A novel technique for measuring dark adaptation using a dual stimulus method: Effects of aging and AMD on dark adaptation

Abstract

Purpose To study abnormal dark adaptation (DA) in aging and macular degeneration (AMD) using a new technique that measures DA at two retinal locations by using a dual stimulus. To establish whether there are localized regions of impaired rod function, especially the rate of the rod‐mediated recovery (S2) as it has been previously suggested Methods Dual arc‐shaped white stimuli were presented on a black CRT monitor at locations 6º and 11º of eccentricity in the inferior visual fiel. Recovery of sensitivity to the two stimuli was measured concurrently using the method of adjustment, following a bleaching exposure of at least 30%. The dynamic range of the CRT was expanded using ND filters. DA curves were obtained after fitting the data by non‐linear regression to a seven‐parameter model. Three groups of observers (young, older and AMD) were tested to detrmine any differences between them and the effect of the testing location, focusing on parameters α (rod‐cone break) and S2 (slope of the post‐ α phase of rod recovery) Results Both stimuli produced matched cone recovery curves within each group. Comparing groups (young vs. older) and (older vs. AMD), we found significant differences in the two DA parameters studied here. Regarding the AMD group, we found a trend in both parameters to be more affected at 6º than at 11º, however, these differences were not significant Conclusion This technique has shown to be sensitive to detect changes in rod recovery in AMD patients compared to healthy subjects and allows the measurement of DA in two retinal locations simultaneously. It may help in the early diagnosis and monitoring of degenerative diseases of the macula, which are increasingly common

The Light and the Dark of Early and Intermediate AMD: Cone- and Rod-Mediated Changes Are Linked to Fundus Photograph and FAF Abnormalities

“…DA was measured psychophysically using a PC-based system as previously described. 39,40,[54][55][56][57] The test was conducted monocularly in the study eye. The subjects wore their best optical correction for the test distance (90 cm), and the fellow eye was covered using an eye patch.…”

“…33,34 The ratio of cones to rods in the macula is approximately 9:1, 35 and it is therefore likely that, by the time patients notice changes in their photopic vision, they will have lost many millions of rods. 34,[36][37][38][39][40] Classically, the dynamics of cone and rod function are assessed by exposing the eye to a photobleach and plotting the recovery of sensitivity against time. As has been known for many years, [41][42][43] this sensitivity recovery function, called the dark adaptation (DA) curve, is composed of cone and rod components.…”