Causes of incident visual impairment: the Blue Mountains Eye Study

To describe the causes of 5-year incident visual impairment and doubling of the visual angle in a population-based cohort.

Of the 3654 participants aged older than 50 years who participated in the Blue Mountains Eye Study (BMES I, 1992-1994), 543 died and 2335 were reexamined between 1997 and 1999 (BMES II). Visual acuity was measured using a logMAR chart before and after refraction. Pupils were dilated, and a detailed eye examination was performed. For participants with incident visual impairment or doubling of the visual angle, an ophthalmologist attributed and proportioned causes. Primary causes were defined as those responsible for 50% or more of the impairment.

After refractive correction, the proportion of incident bilateral impairment worse than 20/40, worse than 20/70, and worse than 20/200 that were caused primarily by cataract decreased from 51.4% (n = 19) to 40.0% (n = 6) to 0%; while the proportion of cases caused primarily by age-related maculopathy increased from 24.3% (n = 9) to 33.3% (n = 5) to 100.0% (n = 2). Similarly, the corresponding proportions of incident unilateral impairment caused primarily by cataract decreased from 53.7% (n = 72) to 36.9% (n = 31) to 13.6% (n = 6); meanwhile, the proportion of cases caused primarily by age-related maculopathy increased from 19.4% (n = 26) to 32.1% (n = 27) to 54.5% (n = 24). The proportions of persons with incident bilateral impairment worse than 20/40, worse than 20/70, and worse than 20/200 that could be improved with refraction were 79.4% (n = 143), 73.6% (n = 42), and 0%, respectively. The corresponding proportions of incident unilateral impairment improved by refraction were 66.7% (n = 269), 59.0% (n = 121), and 21.4% (n = 12).

This study has documented the 5-year incidence and causes of visual impairment in an older Australian population.