Differential associations of myopia with major age-related eye diseases: the Singapore Indian Eye Study.

Purpose: To determine the associations of myopia and axial length (AL) with major age-related eye diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), age-related cataract, and primary open-angle glaucoma (POAG).
Design: Population-based, cross-sectional study.
Participants: A total of 3400 Indians (75.6% response rate) aged 40 to 84 years in Singapore.
Methods: Refractive error was determined by subjective refraction, and AL was determined by noncontact partial coherence laser interferometry. Age-related macular degeneration and DR were defined from retinal photographs according to the Wisconsin Age-Related Maculopathy Grading System and Airlie House classification system, respectively. Age-related cataract was diagnosed clinically using the Lens Opacity Classification System (LOCS) III system. Glaucoma was defined according to International Society for Geographical and Epidemiological Ophthalmology criteria.
Main Outcome Measures: Age-related macular degeneration, DR, age-related cataract, and POAG.
Results: Myopic eyes (spherical equivalent [SE] <-0.5 diopter [D]) were less likely to have AMD (early plus late AMD) (odds ratio [OR], 0.45; 95% confidence interval [CI], 0.25-0.79) or DR (OR, 0.68; 95% CI, 0.46-0.98) compared with emmetropic eyes; each millimeter increase in AL was associated with a lower prevalence of AMD (OR, 0.76; 95% CI, 0.65-0.89) and DR (OR, 0.73; 95% CI, 0.63-0.86). Myopic eyes were more likely to have nuclear (OR, 1.57; 95% CI, 1.13-2.20) and posterior subcapsular (OR, 1.73; 95% CI, 1.10-2.72) cataract, but not cortical cataract (P = 0.64); each millimeter increase in AL was associated with a higher prevalence of posterior subcapsular cataract (PSC) (OR, 1.29; 95% CI, 1.07-1.55), but not nuclear (P = 0.77) or cortical (P = 0.39) cataract. Eyes with high myopia (SE <-6.0 D) were more likely to have POAG (OR, 5.90; 95% CI, 2.68-12.97); each millimeter increase in AL was associated with a higher prevalence of POAG (OR, 1.43; 95% CI, 1.13-1.80).
Conclusions: Myopic eyes are less likely to have AMD and DR but more likely to have nuclear cataract, PSC, and POAG. The associations of myopia with AMD, DR, and POAG are mostly explained by longer AL. However, the association between myopia and nuclear cataract is explained by lens refraction rather than AL.
(Copyright © 2013 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.)