ELSEVIER Ophthal. Physiol. Opt. Vol. 17, No. 1, pp. 25-31, 1997 Copyright 0 1996 The College of Optometrists. Published by Elsevier Science Ltd Printed in Great Britain 0275.5408/97 $17.00 + 0.00 PHI: SO2755408(96)00046-4 Variation of topographic visually evoked potentials across the visual field Min-Zhong Yu and Brian Brown Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hung Horn, Hong Kong Summary We examined the variation of monocular pattern reversal topographic visually evoked potentials across a 13.6O visual field and measured the parameters of the VEP waveforms in 37 locations across the field. Eighteen right and 20 left normal eyes were tested from 23 subjects. The mean response densities of the VEP decreased with increasing eccentricity; response densi- ties are higher in the lower hemifield than in the corresponding mirror symmetric locations in the upper hemifield. The incidence of polarity reversal is higher in the upper hemifield, especially in more superior locations. The latency in the temporal field is shorter than that in the other locations. The coefficients of variations (CVs) of latencies are less than those of amplitudes in corresponding locations and the CVs of latencies of PI and N2 components are less than those of the Nl component in corresponding locations. The CVs of amplitudes of the waveforms in mid-peripheral locations are larger than those of the other central areas. The parameters of the human topographic visually evoked potential are distributed regularly across the visual field and appear to reflect the underlying anatomy of the retina and visual cortex, and the placement of the recording electrode. Copyright 0 1996 The College of Optometrists. Published by Elsevier Science Ltd. Introduction The ,visually evoked potential (VEP) is frequently used to obtain insight into the organization of the visual system in man, as well as being used as a diagnostic tool in the clinic. In the study of the VEP in man, most investigators have elicited the visual response by using a checkerboard pattern of variable check size, typically as large as 20” on a side. This type of stimulation simultaneously involves both central and peripheral vision. Although it is the most con- venient way to test the VEP it can only reflect the summed responses over the visual field. In order to reveal local visual function within the visual field, some authors (Hennerici et al., 1977; Rossini et al., 1979) have suggested that smaller stimulus fields should be used. Half fields (Jeffreys and Smith, 1979; Lesevre, 1982; Skrandies and Lehmann, 1982), quadrants (Lesevre and Joseph, 1979; Darcey et al., 1980; Ossenblock and Spekreijse, 1991), octants (Halliday and Michael, 1970; Butler et al., 1987), half annuli (Maier et al., 1987), Received: 16 February 1996 Revised form: 17 June 1996 central/peripheral fields (Cohn and Hurley, 1985) and small fields (Celesia and Meredith, 1982; Tyler and Apkarian, 1982) have been used to test local visually evoked responses. However, the sequential method of stimulus presentation limits the practical number of stimulus locations that can be tested. Most of the studies employing small stimuli men- tioned above have been confined to dividing the tested field into a small number of parts and they were not detailed enough to reveal the local variation of the VEP. In recent years, pseudo-random visual stimulation has been applied in measurements of both the electroretinogram (Sutter and Vaegan, 1990; Sutter and Tran, 1992) and the visually evoked potential (Srebro and Wright, 1982; Baseler et al., 1994). This technique permits a much more complete description of the local VEP characteristics than is possible with conventional methods. Some characteristics of the binocular topographic VEP across the visual field have been explored in a few normal subjects using this technique (Baseler et al., 1994). We have used this tech- nique and quantitatively measured the parameters of the monocular topographic VEP; 37 VEP traces over the visual field were measured for 38 normal eyes. Variation of response density and latency of three VEP peaks, Nl, PI 25