Rod and Cone Mediated Function in Retinal Disease

National Eye Institute

Investigators

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Abstract

The first two Aims of this protocol require establishing the normal ranges for dark-adapted retinal sensitivity and the kinetics of dark adaptation using a new instrument, the Medmont dark-adapted chromatic (DAC) perimeter. Specific Aim 1: To establish the normal ranges of dark-adapted retinal sensitivities for the Medmont red and blue stimuli in healthy volunteers. With 2-color dark-adapted perimetry, calculation of the difference in dark-adapted retinal sensitivity to blue and red stimuli is fundamental to determining whether a sensitivity at a given retinal location is mediated by rods and/or cones. We have collected 2-color dark-adapted perimetry thresholds with the Medmont from 17 healthy volunteers (HVs) ranging in age from 16-53 years. Specific Aim 2: To establish the normal ranges for the kinetics of dark adaptation for the Medmont DAC blue and red stimuli in healthy volunteers. The time course of dark adaptation has historically been measured clinically following exposure to an achromatic background light that bleaches approximately 50-100% of rhodopsin. Given that dark adaptation can be very delayed (several hours) in patients with AMD and some genetic disorders (e.g. Fundus Albipunctatus) and many patients with retinal degenerations have marked photo aversion, we are seeking to examine the kinetics of dark adaptation to smaller bleaches. To date, we have measured the kinetics of dark adaptation with the Medmont from 15 healthy volunteers using a 30% bleach Specific Aim 3: To quantify local changes in rod and cone photoreceptor function across the retina in participants with retinal disease. We examined scotopic thresholds and dark-adaptation (DA)in AMD participants who were categorized into five AMD severity groups based on fundus features. The major finding of our study was the identification of three rod-function phenotypes. Normal rod function (RF1), normal thresholds but slowed DA (RF2), and elevated DA thresholds with slowed DA kinetics (RF3). We believe these three phenotypes into underlying changes in rod photoreceptor function and the delivery of the 11-cis-retinal to rods is affected differentially in participants with AMD.