The role of dark adaptation in understanding early AMD.

From PubMed via Jisc Publications RouterHistory: received 2021-04-21, revised 2021-09-24, accepted 2021-09-29Publication status: aheadofprintThe main aim of the paper is to discuss current knowledge on how Age Related Macular Degeneration (AMD) affects Dark Adaptation (DA). The paper is divided into three parts. Firstly, we outline some of the molecular mechanisms that control DA. Secondly, we review the psychophysical issues and the corresponding analytical techniques. Finally, we characterise the link between slowed DA and the morphological abnormalities in early AMD. Historically, DA has been regarded as too cumbersome for widespread clinical application. Yet the technique is extremely useful; it is widely accepted that the psychophysically obtained slope of the second rod-mediated phase of the dark adaptation function is an accurate assay of photoreceptor pigment regeneration kinetics. Technological developments have prompted new ways of generating the DA curve, but analytical problems remain. A simple potential solution to these, based on the application of a novel fast mathematical algorithm, is presented. This allows the calculation of the parameters of the DA curve in real time. Improving current management of AMD will depend on identifying a satisfactory endpoint for evaluating future therapeutic strategies. This must be implemented before the onset of severe disease. Morphological changes progress too slowly to act as a satisfactory endpoint for new therapies whereas functional changes, such as those seen in DA, may have more potential in this regard. It is important to recognise, however, that the functional changes are not confined to rods and that building a mathematical model of the DA curve enables the separation of rod and cone dysfunction and allows more versatility in terms of the range of disease severity that can be monitored. Examples are presented that show how analysing the DA curve into its constituent components can improve our understanding of the morphological changes in early AMD. [Abstract copyright: Copyright © 2021. Published by Elsevier Ltd.

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