Assessment of age changes and repeatability for computer-based rod dark adaptation

PURPOSE: To characterize the rate of rod-mediated sensitivity decline with age using a PC-driven cathode ray tube (CRT) monitor. To provide data regarding the repeatability of the technique. METHODS: Dark adaptation was monitored for 30 min following a minimum 30 % pigment bleach, using a white 1° stimulus (modulated at 1 Hz), presented 11° below fixation on a CRT monitor. Thirty-three subjects with no ocular pathology and normal fundus photographs were divided into two groups: older (≥45, n = 16) and younger (<45, n = 17). RESULTS: Rod recovery was assessed using component S2 of dark adaptation. S2 was significantly slower in the older (0.19 ± 0.03 log cd.m(−2).min(−1)) compared with the younger group (0.23 ± 0.03 log cd.m(−2).min(−1), t = −4.05, p < 0.0003), despite no difference in visual acuity and fundus appearance. Faster rates of S2 recovery were correlated with lower threshold at 30 min (T(30)) (r = −0.49). Correlation coefficients between first and second measurements for S2 and T(30) were 0.49 (p < 0.009) and 0.84 (p < 0.0001) respectively. The coefficient of repeatability was 0.07 log cd.m(−2).min(−1) for S2 and 0.35 log cd.m(−2) for T(30). The coefficients of variation for S2 and T(30) were 15 % and 10 % respectively. CONCLUSIONS: Dark adaptation is slowed in normal ageing. CRT-based dark adaptometry is easily implemented and highly repeatable. The technique described in this article would be useful for documenting visual changes in future clinical trials assessing retinal health in the older eye with and without ocular pathology.