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Vaegan, B. Lowrey, P. Beaumont; The Light Rise of the Photopic Electroretinogram (ERG) in Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2003;44(13):516.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We recorded the light rise of the photopic ERG to resolve differing reports as to whether the light rise of the ERG is affected by retinitis pigmentosa (RP) and whether the size of the light rise is greater in patients with smaller initial ERG amplitudes. Methods: Both eyes of 31 normal people and 59 positively diagnosed RP patients were tested with an ERG protocol which included photopic ERGs to ISCEV standard white flashes and the same flashes on a fully rod saturating (150 cd/M2) background, before and immediately after dark adaptation. We excluded recordings from 14 RP patients with flat traces and, in various conditions, up to 7 more responses, mainly a-waves, which were close to noise (<2.5µV). Results: Ratios of ERG response amplitudes, before and after dark adaptation, for a- and b- waves from both eyes on both backgrounds, varied little. Over all eyes the b-wave averaged 1.88 (s.d. 0.41) for normal people and 1.66 (s.d. 0.62) for RP patients. The a-wave averaged 1.44 (s.d. 0.42) for normal people and 1.31 (s.d. 0.73) for RP patients. All 8 t-tests were insignificant. A loose one tailed error level for multiple comparisons (0.1/ 4, 70 d.f.) was 2.4. There was a positive correlation between the size of the light rise in retinitis pigmentosa and the initial b- wave amplitude but no correlation with initial a- wave amplitude. The a-wave showed a slightly smaller light rise than the b- wave in both groups. Conclusions: The light rise remains normal in RP as long as the photopic ERG is recordable. There is a reduction in RP but it is insignificant relative to normal. These b-wave results are substantially in agreement with a previous study, also based on a large sample, by Yamamoto et al. (2000). The ERG light rise is probably connected to photoreceptor hyperpolarisation but the difference, reported here, between a- and b- waves suggests that post receptoral processes are also involved. Yamamoto, S., Hayashi, M., and Takeuchi, S. Acta Ophthalmol Scand. 2000;78(4):403-6.
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