Decline in ERG Maximum a-wave and b-wave Amplitudes with Age

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Growth in the population over age 60 has increased the clinical importance of diseases of the retina associated with aging. The electroretinogram (ERG), long used as a test of retinal function, has potential for providing important clinical insight for retinal diseases of aging patients. However, interpretation of the ERG is complicated by the well documented, but less well understood, decline in response amplitude as a function of increasing age. Insight into factors leading to ERG amplitude decline with age may be provided by study of receptoral changes, reflected in the a-wave component, compared to changes in inner retinal function, reflected in the b-wave component (Pearlman, 1983). Breton et al (1994) and others (Hood and Birch, 1994) have developed a method of ERG a-wave analysis that yields parameters interpretable in terms of total rod dark current (amax), a constant of transduction amplification (A), and a brief delay associated with cascade molecular interactions (t'eff). This analysis is based on a quantitative model of the G-protein mediated phototransduction cascade proposed by Lamb and Pugh (1992). For purposes of this study, an important feature of the Breton et al (1994) procedure and analysis is the recording of rod response at high stimulus intensities where saturated a-wave and b-wave component amplitudes (amax and bmax) can be effectively measured with minimal algebraic interference with one another (Breton and Montzka, 1992). Based on this approach, changes in ERG amplitudes during development and aging can be used to infer changes in underlying retinal mechanisms. We use this approach to measure maximum a-wave and b-wave amplitudes and receptor transduction response as a function of age in human infants, toddlers and adults from several days up to 80 years.