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DG Birch, DC Hood, KG Locke, DR Hoffman, RT Tzekov; Normal Aging, Progression With Disease, And Test-Retest Variability In Erg Measures Of Cone And Rod Phototransduction . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1770.
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Purpose: To determine normal values for cone and rod phototransduction parameters derived from the a-wave of the electroretinogram (ERG), their dependence on age, the progression in rod parameters in patients with x-linked retinitis pigmentosa (XLRP), and the test-retest variability of these a-wave measures compared to the variability in cone and rod b-wave measures. Methods: ERG responses to high-intensity stimuli were used to elicit rod-only and cone a-waves from 100 normal volunteers (5-75 yrs) and 20 patients with XLRP (5-38 yrs). Rod and cone phototransduction parameters were derived by computer-fitting physiologically-based computational models to the leading edges of a-wave ensembles. Results: Phototransduction efficiency, as indexed by S, decreased with age for both cone and rod-only responses, while maximum cone (cone RmP3) and rod (rod RmP3) photoresponses remained constant. In patients with XLRP followed for four years, rod RmP3 declined with disease progression, while rod S remained stable. The test-retest variability in cone and rod RmP3 is lower than previously-reported measures of the variability in cone- and rod-mediated peak-to-peak amplitudes. Conclusion: The leading edge of the a-wave of the ERG to high-intensity stimuli can be related to rod and cone phototransduction parameters through quantitative models. RmP3, rather than S, should be the outcome measure of choice when using the a-wave to follow photoreceptor function in prospective studies and/or treatment trials for retinal degeneration.
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