Noninvasive assessment of retinal function in rats using multifocal electroretinography

To assess the applicability of multifocal electroretinograms (mfERGs) for evaluation of function in this small-eyed animal with a rod-dominant retina that is often used to model retinal diseases.

Noninvasive monocular mfERGs were recorded in anesthetized albino (Sprague-Dawley) and pigmented (Long Evans) rats. Achromatic stimuli subtending a 49 degrees by 53 degrees field consisted of 61 hexagons that were generated and presented (at varying rates and luminances) using a Visual Evoked Response Imaging System (VERIS; EDI, San Mateo, CA). The VERIS also was used to calculate individual responses and for analysis.

mfERGs were recorded from pigmented and albino rats by slowing the rate of stimulus presentation to allow for the slow recovery time of the rod system. In each rat strain, responses varied systematically with changes in stimulus parameters. Peak response amplitude increased as the rate of stimulation was slowed and as stimulus luminance was increased. Response latency decreased as stimulus intensity was increased. The local nature of the response was assessed by several independent measures.

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 stimulus, the small eye of the animal, and the high potential for light scatter within the retina, multifocal responses with a good signal-to-noise ratio can be obtained from the rat.