Assessment of Macular Recovery Time After Photostress by Foveal L-Cone Dark Adaptation in Young and Old Subjects

Abstract

Purpose: : Several studies have shown that macular recovery time (MRT) after photostress increases as a function of age and is prolonged in the context of several retinal diseases. However, the value of this technique for assessing retinal function has been limited by the lack of standardized methods and limited reliability. After evaluation of several methods of applying photostress and assessing recovery, we have developed a novel, reproducible method and assessed MRT in young and old subjects.

Methods: : MRT after photostress was assessed in 10 eyes of 10 subjects (5 aged 20-29, 5 aged 60; BCVA of ≥ 20/20). After assessing baseline cone threshold, photostress was applied with a diffused fluorescent light source of ~40,000 cd/m² viewed for 90 seconds from a distance of 12 inches. This exposure was safe (2200-fold lower than the damage threshold determined by analysis of the emission spectrum of the lamp) and sufficient to bleach 90-95% of cone photopigment. Baseline cone threshold and MRT after photostress were assessed by foveal L-Cone dark adaptation. All subjects were tested 3 times within 2 weeks. For each subject and trial, baseline cone thresholds and recovery half-lives were estimated using exponential models. The reliability of the estimates of each of these parameters was assessed via a components of variance model and intraclass correlation coefficient (ICC). The effects of age on baseline cone threshold and recovery half-life were assessed via an exponential model with fixed effects for age and random effects for subjects.

Results: : ICC estimates of 0.61 and 0.68 indicated substantial reliability for baseline cone threshold and recovery half-life, respectively. The older population had a slightly higher mean baseline cone threshold (-1.84 vs. -1.96 log cd/m²; p=0.055) and a substantially longer mean recovery half-life (91 seconds vs. 58 seconds; p = 0.008).

Conclusions: : We have developed a reliable method for assessment of MRT after photostress, and observed a significantly increased recovery half-life in older subjects compared to younger subjects. We are investigating the utility of this method as a quantitative measure of macular function in the context of retinal diseases such as AMD.

Keywords: aging: visual performance • computational modeling • photoreceptors: visual performance