Anisometropia shows an exponential increase in prevalence with increasing age based on cross-sectional studies. The purpose of this study was to evaluate longitudinal changes in anisometropia in all refractive components in older observers and to assess the influence of early cataract development.
Refractive error was assessed at two time points separated by approximately 12 years in 118 older observers (aged 67.1 and 79.3 years at the two test times). Anisometropia defined as greater than or equal to 1.00 D was calculated for all refractive components. The subjects had intact ocular lenses in both eyes throughout the study. Lens evaluations were performed at the second test using the Lens Opacities Classification System III.
All refractive components approximately doubled in prevalence of anisometropia. Spherical equivalent anisometropia changed from 16.1 to 32.2%. Similar changes were found for spherical error (17 to 38.1%), primary astigmatism (7.6 to 17.8%), and oblique astigmatism (14.4 to 29.7%). Many who did not have anisometropia at the first visit subsequently developed anisometropia (e.g., 26.3% for spherical error and 22.9% for oblique cylinder). The onset of anisometropia occurred at all ages within the studied age range, with no particular preference for any one age. A small number lost anisometropia over time. Individual comparisons of refractive error changes in the two eyes in combination with nuclear lens changes showed that early changes in nuclear sclerosis in the two eyes could account for a large proportion of anisometropia (∼40%), but unequal hyperopic shift in the spherical component in the two eyes was the primary cause of the anisometropia.
Anisometropia is at least 10 times more common in the elderly than in children, and anisometropia develops in all refractive components in the oldest observers. Clinicians need to be aware of this common condition that could lead to binocular vision problems and potentially cause falls in the elderly.