IMPLICIT TIME TOPOGRAPHY OF MULTIFOCAL ELECTRORETINOGRAMS

PURPOSE. TO describe the implicit time topography of multifocal electr oretinograms in normal subjects and to examine the change in this topo graphy in patients affected by retinitis pigmentosa. METHODS. Thirty n ormal subjects and 38 patients with retinitis pigmentosa were examined with the Visual Evoked Response Imaging System using 61 hexagonal ele ments within a visual field of 30 degrees radius. The peak implicit ti mes of the 61 first-order kernels (which are analogues of the photopic electroretinogram [ERG]) were measured to determine their distributio n across the retina. RESULTS. Implicit times had a low interindividual variability in the normal group. High implicit times were found at th e blind spot. the upper and lower borders of the stimulated field, and the macula. Loof values were present in the area encircling the macul a and were most prominent in the temporal retina. In the group with re tinitis pigmentosa, implicit times were unchanged in the central regio n but were prolonged in the peripheral regions. CONCLUSIONS. The spati al distribution of multifocal ERG implicit times in a normal populatio n follows a specific topographical pattern across the retina. This pat tern has to be taken into account when interpreting results in patient s. Deviations in retinitis pigmentosa were found, and they show the po tential for diagnostic use.