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P. Kozma, C.D. Bathia, D.C. Hood, D.G. Birch; Central Rod and Cone A–Wave Parameters in Macular Forms of Photoreceptor Degeneration . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4559.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To record both rod and cone photoreceptor ERG responses from the central retina in patients with Stargardt macular dystrophy and age–related macular degeneration (AMD), diseases that selectively affect the central retina. Methods: Dark– and light–adapted full–field and central rod and cone a–wave responses were obtained to high intensity white flashes in 8 subjects with Stargardt disease (mean age: 31.5 yrs) and 10 subjects with early stages of dry AMD (mean age 68.5 yrs). Patients’ data were compared to 7 normal controls (mean age: 31.6 yrs). The four flash intensities ranged from 3.2 to 4.4 log scot td–s (2.8 to 4.0 log phot td–s). All responses were obtained in a Ganzfeld dome. Central dark– and light adapted responses were recorded at a viewing distance of 0.25 m where the opening of the dome subtended 40 degrees. To obtain focal rod a–waves, the four flash intensities were presented in the dark followed by a double flash series. Subtraction of the double–flash responses eliminated the stray light and the cone component. To record focal cone a–waves, the single flashes were presented on a background of 3.2 log td–s. The stray light was masked with a retina–wide 3.6 log td–s surrounding light field. Results: Maximum receptor amplitudes (RmP3) of the full–field rod and cone responses were comparable to normal in the patient groups. Full–field log S values (sensitivity parameter), however, were significantly lower than normal (meanr: 1.13 ± 0.12 µV; meanc: 1.68 ± 0.13 µV) for both rods (mean: 0.99 ± 0.1 µV; p < 0.05) and cones (mean: 1.39 ± 0.17 µV; p < 0.01) in the Stargardt group. Central rod amplitude was reduced by 36.3% (mean: 31.9 ± 5.2 µV; p < 0.01) in the Stargardt group and by 22.7% in the AMD group (mean 38.7 ± 15.6 µV; p = 0.12) relative to mean normal (50.1 ± 11.6 µV). The central cone maximum response amplitudes of the Stargardt and AMD groups were reduced, on average, by 32.1% (mean 16.7 ± 7.3 µV; p < 0.05) and 27.2% (mean 17.9 ± 6.6 µV; p < 0.05), respectively when compared to control values (mean 24.6 ± 5.9 µV). Conclusions: Lower than normal full–field log S values in the Stargardt group, as shown previously, suggest abnormal photoreceptor function across the retina. Our results also support previous findings that, in the central retina, both rod and cone photoreceptors are affected in macular degeneration. In Stargardt macular dystrophy, however, there is a tendency for slightly greater loss in rod– than in cone–mediated photoresponses.
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