Influence of cataract on the multifocal ERG recording--a pre- and postoperative comparison

To study the influence of cataract on the multifocal electroretinogram (mfERG), 18 patients underwent mfERG recordings prior to and following cataract surgery. The central 50 degrees of the retina were stimulated by 103 hexagons alternating independently between white and black according to a binary m-sequence. The frame rate was 75 Hz. The maximum luminance was 200 cd/m2, the minimum luminance < 1 cd/m2 with a mean luminance of 100 cd/m2. For each retinal location, the latencies of the first negative peak (N1), the first positive peak (P1) and the second negative peak (N2) as well as the amplitude from N1 to P1 and the amplitude from P1 to N2 of the first order response were obtained. Concentric ring averages around the foveal response were analyzed. Following cataract surgery, the mean amplitude of the response in the central four degrees increased from 37.83 to 42.37 for N1P1 (p = 0.019) and from 39.44 to 47.20 for P1N2 (p = 0.001). To reduce the influence of retest variability, each response average was divided by the recording's overall amplitude. For the central 4 degrees this ratio increased by 0.18 (p = 0.002) for N1P1 and by 0.27 (p < 0.001) for P1N2. Clouding of the optic media such as produced by cataracts has a slight but significant influence on the multifocal ERG.