Background: The Blue Mountains Eye Study is a population-based study of vision and the causes of visual impairment and blindness in a well-defined urban, Australian population 49 years of age and older.

Methods: The logarithm of the minimum angle of resolution (logMAR) visual acuity was measured before and after refraction in 3647 persons, representing an 88% response rate in two postcode areas in the Blue Mountains area, west of Sydney.

Results: Refraction improved visual acuity by one or more lines in 45% of participants and by three or more lines in 13%. Visual impairment (visual acuity 20/40 or worse in the better eye) was found in 170 participants (4.7%). Mild visual impairment (Snellen equivalent 20/40 to 20/60 in the better eye) was found in 3.4%, moderate visual impairment (20/80 to 20/160 in the better eye) in 0.6%, and severe visual impairment or blindness (20/200 or worse in the better eye) in 0.7%. Visual impairment increased with age from 0.8% of persons 49 to 54 years of age to 42% of persons 85 years of age or older. Visual impairment was significantly more frequent in females at all ages. Among persons with severe visual impairment, 79% were female. After adjusting for age, females were less likely to achieve 20/20 best-corrected visual acuity than males (odds ratio, 0.57; confidence interval, 0.48-0.66). After adjusting for age and sex, no association was found between visual acuity and socioeconomic status. Age-related macular degeneration was the cause of blindness in 21 of the 24 persons with corrected visual acuity of 20/200 or worse.

Conclusion: Increasing age and female sex were independent predictors of visual impairment.