Five-year change in visual acuity and incidence of visual impairment - The Blue Mountains Eye Study

Purpose: To describe the 5-year change in visual acuity and the incidence of visual impairment in a population-based cohort. Design: Population-based epidemiologic study. Participants: Of the 3654 participants of the Blue Mountains Eye Study (BMES I) baseline examination (aged 49 years+ during 1992-1994), 2335 were reexamined during the 5-year follow-up examinations from 1997 to 1999 (BMES II), and 543 persons had died since BMES I. Methods: Visual acuity was measured using a logarithm of the minimum angle of resolution chart in both eyes separately before and after standardized refraction. Pupils were dilated and a detailed examination was performed. Main Outcome Measures: Visual impairment, after best refractive correction, was defined as any (visual acuity less than or equal to 20/40; less than or equal to 41 letters) and severe (visual acuity less than or equal to 20/200; 0-5 letters) in keeping with the Beaver Dam Eye Study. Incident binocular visual impairment was defined as visual acuity less than or equal to 20/40 in both eyes at follow-up, where visual acuity was > 20/40 in both eyes at baseline. Incident binocular severe visual impairment was defined as visual acuity less than or equal to 20/200 in both eyes at follow-up, where visual acuity was > 20/200 in both eyes at baseline. The incidence for three other levels of visual impairment is also given: < 20/40, < 20/70, and < 20/200. Monocular visual impairment was defined as impairment in one eye only at follow-up, where both eyes were unimpaired at baseline. Incident doubling and halving of the visual angle were calculated. Results: Incidence rates for visual impairment increased significantly with age. Any incident impairment less than or equal to 20/40 occurred binocularly in 41 persons (1.9%) and monocularly in 150 persons (7.1%). Severe incident impairment less than or equal to 20/200 occurred binocularly in 3 persons (0.1%) and monocularly in 44 persons (2.1%). Incident impairment < 20/40 occurred binocularly in 37 persons (1.7%) and monocularly in 134 persons (6.3%). Impairment < 20/70 occurred binocularly in 15 persons (0.7%) and monocularly in 84 persons (3.8%). Impairment < 20/200 occurred binocularly in 3 persons (0.1%) and monocularly in 44 persons (1.9%). Women consistently had a higher incidence of visual impairment than men, although this was often. not statistically significant after adjusting for age. Increasing age was a strong predictor of visual impairment. Conclusions: This study has documented the 5-year incidence and causes of visual impairment in an older Australian population.