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S Grover, GA Fishman, DG Birch, KG Locke, B Rosner; Variability Of Full-field Erg In A Population Without Diffuse Photoreceptor Cell Disease . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1166.
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Purpose:The full-field ERG is a useful tool for diagnosis in patients with hereditary and acquired retinal diseases. Moreover, it is also of value in monitoring retinal function during therapeutic trials in such patients. For each ERG response, it is important to determine the threshold for a significant increase or decrease during a longitudinal study. Limited information is available for patients with hereditary retinal disease; here we evaluate test-retest variability in ERG responses in subjects without diffuse photoreceptor cell disease. Methods: ERG data were collected prospectively from 40 subjects who participated in a study by a pharmaceutical company investigating the effects of certain gastrointestinal drugs on retinal function. None of the subjects were on any drug shown to affect the ERG. A mean of six ERG’s (range, 3-13) were obtained on each subject over a period of 2 - 6 years. The ERG responses evaluated included amplitudes and implicit times for the dark-adapted rod-isolated and rod-dominant responses, light-adapted single flash response and both light- and dark-adapted 31Hz flicker responses. The data were analyzed by using analysis of variance methods. A threshold criteria for significant change (with 95% confidence) was calculated for implicit times and an increase and decrease in ERG amplitudes. Results:For the implicit times, the threshold for significant change varied from 3 - 8.7 ms, depending on the stimulus. For the dark-adapted stimuli, a significant decrease in amplitude varied from 35% - 42% whereas a significant increase varied from 53% - 73%. For the light-adapted stimuli, variations for a significant decrease and increase were 52% and 109% - 110%, respectively. Amplitudes for the dark-adapted rod-dominant responses were significantly less variable than for the single flash light-adapted responses (p<.001). Conclusion:The ERG test-retest variability observed in these subjects without diffuse retinal disease should be compared to similar comprehensive studies of test-retest variability in patients with various hereditary and acquired retinal diseases. Such data are of value in monitoring disease progression and in future therapeutic trials in such patients.
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