Baseline risk factors for incidence of blindness in a South Indian population: The Chennai eye disease incidence study

PURPOSE. To report the baseline risk factors and causes for incident blindness.

METHODS. Six years after the baseline study, 4419 subjects from the cohort underwent a detailed examination at the base hospital. Incident blindness was defined by World Health Organization criteria as visual acuity of less than 6/120 (3/60) and/or a visual field of less than 108 in the better-seeing eye at the 6-year follow-up, provided that the eye had a visual acuity of better than or equal to 6/120 (3/60) and visual field greater than 108 at baseline. For incident monocular blindness, both eyes should have visual acuity of more than 6/120 (3/60) at baseline and developed visual acuity of less than 6/120 (3/60) in one eye at 6-year follow-up.

RESULTS. For incident blindness, 21 participants (0.48%, 95% confidence interval [CI], 0.3–0.7) became blind; significant baseline risk factors were increasing age (P = 0.001), smokeless tobacco use (P < 0.001), and no history of cataract surgery (P = 0.02). Incident monocular blindness was found in 132 participants (3.8%, 95% CI, 3.7–3.8); it was significantly more (P < 0.001) in the rural population (5.4%, 95% CI, 5.4–5.5) than in the urban population (1.9%, 95% CI, 1.8–1.9). Baseline risk factors (P < 0.001) were increasing age and rural residence, and no history of cataract surgery was a protective factor (P = 0.03).

CONCLUSIONS. Increasing age was a significant risk factor for blindness and monocular blindness. No history of cataract surgery was a risk factor for blindness and a protective factor for monocular blindness.