The Effect of Trabeculectomy on Lens Opacity in Asian People

Abstract

Abstract: : Purpose: To examine the natural history of lens opacity changes in a large cohort of Asian people in a prospective study of trabeculectomy. Methods: Singaporean subjects with open–angle and angle–closure glaucoma were enrolled in a prospective study of the long–term effect of trabeculectomy. Baseline data recorded included past medical and ophthalmic history, medications and ocular examination. Cataract was graded at the slitlamp by ophthalmologists using a modification of the Lens Opacity Classification System (LOCS) III, with subjects’ pupils fully dilated. Lens grading was carried out at baseline and yearly thereafter. The main outcome measure (‘Any cataract’) was worsening of lens opacity or having had cataract surgery. A lens opacity was said to have worsened if the LOCS score for any of the 3 regions (nuclear, cortical or posterior sub–capsular) increased by 2 units or more. Secondary outcome measures were taken as worsening of the LOCS score by 2 or more units in each of the 3 regions of the lens. Cox regression with backward model selection at 0.10 removal level was used to determine risk factors. Results: 241 subjects were included in this study. 148 subjects (61%) reached outcome ‘Any cataract’. Median time to outcome was 12 months (range 1–57 months). In the multivariate analysis, being operated by a trainee surgeon was 50% (95% CI 5 –114%) more likely to result in the earlier development of cataract or need for cataract surgery than being operated by a specialist. Having at least one episode of hypotony in the first 3 months post–surgery increased the risk by 39% ( 95% CI 0 – 92%). A mean increase of 1 drop per day of prednisolone forte over the first 9 months post trabeculectomy increased the risk by 8% (95% CI 0 – 18%). An increase in age of 1 year increased the risk by 5% (95% CI 3 – 7%). Previous use of topical pilocarpine increased the risk of developing worsening of lens opacity in the nuclear and posterior subcapsular regions by 178% (95% CI 93–728%) and 68% (95% CI 1–179%) respectively. Conclusions:This study has highlighted a number of risk factors associated with the development of lens opacity in Asian people who have had trabeculectomy. This has a clinical relevance since it suggests that avoiding use of pilocarpine for long periods pre–operatively, avoiding postoperative hypotony, being operated on by a senior glaucoma specialist and judicious use of postoperative steroid may delay the onset of cataract.

Keywords: clinical (human) or epidemiologic studies: risk factor assessment • cataract