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A.M. Binns, T.H. Margrain; The ERG Photostress Test . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1899.
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Purpose: To develop an objective, electroretinographic test capable of evaluating the recovery of macular function following exposure to bright light, and to assess the repeatability of the technique in healthy adults. Method: Ten adult young volunteers participated in the study. Following pupil dilation, a steady-state base-line electroretinogram (ERG) was elicited by exposing the eye to a circular amber (595nm) stimulus, with a time-averaged mean luminance of 30 cd.m-2, flickering at 41 Hz. The stimulus, which subtended 20°, was surrounded by a luminance-matched annular white surround designed to suppress responses from the peripheral retina. Responses from a DTL fibre electrode and reference electrode placed at the outer canthus were amplified, averaged and band-pass filtered using a Medelec Synergy system (filtered 1-100 Hz, 100 sweeps averaged). Subsequently the eye was light-adapted to a bright white background (5.6 log photopic trolands) for 2 minutes, and the recovery of the 41 Hz focal cone ERG was monitored for a period of 4 minutes. The resulting data was modelled using a single exponential function. Results: In all cases there was no recordable ERG immediately after the bleach and baseline ERG amplitudes returned within 4 minutes. Determination of the coefficient of repeatability (of the recovery time constant) indicates that the ERG photostress test is likely to be a viable clinical tool. Conclusion: The focal 41 Hz ERG is a quick and efficient method of obtaining objective information on the functional integrity of cone photoreceptors in the macular region. As such, it is an ideal technique for monitoring retinal recovery following a period of intense light adaptation. The ERG photostress test may be useful in the early detection of age-related macular degeneration, a disease that has previously been shown to affect the kinetics of the dark adaptation function. The long-wavelength stimulus should be relatively unaffected by age-related media changes, and thus suitable for use on older adults.
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