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G.M. Gazzard, P.J. Foster, S. Saw, J. Devereux, P.T. Khaw, S. Seah; Lens Thickness, Lens Position and Peripheral Anterior Synechiae in the Singaporean and Mongolian Glaucoma Prevalence Surveys . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3404.
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Purpose: Previous clinic-based studies have suggested primary angle closure and peripheral anterior synechiae (PAS) to be associated with a large and/or anterior lens leading to a shallow anterior chamber. We aimed to investigate the influence of lens thickness (LT) and lens position on the rate of PAS in two Asian populations with a high prevalence of primary angle closure glaucoma. Methods: Representative, population-based data were gathered on Mongolian and Singapore-Chinese subjects over 40 years in two glaucoma prevalence surveys. Axial length (AL) & lens thickness (LT) were measured by A-scan ultrasound and anterior-chamber depth by optical pachymetry. Outcome measures: absolute lens position (ALP) = ACD + LT/2 (mm), relative lens position (RLP)= (ACD + LT / 2) / AL (no units), and peripheral anterior synechiae diagnosed on dynamic gonioscopy. Results: 2802 subjects were assessed, 1090 Singaporean Chinese (497 males, 593 females) & 1712 in Mongolia (743 males, 969 females). The crude rate of PAS was 8.8% (95% confidence interval (CI) 7.8, 9.9) overall: 9.6% (95% CI 7.8, 11.3) in Singapore & 8.4% (95% CI 7.0, 9.7) in Mongolia. The rate increased significantly with age, was higher in women & showed differences between the two populations. The risk of PAS increased with LT and more anteriorly positioned lenses in both groups. After adjusting for age and gender only, each mm increase in LT conferred a 2.5 times (95% CI 1.8, 3.5) greater risk, (p < 0.001). Eyes with ALP ≤ 4.79mm had a 3.3x (95% CI 2.2, 4.6) greater risk & eyes with RLP ≤ 0.21 had a 2.0 times (95% CI 1.5, 2.8) greater risk of PAS than eyes with less anterior absolute or relative lens positions. In a multivariate model controlling for lens thickness, axial length, age, sex and country of origin ACD was the only significant predictor of PAS (p<0.001). Conclusion: The risk of PAS in these Asian subjects increased with larger and more anterior lenses, an effect likely mediated by a shallower anterior chamber leading to increased chance of iris / trabecular meshwork apposition
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