Objective: To assess the prevalence and causes of moderate visual impairment in an urban population in southern India.
Design: Population-based, cross-sectional study.
Participants: A total of 2522 (85.4% of the eligible) persons of all ages, including 1399 persons 30 years of age or older, from 24 clusters representative of the population of Hyderabad city.
Testing: The eligible subjects underwent a detailed ocular evaluation, including logarithm of the minimum angle of resolution (logMAR) visual acuity, refraction, slit-lamp biomicroscopy, applanation tonometry, gonioscopy, cataract grading, and stereoscopic dilated fundus evaluation. Automated threshold visual fields and slit-lamp and fundus photography were done when indicated by standardized criteria.
Main outcome measure: Moderate visual impairment was defined as presenting distance visual acuity less than 20/40 to 20/200 or visual field loss by predefined standardized conservative criteria in the better eye.
Results: In addition to the 1% prevalence of blindness in this sample reported earlier, moderate visual impairment was present in 303 subjects, an age-gender-adjusted prevalence of 7.2% (95% confidence interval [CI], 4.5%-9.9%; design effect, 2.7). The major cause of moderate visual impairment was refractive error (59.4%, 95% CI, 52.3%-66.5%) followed by cataract (25.3%, 95% CI, 19%-31.6%). Multivariate analysis showed that the prevalence of moderate visual impairment was significantly higher in those 40 years of age or older (odds ratio, 10.9; 95% CI, 8-15) and females (odds ratio, 1.89; 95% CI, 1.41-2.53) and lower in those belonging to the highest socioeconomic status (odds ratio, 0.27; 95% CI, 0.14-0.51). However, because of the pyramidal age distribution of the population, 38.1% of the total moderate visual impairment was present in those younger than 40 years of age. The proportion of moderate visual impairment caused by refractive error was higher in the younger than in the older age groups (P < 0.0001).
Conclusions: Projecting the results to the 26.5% urban population of India, there would be 18.4 million (95% CI, 11.5-25.2 million) persons with moderate visual impairment in urban India alone. Refractive error was the major cause of moderate visual impairment in the population studied. The absolute proportion of moderate visual impairment in those younger than 40 years of age was considerable. The eyecare policy of India, apart from dealing with blindness, should address the issue of the relatively easily treatable uncorrected refractive error as the cause of moderate visual impairment in an estimated 10.9 million persons in urban India.