaken to properly evaluate the issue. As a result, debate continues as to whether LASIK increases patients' risk of experiencing an RRD.
IS THERE AN ASSOCIATION?Yes
Several ophthalmologists have published their ideas and observations in an effort to explain a possible relationship between LASIK and RRD. These individuals rely on the theory that “trauma” from various steps in the LASIK procedure contributes to an increased risk of RRD. Many post-LASIK RRD patients have some characteristics in common with patients who suffer traumatic retinal detachments: young age, giant retinal tears, and the relatively short time period between the “trauma” and RRD (less than 2 years).9 Additionally, the rapid suction (IOP of greater than 65 mm Hg) and/or excimer laser-induced shock waves (pressure as high as 100 atm) caused by the high number of energy pulses required to achieve adequate surgical results in moderate and high myopes could theoretically provide the “trauma” in question.6,7
Some investigators have suggested that a delayed posterior vitreous detachment (PVD) from premature vitreous liquefaction associated with myopia can account for the time delay between the LASIK procedure and the development of an RRD.7 In fact, one small prospective study found that one (2%) of 50 patients with refractive errors of less than -4.00 D and five (10%) of 50 patients with refractive errors of greater than -7.00 D developed a PVD shortly after undergoing LASIK.10 In another study, 78% of the retinal breaks occurred in the temporal quadrant, a finding that could be attributed to the additional pressure that the microkeratome applied on the temporal side of the eyes.6
No
By contrast, many ophthalmologists believe that the retinal detachments observed after LASIK are simply chance occurrences related more to the effects of myopia than LASIK. The time differential (average of 5 to14 months [Table 1]) between the LASIK procedure and incidence of RRD argues against any direct causation, although delayed PVD, as noted earlier, may be a mitigating factor. A large natural history study found that, for all cases in which retinal tears led to a detachment, the retinal detachment occurred within 6 weeks of the development of the retinal tears.11
Likewise, PVDs have been associated with an increased risk of RRD. Investigators found a prevalence of 12.5% (unrelated to LASIK) in highly myopic patients aged between 20 and 29 years.12 Furthermore, another study reported that 27% of pre-LASIK patients, averaging 33 years old, possessed a PVD.1 These studies highlight the relatively large PVD frequency in high myopes of younger ages. Any PVD and subsequent RRD in a post-LASIK patient, therefore, could simply be due to a spontaneous PVD that is unrelated to prior LASIK surgery.
In addition, one report highlighted how ocular pneumoplethysmography—the study of more than 69,000 tests of ocular blood flow using a device that applies suction to the globe to create IOPs in excess of 100 mm Hg—has never been shown to create a retinal detachment. Additional biomechanical studies on pneumoplethysmography patients have illustrated minimal eye-wall displacement and vitreous disturbance.13 Another investigator showed the simplicity of achieving an IOP as high as 70 mm Hg simply by vigorously squeezing the eyelids, a demonstration that makes the IOP achieved during LASIK appear somewhat unremarkable.14
THE ROLE OF PROPHYLACTIC PHOTOCOAGULATION
Is prophylactic photocoagulation of asymptomatic lattice degeneration, atrophic holes, and flap tears indicated prior to LASIK? One could argue that prophylactic peripheral retinal photocoagulation lessens the incidence of an RRD by closing any potential sources of subretinal fluid. Many experts recommend prophylactic photocoagulation and routinely have all their LASIK patients undergo a thorough retinal examination prior to the LASIK procedure.1,6 Interestingly, in the study with the lowest incidence of RRD, every patient underwent a thorough retinal evaluation and prophylactic photocoagulation treatment if needed prior to the LASIK procedure.6
Unfortunately, there have been no prospective studies directly comparing prophylactic treatment versus nontreatment and showing any definite RRD risk reduction for asymptomatic retinal lesions in general. Numerous physicians would argue that no compelling evidence exists to recommend prophylactic treatment. They assert that the risk of retinal detachment in eyes with significant myopia or lattice degeneration is not altered by prophylactic treatment, and, therefore, the procedure is not indicated because its long-term complications are unknown.15-17
Additionally, the premise of an association between LASIK and RRD hinges on the theory that LASIK induces some form of trauma, but eyes with lattice degeneration are not at an increased risk of RRD after a traumatic injury.5 Finally, one investigator16 highlighted the potential futility of vigorous prophylactic pretreatment and noted that between 25% and 72% of retinal detachments involved retinal tears in areas far removed from any previously known retinal pathology.
Whether a patient undergoes prophylactic photocoagulation or not, the studies described in this article have shown that an RRD is sometimes inevitable. Investigators have suggested that the vitreoretinal surgeon use cryopexy, argon laser retinopexy, pneumatic retinopexy, or vitrectomy without a scleral buckle to treat an RRD.6 The most appropriate form of treatment, however, often is a scleral buckle, which nullifies the refractive surgeon's prior work by inducing a myopic shift.1 The surgeon could later address this shift by means of a LASIK enhancement as long as the eye possesses sufficient corneal tissue.
CONCLUSION
Unfortunately, ophthalmologists have yet to reach a clear consensus regarding an association between LASIK and RRD. Until investigators undertake a large-scale prospective study, conclusions about whether such an association exists will continue to be speculative, and the use of prophylactic photocoagulation will remain physician-dependent. At the current time, it seems most prudent to have patients undergo a dilated fundus examination prior to LASIK; symptomatic breaks and all horseshoe tears should receive treatment, but the value of treating asymptomatic operculated or atrophic holes is unknown.
Thomas A. Ciulla, MD, performs clinical research and practices at the Retina Service of the Midwest Eye Institute in Indianapolis, Indiana. Dr. Ciulla may be reached at (317) 817-1822; thomasciulla@yahoo.com.
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