An Alternative Psychophysical Diagnostic Indicator of the Aging Eye.

John D Rodriguez,Garrick Wallstrom,Donna Welch,Mark B Abelson,Divya Narayanan

doi:10.1155/2019/2036192

John D Rodriguez, Garrick Wallstrom + Show 3 more

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https://doi.org/10.1155/2019/2036192

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Abstract

Purpose Impaired adaptation to changes in lighting levels as well as mesopic visual function is a common complaint in those over the age of 65. The use of photostress is a well-established method to test the adaption rate and the response of the visual cycle. In this study, we test visual function recovery to mesopic luminance stimuli following a long duration photostress in young and elderly subjects. If successful in strongly differentiating aging macular function, these methods may also be useful in the study of pathologies such as age-related macular degeneration. Methods A group of 12 older normal subjects (mean age 75.1 ± 4.79) and a control group of 5 younger normal subjects (mean age 26.2 ± 4.19) were subjected to macular photostress using the OraLux photostress system. The OraLux system provides a diffuse light source bleaching 84% of cone photopigment while maintaining an exposure safety factor of 200 times less than the maximum safe exposure. After each photostressing session, macular recovery was tracked using a foveal, variable contrast, flickering stimulus of mean luminance in the high mesopic range. Recovery was tracked for 300 seconds. The endpoint was time to recovery to each individual's baseline sensitivity as determined by two static sensitivity trials prior to photostress. Results Proportional hazards analysis of recovery time yielded a statistically significant difference between the older group and the young group (HR = 0.181; p=0.0289). The estimated hazard ratio of 0.181 indicates that older subjects return to baseline at less than one-fifth the rate of younger subjects. The hazards ratio remained statistically significant after adjusting for visual acuity (HR = 0.093; p=0.0424). Conclusion Photostress recovery of flicker sensitivity under mesopic conditions is a strong differentiator of aging macular function. This agrees with subject-reported complaints in reduced luminance conditions after exposure to bright lights such as night driving. The qualitative similarity between the aging retina and changes in early AMD suggests that flicker recovery following photostress may be useful as a surrogate endpoint in AMD clinical trials.

Highlights

In contrast to previous studies on photostress in normal subjects, in which recovery endpoints based on visual acuity were used, the recovery endpoint used here is a flickering foveal blob presented on a computer screen with mesopic luminance background
This endpoint is useful for assessing the health of the aging retina due to its relative insensitivity to defects in the ocular media. e combination of photostress and flicker constitute a retinal stress test which stresses the visual cycle and retinal metabolism
We find that using a mesopic flicker recovery target followed by our high bleach photostress system strongly differentiates aging macular function

Summary

Introduction

Retinal diseases may result in diminished robustness of the visual cycle and adaptation to changing light levels Both age-related macular degeneration (AMD) and diabetic retinopathy have been shown to be important examples [5, 6, 10,11,12,13,14]. E use of photostress in this context is as a stress test of the visual cycle analogous to the widely used cardiovascular stress test in order to more detect pathology in the early disease state Both aging and AMD have been shown to result in rod photoreceptor loss and diminished sensitivity in short wavelength (blue) photoreceptors [15, 16].

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