Prevalence and causes of low vision and blindness in a rural Southwest Island of Japan: the Kumejima study

Purpose: To determine the prevalence and causes of low vision and blindness in an adult population on a rural southwest island of Japan.

Design: Population-based, cross-sectional study.

Participants: All residents of Kumejima Island, Japan, 40 years of age and older.

Methods: Of the 4632 residents 40 years of age and older, 3762 (response rate, 81.2%) underwent a detailed ocular examination including measurement of the best-corrected visual acuity (BCVA) with a Landolt ring chart at 5 m. The age- and gender-specific prevalence rates of low vision and blindness were estimated and causes were identified.

Main outcome measures: Low vision and blindness were defined, according to the definition of the World Health Organization, as a BCVA in the better eye below 20/60 to a lower limit of 20/400 and worse than 20/400, respectively.

Results: The prevalence of bilateral low vision was 0.58% (95% confidence interval [CI], 0.38-0.89). The primary causes of low vision were cataract (0.11%), corneal opacity (0.08%), retinitis pigmentosa (RP; 0.06%), and diabetic retinopathy (0.06%). The prevalence of bilateral blindness was 0.39% (95% CI, 0.23-0.65). The primary causes of blindness were RP (0.17%) and glaucoma (0.11%). The primary causes of monocular low vision were cataract (0.65%), corneal opacity (0.16%), age-related macular degeneration (0.16%), and diabetic retinopathy (0.11%), whereas those of monocular blindness were cataract (0.29%), trauma (0.25%), and glaucoma (0.22%). Logistic analysis showed that female gender (P = 0.001; odds ratio [OR], 7.37; 95% CI, 2.20-24.71) and lower body weight (P = 0.015; OR, 0.94; 95% CI, 0.90-0.99) were associated significantly with visual impairment.

Conclusions: The prevalences of low vision and blindness in the adult residents of an island in southwest Japan were 1.5 to 3 times higher than the prevalences reported in an urban city on the Japanese mainland. The prevalence of visual impairment caused by RP on this island was much higher than on the mainland, suggesting a genetic characteristic of the population. Furthermore, the prevalence of visual impairment resulting from cataract and corneal opacity was higher than that on the mainland. The prevalence of visual impairment resulting from myopic macular degeneration was less.