Age-specific prevalence and causes of bilateral and unilateral visual impairment in older Australians: the Blue Mountains Eye Study

Purpose: To report age-specific prevalence and causes of bilateral and unilateral visual impairment in a representative older Australian population. Methods: Participants in the Blue Mountains Eye Study (n = 3654) underwent a detailed eye examination. Any visual impairment was defined as best-corrected visual acuity (VA) of 6/12 or worse, moderate impairment as VA 6/24-6/60 and severe impairment as VA worse than 6/60 (the Australian definition for legal blindness). Bilateral visual impairment was defined from the better eye and unilateral impairment from the worse eye. Proportional causes for visual loss were determined by the examining ophthalmologist. Results: Prevalence of bilateral and unilateral visual impairment was strongly age related. Corresponding bilateral and unilateral visual impairment prevalence rates were, respectively, 0.6% and 3.6% for persons aged 49-59 years, 1.1% and 8.2% for ages 60-69, 5.4% and 20.1% for ages 70-79, and 26.3% and 52.2% for persons aged 80+ years. Overwhelmingly, age-related maculopathy (ARM) was the predominant cause of bilateral blindness (13/17) and of moderate to severe bilateral visual impairment in persons aged 70+ years. However, cataract was the most frequent cause of mild bilateral visual impairment among persons aged 60+ years. Amblyopia was the most frequent cause of mild or worse unilateral visual impairment in persons aged 49-59 years. Cataract was the most common cause of mild unilateral visual impairment in people aged 60+ years, while ARM and cataract were jointly the most frequent causes of moderate to severe unilateral visual impairment in people aged 70+ years. Conclusions: These findings indicate that around half of visually impaired persons aged 60 years or over had cataract, a cause amenable to treatment.