Noninvasive assessment of retinal function in rats using multifocal electroretinography

PURPOSE. To assess the applicability of multifocal electroretinograms (mfER Gs) for evaluation of function in this small-el ed animal with a rod-domina nt retina that is often used to model retinal diseases. METHODS. Noninvasive monocular mfERGs were recorded in anesthetized albino (Sprague-Dawley) and pigmented (Long Evans) rats. Achromatic stimuli subten ding a 49 degrees by 53 degrees field consisted of 61 hexagons that were ge nerated and presented (at varying rates and luminances) using a Visual Evok ed Response Imaging System (VERIS; EDI, San Mateo, CA). The VERIS also was used to calculate individual responses and for analysis. RESULTS. mfERGs were recorded from pigmented and albino rats by slowing the rate of stimulus presentation to allow fur the slow recovery time of the r od system. In each mt strain, responses varied systematically with changes in stimulus parameters. Peak response amplitude increased as the rate of st imulation was slowed and as stimulus luminance was increased. Response late ncy decreased as stimulus intensity was increased. The local nature of the response was assessed by several independent measures. CONCLUSIONS. The present work demonstrated the feasibility and limitations of using mfERG to assess topographical changes in the rat retina. It showed that despite the problems of the unavoidable self-adapting nature of the s timulus, the small eye of the animal, and the high potential for light scat ter within the retina, multifocal responses with a good signal-to-noise rat io can be obtained from the rat.