CLINICAL-EVALUATION OF VEPS TO INTERLEAVED CHECKERBOARD REVERSAL STIMULATION OF CENTRAL, HEMIPHERAL AND PERIPHERAL FIELDS

The VEPs of 195 patients referred for supportive evidence of multiple sclerosis or optic neuritis were studied by a new method of interleave d checkerboard reversal stimulation of different areas of the visual f ield. In the first group of 95 patients checks of 40' subtense reverse d in the whole field (28 degrees X 20 degrees), alternately in the lef t and right hemifields and alternately in the central (5 degrees radiu s) and peripheral fields. In the second group of 100 patients checks r eversed in the whole field and in interleaved mode in 3 visual field a reas, comprising the central (4 degrees radius) and left and right hem isurround fields. In the first group abnormal responses were recorded from 52 eyes and there was partial disagreement among the stimulus con ditions in 10 of the 52. Abnormalities were seen uniquely to central f ield stimulation in 3 eyes but never to whole field stimulation alone. In the second group abnormal responses were recorded in 58 eyes, agai n never uniquely to whole field stimulation, while abnormalities confi ned to one or two areas of the visual field were seen in 24, providing evidence of peripheral field involvement alone in 8 eyes. In the firs t group, waveforms created from the sum of the left and right hemifiel d and central and peripheral field responses showed quite close confor mity to the whole field VEP, although amplitudes were significantly lo wer and latencies significantly shorter. In 7 eyes responses would hav e been differently classified (normal or abnormal) using the sum as co mpared with the whole fields. The sum of the 3 interleaved stimuli was less reliable, its morphology often not closely approximating whole f ield responses. It is suggested that interleaved stimulation of two or more areas of the visual field is a sensitive and reliable method whi ch reduces the time necessary to perform the test and helps control th e patients' concentration, fixation and alertness. Whole field stimula tion is probably necessary only in patients with severely degraded res ponses.