Normal aging: capturing changes in contrast acuity at low light levels

Abstract

AbstractPurpose Visual tasks that require discrimination of fine spatial detail become a challenge to older subjects, particularly when the light level is low. This worsening of vision is increased further when diseases of the eye are also involved, and these effects are difficult to separate. An index to describe the health of the retina (HRindex) by capturing how contrast acuity (CA) worsens as a function of light level is introduced and the statistical limits of variability established in normal eyes.Methods CA thresholds were measured at five light levels (in the rage 0.12 to 34 cd/m^2) in 80 subjects, aged 18‐80 years using the CA assessment test (ASEM, 74, 551‐559, 2003). Long wavelength light was used to minimise variability. Stimuli were presented at 0 and ±4 degrees. Pupil size was measured throughout and used to calculate subject‐specific retinal illuminances. The measurements were carried out binocularly and monocularly and in addition to clinical examination, a number of filters were also used to screen for normal eyes.Results The HRindex was calculated for each subject using a method similar to that developed to investigate changes in colour vision (JOSA, 29 (2):27‐35, 2012). Limits for CA have been established for normal eyes. The effects of aging were examined as well as differences between binocular and monocular thresholds and retinal location.Conclusion The results show that when appropriate screening for normal vision is applied the HRindex becomes largely independent of age. The new approach and the limits of normal vision obtained in this study make it possible to screen for early‐stage, subclinical retinal disease using CA assessment.