Laser vision correction has benefited countless myopes by reducing their dependence on glasses and correspondingly enhancing their quality of life. However, with increasing degrees of laser vision correction available, the postoperative quality of vision may possibly decrease for reasons such as severe flattening of the corneal curvature as well as induced spherical aberration, especially at the junction of the treated and untreated corneal tissues. Therefore, highly myopic patients, whose quality of life is poorest due to their absolute dependence on thick spectacles or contact lenses, are often not ideal candidates for corneal refractive surgery. For these individuals, lens-based surgery in the form of phakic IOLs or refractive lens exchange may offer hope for visual improvement. These types of surgeries may also benefit moderately myopic patients with cataracts as well as treat presbyopia and effectively reduce higher-order aberrations with proper IOL choice.

CHOOSING THE BEST PROCEDURE

Despite lens-based surgery's potentially superior visual outcomes compared with corneal procedures, the surgeon must examine its risk-benefit ratio in order to validate the appropriateness of the approach. An examination of the Ophthalmic Mutual Insurance Company's consent forms for the two procedures reveals their striking similarity regarding such risks as infection, corneal edema/scarring (which could possibly require a penetrating keratoplasty), possible equipment malfunction, retinal detachment, hemorrhage, retinal vein or artery occlusion, blindness, and the loss of the eye.1 The two consent forms differ slightly in that LASIK's risks include an incorrect laser power setting and a patient's under- or overresponse. Refractive lens exchange includes the risk of a miscalculated IOL power, a poorly positioned IOL, and cystoid macular edema. Although the last is listed only with refractive lens exchange, its actual rate is extremely low.2

Although retinal detachment is a potential risk for both surgical modalities, a review of the literature reveals a potential disparity in relative risk, because there is considerable variability in findings regarding the incidence of retinal detachment in refractive lens exchange. Furthermore, the studies differ greatly with regard to their scopes, criteria, and follow-up durations. For example, Güell et al examined 44 eyes with a mean correction of -15.77D for 4 years and found a 0% retinal detachment rate.3 Fernandez-Vega et al examined 190 eyes with a 26- to 39-mm axial length for 5 years and found a 2.1% rate of retinal detachment.4 Pucci examined 25 eyes with corrections of greater than -12.00D for 43 months and found a 4% incidence of retinal detachment.5 Arne studied 36 eyes with -17.00D manifest refractions and 28-mm axial lengths for 4 years and found a 5.5% incidence of retinal detachment (in two eyes, both of which received PMMA IOLs and underwent a YAG posterior capsulotomy.6 Fritch examined 481 eyes with axial lengths greater than 26mm for 7 years and found only a 0.4% incidence of retinal detachment, one-tenth the rate of Pucci's study.7 The highest rate of retinal detachment (8.1%) was found by Colin et al,8 who examined 52 eyes that were treated for more than 12.00D of myopia for 7 years.

SANDERS' ANALYSIS

In order to sort through this somewhat perplexing range of outcomes from differently designed studies, Sanders performed an extensive review of 14 studies of retinal lens exchange with a PCIOL.2 These studies included a total of 1,372 myopic eyes (range, -6.00 to

-33.75D) of patients mostly in their 30s and 40s. All but 46 surgeries were performed with phacoemulsification, and the follow-up ranged from 15 to 45.9 months. Of all eyes, only 14 developed retinal detachments, an incidence of 1%. Sanders also examined the rate of cystoid macular edema in this review of the literature and found it to be only 0.1%. Although some of the studies were somewhat limited in their length of follow-up, Sanders' review is commendable for attempting to apply some homogeneity to this area of study.

Moreover, this review is significant for looking beyond the simple incidence of retinal detachment to the visual sequelae of this event. Sanders noted that retinal reattachment rates averaged 85%, with some series quoting success rates as high as 98%. However, the final BCVA after reattachment varied, with 60% of patients achieving 20/40 or better, 20% achieving 20/50 to 20/100, and 20% being worse than 20/100. By combining these visual outcomes data with the actual retinal detachment data from the 14 studies, Sanders determined an overall long-term incremental risk of moderate-to-severe vision loss with myopic refractive lens exchange of 4%.
Sanders' estimate was based on his compiled 1% incidence of retinal detachment with myopic refractive lens exchange. His estimate for visual loss would have been considerably worse had he used data from Colin et al, who showed an 8.1% rate of retinal detachment at 7 years.8 These data are disturbing for several reasons. For example, comparing them with the 4.8% incidence of retinal detachment predicted by Perkins9 at 7 years shows an incremental risk of this complication with refractive lens exchange of 3.3%. Moreover, the Colin study mirrored the Perkins study at 4 years with a 2% incidence (one eye in the Colin study). The three additional eyes with retinal detachment in the Colin study underwent a YAG posterior capsulotomy at 4 to 4.5 years postoperatively, and they all experienced retinal detachment within 2 years afterward. Arne's article also showed an association with YAG capsulotomy.6

MECHANISM OF RETINAL DETACHMENT WITH REFRACTIVE LENS EXCHANGE

The mechanism of YAG-induced retinal detachment is thought to be that the laser's energy and resultant shock waves destabilize the hyaluronic acid matrix that supports the vitreous-cortex structure and lead to an anomalous posterior vitreous detachment, which in turn produces a retinal detachment.10 Another theory predicts that the YAG energy disrupts the anterior hyaloid face, decreases the concentration of hyaluronic acid, and leads to an anomalous posterior vitreous detachment, which in turn leads to retinal detachment.11

Even without a YAG laser capsulotomy, cataract surgery alone can conceivably induce a retinal detachment. For example, the anterior shifting of the vitreous can produce peripheral and posterior retinal traction that leads to breaks. Although this anterior shifting is reduced by a properly placed PCIOL with posterior angulated haptics, it can still occur intraoperatively prior to the IOL's placement. Retinal traction may also occur as a result of the inertial destabilization of vitreous intraoperatively, although this retinal traction is also likely reduced by a properly placed PCIOL with posterior angulated haptics. Prior to such stabilization by the IOL, variable anterior chamber pressures and turbulence may proportionately and adversely mobilize the vitreous; therefore, attention to phacodynamic settings and proper instrument manipulation may be helpful in reducing the vitreous' movement.12 These vitreous dynamics could conceivable play a role in phakic IOL implantation in which anterior chamber pressures also vary with attendant changes in the anterior chamber's depth and potential retinal traction.

Additional considerations come into play when postulating the mechanism of retinal detachment in young myopes, in whom early vitreous liquefaction (synchesis) increases the chance for vitreous collapse (syneresis) and posterior vitreous detachment. The last produces an inertial destabilization of the vitreous that creates traction on the anteriorly attached retina, but these forces do not typically result in a retinal tear in a naturally occurring posterior vitreous detachment in an older patient due to the weaker vitreoretinal adhesions that produced this detachment initially. However, an anomalous posterior vitreous detachment occurs in young myopes prior to normal age-related vitreoretinal dehiscence; therefore, a break is more likely due to inertial vitreal traction's being more directly transmitted to the retina. Furthermore, the young myope will have synchesis as described earlier, which is more likely to dissect through a break as opposed to formed vitreous; this dissection typically results in retinal detachment.13

PRESENT AND FUTURE GUIDELINES

Given the potentially increased risk of retinal detachment in myopic refractive lens exchange, what should ophthalmologists do now and in the future? They should inform patients of the disparity in the literature. Some articles state an unchanged or even reduced risk of retinal detachment relative to a myope's natural history. They may also mention the most conservative estimates, with Sanders stating a 4% incremental risk of moderate-to-severe visual loss with retinal lens exchange and Colin et al suggesting a 3% incremental risk of retinal detachment. A retinal specialist should evaluate these patients preoperatively and consider retinal detachment prophylaxis such as laser or cryoretinopexy for suspicious areas. However, Goldberg found equivocal benefits of retinal detachment prophylaxis.14 He noted retinal breaks in or away from areas of prophylactic treatment. Inflammation from treatment could also induce other sequelae such as an epiretinal membrane, posterior vitreous detachment, or retinal detachment.

Moving into the future with myopic refractive lens exchange, a new, large database of age-matched controls must be established for the natural history of myopia for varying levels of axial length and ametropia to verify the baseline incidence of retinal detachment. The Perkins data9 are limited and 25 years old, and yet they form the benchmark for judging the incremental risk of retinal detachment. A large, prospective, multicenter study of refractive lens exchange should be organized with standardization of modern small-incision techniques and technology, notwithstanding the inevitable change in these factors with the rapid advances in this area of ophthalmology. The study should also span

10 or more years, given the late occurrences of retinal detachment in the Colin study. Also for the future, more studies are needed to validate the role of retinal detachment prophylaxis preoperatively given the doubts cast by Goldberg.14 Objective evaluative modalities of the vitreous should be developed as preoperative predictors of retinal detachment risk with myopic refractive lens exchange, such as dynamic light scattering or 3-D B-scan ultrasonography.14 Further evaluation is also needed on the potential role of pharmacologic vitreolysis for prophylaxis against retinal detachment in the face of anomalous posterior vitreous detachments.

In summation, the literature has indicated a potentially increased risk of retinal detachment14 with refractive lens exchange in myopia. With proper informed consent and meticulous attention to surgical technique (to minimize the disturbance of the vitreous and reduce the likelihood of posterior capsular opacification requiring YAG posterior capsulotomy), refractive lens exchange is a viable procedure that can significantly enhance the quality of life for these myopic patients. 

Barry S. Seibel, MD, is Clinical Assistant Professor of Ophthalmology at UCLA Medical School in Los Angeles and is in private practice in Beverly Hills, California. Dr. Seibel may be reached at (310) 273-0323; eyedoc2020b@earthlink.net.

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