Critical Flicker Fusion Recovery Following Photo-Bleach in Young and Old Subjects

Abstract

Purpose : Critical flicker fusion (CFF) is a measure of visual processing speed. We examined CFF threshold at specific time-points after photo-bleach in order to assess age-dependent cone recovery over time.

Methods : Photo-bleaching employed a 90-second exposure to a specialized light source delivering 40,000 cd/m². This method was independently confirmed to provide bleaching of >84% of cones. Baseline CFF (repeat testing) was obtained for one eye at 100% device luminance using a mean value derived from both increasing and decreasing frequency staircases. Post-bleach CFF testing was measured at 30 seconds and at 1½, 2½, and 3½ minutes using 2 luminance levels: photopic (44 cd/m²) or mesopic (4.4 cd/m²).

Results : Ten subjects who completed the protocol were grouped into young (mean 24.3), middle (mean 39.8) and old (mean 60.3) cohorts, and mean CFF values were calculated for each group at each time point. CFF measured with photopic luminance showed an age-dependence to recovery, with the older patients exhibiting an 8.9% initial decrease (p=0.017), while subjects in the youngest cohort decreased by 4.3% (p=0.136). All subjects returned to baseline within 150 seconds, and all groups exhibited a characteristic overshoot in which CFF threshold was increased relative to baseline. For mesopic testing, younger patients showed the largest decrease in CFF following photobleach (13.5%, p=0.001). At the lower luminance, there was a sustained decrease in CFF.

Conclusions : Recovery of CFF after photobleach appears to be age-dependent. Under photopic luminance, older individuals exhibit a greater change and longer recovery time. At lower, mesopic luminance, older subjects show a lesser effect on thresholds, although recovery times are similar for all ages.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.