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P. Kozma-Wiebe, K.G. Locke, D.H. Wheaton, D.C. Hood, D.G. Birch; The Relationship Between ERG Measures of Phototransduction Efficiency and Genotype in Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1863.
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Purpose: Photoreceptor activity in humans can be studied by analyzing the a-wave of the electroretinogram (ERG) recorded to high intensity lights. Our aim was to determine the degree to which abnormalities in phototransduction parameters are associated with specific disease-causing mutations. Methods: Dark- and light-adapted ERG a-wave responses to white flashes were recorded in patients with widespread retinal degeneration associated with RPGR (n=7), CRX (n=6), RP1 (n=4), RDS/Peripherin (n=34), Rhodopsin (RHO) (n=28) and ABCR (n=12) mutations. Rod and cone transduction efficiency (S) in each patient was compared to normal values based on 100 normal subjects (Birch et al, 2002). S was measured by the method described by Hood and Birch (1997). Four high flash intensities, ranging from approximately 3.2 to 4.4 log scot td-s, were presented first to the dark adapted eye and then on a rod-saturating background (3.2 log td). Rod-only responses were derived by the subtraction of light-adapted responses from the dark-adapted ones. Results: Rod S values were lower than the lower limit of normal for most patients with RHO (mean ΔS:-0.36) and ABCR (mean ΔS:-0.41) mutations but were within normal limits for other mutations. In the RHO group, patients with Pro23His mutation had low rod S values (mean ΔS:-0.49) whereas patients with other RHO mutations had values within, or close to, the normal range. Rod S values did not vary systematically with age. Cone S values were below the lower limit of normal in all mutations with the exception of RDS/Peripherin. In general, cone S values were more variable and lower after age 40. Conclusions: The decreased rod photosensitivity in many patients with RHO mutations is consistent with an abnormality that affects the activation of phototransduction. The normal or close to normal rod S values in other mutations indicates that they do not play a role in the activation process. The diminished cone S values in all patients except those with RDS/Peripherin mutations are presumably secondary effects since the mutations studied here primarily affect rods. These results suggest that ERG measures may be helpful for identifying patients likely to have mutations influencing the sensitivity of phototransduction.
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