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A.V. Cideciyan, T.S. Aleman, M. Swider, E.E. Smilko, S.B. Schwartz, J.D. Chico, M.G. Maguire, J. Bennett, E.M. Stone, S.G. Jacobson; Delay of Rod Dark Adaptation Correlates with the Extent of Local Disease in ABCA4-associated Retinal Degenerations . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4862.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: ABCA4 codes for ABCR, a disc rim protein hypothesized to accelerate recovery of photoreceptor sensitivity by contributing to the removal of all-trans-retinal released from rod and cone visual pigments after light exposure. We correlated the kinetics of rod and cone dark adaptation with measures of retinal function and structure in patients with mutations in ABCA4 gene. Methods: Patients were examined clinically, and with dark- and light-adapted static perimetry, and ERG photoresponses. Preferred locus of fixation was determined under fundus visualization. Psychophysical dark adaptation was performed at one or two retinal loci and quantified in terms of threshold elevation and time to criterion recovery. Recovery kinetics of rod photoreceptor function across the retina was estimated with an abbreviated two-flash paradigm. Retinal structure data was estimated with optical coherence tomography (OCT) and autofluorescence imaging. Results: Clinical disease spectrum of the patients ranged from mild maculopathy to severe widespread retinal degeneration (n=38; age=11-73yrs; VA=-0.1 to 2 log MAR). ERGs ranged from normal to non-detectable and psychophysical thresholds from normal to profoundly elevated. Mean peripheral (>30 deg ecc.) rod (RSL) and cone sensitivity losses (CSL) were highly correlated and tended to show a greater rod than cone loss. The delay of rod dark-adaptation ranged from 19 to 71 minutes (normal=17-23 min) and correlated highly (r2=0.8) with RSL measured at the same retinal location (~20 min delay per log of RSL). In a subset of the patients, dark adaptation performed at multiple locations showed intraretinal variation of rod delay that also correlated with local RSL. Local measures of structure implicated loss of RPE and photoreceptors as a cause for the local RSL. There was no correlation between dark adaptation delay measured locally with psychophysics and photoreceptor deactivation delay estimated across the retina with ERG photoresponses. Conclusions: Normal kinetics of rod and cone dark adaptation observed in many patients with ABCA4-associated retinopathies argues against a visual cycle abnormality as a universal consequence of this molecular defect. The finding of co-localized loss of RPE and photoreceptors complicates the interpretation of the delay in rod visual cycle in some of the human ABCA4-associated retinopathies.
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