Cataract after Laser Iridotomy: Author Reply

Letters to the Editor Cataract after Laser Iridotomy Dear Editor: We read Lim et al’s article suggesting a possible association between prophylactic laser iridotomy and progression of lens opacity with considerable interest.1 The World Health Organization rates glaucoma as the second greatest cause of blindness worldwide2 and the leading cause of blindness that is not potentially reversible. Angle closure accounts for around half of all cases of primary glaucoma worldwide.3 Laser iridotomy increases angle width significantly in the majority of people with narrow angles and is effective in preventing angle closure in those who have suffered a symptomatic attack. We consider prevention of blindness from angle-closure glaucoma using biometric screening and prophylactic laser iridotomy to be a potentially viable public health strategy, especially in East Asia.4 Given the large numbers of people who would potentially benefit from prophylactic laser iridotomy and, therefore, be exposed to the procedure, any potential adverse sequelae of laser iridotomy must be taken seriously. The finding of an increased progression of cataract after iridotomy, if verified in further independent research, has important implications. However, we believe this study is inconclusive, as several potential sources of bias exist. Ninety subjects were recruited, but 5 underwent cataract surgery during the study, suggesting that they had significant cataract at enrollment. We are concerned that the 33% who were lost to follow-up may have differed from those who remained in the study. Specifically, we believe they were more likely to have had fewer symptoms, which could have been associated with less cataract development. As the authors note, visual acuity (VA) in those with progression of cataract decreased on average by 1 line. This potential bias affecting who remained in the study would have inflated the apparent size of any possible adverse effect. In addition, we believe that inadvertent observation bias may have influenced the findings. Although the 2 observers who performed the lens grading were masked to the results of previous examinations, they were aware that laser iridotomy had been performed and were not masked to the hypothesis being tested. Furthermore, an assessment of interobserver agreement was not performed. Consequently, measurement error remains a possibility. The proportions of people with progression in lens opacity in this study are 5%, nuclear sclerosis (95% confidence interval [CI], 1.7–13.7); 6.7%, cortical (95% CI, 2.6 –15.9); and 16.7%, posterior subcapsular (95% CI, 9.3–28.0). Lim et al cite figures of incident lens opacity from populationbased research. However, none of these studies are in Asian populations, and cataract progression rates may be higher in this group than in those from Barbados or Beaver Dam. Furthermore, the main finding of the study is progression of posterior subcapsular lens opacities, not incidence. Clinical experience supports the belief that established posterior subcapsular opacities often progress rapidly. We therefore feel that the failure to differentiate between incidence and

progression of posterior subcapsular opacities is an important limitation of this study. Finally, the reported results are not consistent with our experience in a study of 160 eyes of 98 Mongolian people treated in a community setting by laser iridotomy for narrow angles, angle closure, and angle-closure glaucoma.5 In 1998 (3 years after treatment in 1995), we found that Snellen VA had dropped by ⱖ2 lines in 8 of 62 (13%) people treated by laser iridotomy. However, in a group of untreated controls (deemed normal from the same population) VA had dropped by the same amount in 15 of 98 (15%; ␹2 ⫽ 3.3, P ⫽ 0.19). We believe that failure to recruit a control group is a significant limitation of the data reported by Lim et al. In conclusion, though their study raises concerns about the safety of laser iridotomy, potential biases and the lack of a proper control group make it impossible to conclude that iridotomy results in cataract progression. We are concerned that such a suggestion, without robust supportive evidence, may deter some ophthalmologists from using what appears to be a safe and largely effective method of preventing one of the world’s leading causes of blindness. JENNIFER L. Y. YIP, MRCOPHTH EMMA JONES, MRCOPHTH PAUL J. FOSTER, MD, PHD London, United Kingdom WINNIE P. NOLAN, DM, FRCOPHTH Singapore DAVID S. FRIEDMAN, MD, MPH Baltimore, Maryland References 1. Lim LS, Husain R, Gazzard G, et al. Cataract progression after prophylactic laser peripheral iridotomy. Potential implications for the prevention of glaucoma blindness. Ophthalmology 2005; 112:1355–9. 2. Resnikoff S, Pascolini D, Etya’ale D, et al. Global data on visual impairment in the year 2002. Bull World Health Organ 2004;82:844 –51. 3. Quigley HA. Number of people with glaucoma worldwide. Br J Ophthalmol 1996;80:389 –93. 4. Nolan WP, Baasanhu J, Undraa A, et al. Screening for primary angle closure in Mongolia: a randomised controlled trial to determine whether screening and prophylactic treatment will reduce the incidence of primary angle closure glaucoma in an East Asian population. Br J Ophthalmol 2003;87:271– 4. 5. Nolan WP, Foster PJ, Devereux JG, et al. YAG laser iridotomy treatment for primary angle closure in East Asian eyes. Br J Ophthalmol 2000;84:1255–9.

Author reply Dear Editor: We thank Yip et al for their interest in our article and acknowledge their recognition of the importance of potential adverse sequelae of laser peripheral iridotomy (LPI). We hope to clarify some of the points raised in their letter.

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Ophthalmology Volume 113, Number 8, August 2006 We agree with Yip et al that a number of our subjects were lost to follow-up and that this may affect the robustness of our results. Although it is a valid point that subjects lost to follow-up may have had fewer symptoms than those who remained in the study, logistic regression analysis of risk factors for cataract progression did not show an association between symptoms and progression of lens opacity. Yip et al also assumed that the existence of 5 subjects who underwent cataract extraction during follow-up implied a high rate of preexisting disease. The need for early cataract surgery might be attributed equally to even more rapid cataract progression than what was seen in the rest of the study population, and that these individuals might in fact reflect the more severe spectrum of LPI-induced lens opacity. We were interested particularly in the previous experience of the correspondents relating to Mongolian patients.1 The Mongolian study, which showed equal decrease in visual acuity (VA) after 3 years in both the control and study groups, however did not examine lens opacity; cataract progression was only inferred by their results of VA.1 The Mongolian subjects also underwent LPI with a neodymium:yttrium–aluminum– garnet laser alone, whereas subjects in our study underwent sequential LPI, with argon laser pretreatment, which may have different side effects. Differentiating between incidence and progression of cataract is a valid issue. The Lens Opacities Classification System III (LOCS III) is designed to provide semiobjective assessment of lens opacity, and comparisons between studies using this system often are performed. We employed a definition of progression and incidence very similar to that used in the Barbados Eye Study.2 In our article, incidence rates from our study were in fact calculated separately and presented distinct from progression rates, and this was mentioned in “Discussion.” Using a definition of cataract incidence as an increase in LOCS score by ⱖ2 units in eyes with baseline scores ⬍ 2 units, incidences of cataract in nuclear, cortical, and posterior subcapsular regions over 1 year calculated using this criterion in our study population were 0%, 8.2%, and 18.9%, respectively, demonstrating a marked preponderance of incidence of posterior subcapsular opacities. The corresponding rates in the Barbados Eye Study over 4 years were 9.2%, 22.2%, and 3.3% for nuclear, cortical, and posterior subcapsular opacities,2 whereas the figures from the Longitudinal Study of Cataract after 5 years of follow-up were 8%, 7.7%, and 4.3%, respectively.3,4 We found that an increased LOCS score for any or all regions at baseline was not a significant risk factor for incidence of lens opacity. As we pointed out in the original article, our observational study was indeed limited by the absence of a control group that did not undergo laser iridotomy. Although we are able confidently to give a progression rate for the treated eyes, we cannot compare this with the background rate. However, we believe that an increase of 2 LOCS III units in the posterior subcapsular region in 16.7% of our subjects within 1 year of laser iridotomy is a significant finding, despite the lack of a control group. Finally, we clarify that it was not our intention to discourage ophthalmologists from performing laser iridotomies. Rather, it was to report a potentially important com-

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plication of a procedure that warrants further study simply by virtue of the great frequency with which it is performed. If large-scale population-based screening and preventive measures for angle closure are to be introduced, it is essential that even an infrequent adverse event needs to be investigated. We hope that other groups may improve on our work by conducting a better controlled study. GUS GAZZARD, MD, FRCOPHTH LAURENCE S. LIM, MBBS RAHAT HUSAIN, MRCOPHTH STEVE K. L. SEAH, FRCS(ED), FRCOPHTH TIN AUNG, PHD, FRCS(ED) Singapore References 1. Nolan WP, Foster PJ, Devereux JG, et al. YAG laser iridotomy treatment for primary angle closure in East Asian eyes. Br J Ophthalmol 2000;84:1255–9. 2. Leske MC, Wu SY, Nemesure B, et al. Incidence and progression of lens opacities in the Barbados Eye Studies. Ophthalmology 2000;107:1267–73. 3. Leske MC, Chylack LT Jr, Wu SY, et al. Incidence and progression of nuclear opacities in the Longitudinal Study of Cataract. Ophthalmology 1996;103:705–12. 4. Leske MC, Chylack LT Jr, He Q, et al. Incidence and progression of cortical and posterior subcapsular opacities: the Longitudinal Study of Cataract. Ophthalmology 1997;104:1987–93.

Persistent Epithelial Ingrowth Dear Editor: Patients who have undergone radial keratotomy (RK) may experience a significant refractive shift over time1 and seek excimer laser surgical correction for their ametropia. When considering retreatment options after RK, there is debate about which technique is best, yielding the safest and most predictable outcomes with the most manageable potential complications. We report 3 patients who developed significant, persistent, recurrent epithelial ingrowth resulting from LASIK retreatment after RK, illustrating the potentially serious complication that can arise from this treatment. The first patient had 6-incision RK performed bilaterally in 1991, followed by LASIK in the left eye in March 1999, with enhancement in March 2002. Epithelial ingrowth occurred postoperatively, and a flap lift with epithelial debridement was performed in August 2002. In October 2002, uncorrected visual acuity (VA) was 20/200 in the left eye, and best spectacle-corrected VA (BSCVA) was 20/50 in the left eye, with a manifest refraction of ⫺2.50 ⫹3.75 ⫻75. Slit-lamp examination demonstrated extensive midperipheral epithelial ingrowth under the LASIK flap (Fig 1 [available at http://aaojournal.org]). The patient underwent repeat epithelial debridement in September 2003 and again in October 2003; despite this, epithelial ingrowth worsened (Fig 2 [available at http://aaojournal.org]). By November 2004, the patient’s acuity and quality of vision had again worsened, and he was contemplating penetrating keratoplasty. The second patient had 12-incision RK performed bilaterally in 1993, followed by LASIK in both eyes in June 2001. Epithelial ingrowth occurred, and flap lifts with epi-