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Tom H Margrain, Nicola Cassels, Alison M Binns, Ashley Wood; Rod and cone visual pigment synthesis rates are abnormal in iAMD and dependent on underlying pathology. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3439. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
High fidelity imaging retinal densitometry (IRD) is a new technique that can measure visual pigment synthesis rates topographically across the central retina. The purpose of this study was to: 1) compare rod and cone visual pigment synthesis rates in a small group of people with and without intermediate stage age-related macular degeneration (iAMD) and, 2) to examine the relationship between pigment synthesis rates and underlying retinal pathology.
By measuring retinal reflectance before and after photobleaching, IRD is able to quantify visual pigment synthesis rates across the central retina. Multispectral reflectance images of the central retina (20°) were obtained for one minute before and for ten minutes after exposure to a ‘white’ light that bleached >95% of rod and cone visual pigment. By fitting the post bleach density difference spectra with known rod and cone absorption spectra the optical density of each photoreceptor type was recovered over space and time. The optical density data was modelled using a rate limited function to produce heat maps that describe topographical differences in rod and cone visual pigment synthesis rates. This functional information was compared to structural information based on colour fundus photography and SD OCT imagery. Five healthy controls and 5 people with iAMD took part in the study.
The cone data was extracted from the fovea and the rod data from within an annulus (6°-8°). For rod photoreceptors, the recovery rate per molecule in healthy older adults was v=0.079 SD 0.024 min-1 and for cones v=0.206 SD 0.069 min-1. For those with iAMD the recovery rates per molecule were slower, with average values for rods and cones being v = 0.043 SD 0.019 min-1 and v=0.119 SD 0.046 min-1, respectively. Topographical differences in recovery rates were found to map onto underlying pathological features such as drusen, subretinal drusenoid deposits and ellipzoid zone boundary disruption.
Rod and cone visual pigment synthesis rates in people with iAMD are slower than in healthy controls. In those with iAMD, topographical differences in pigment synthesis rates are often but not always related to underlying structural abnormalities.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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