Determining abnormal interocular latencies of multifocal visual evoked potentials Donald C. Hood 1 , Xian Zhang 1 , Christopher Rodarte 1 , E. Bo Yang 1 , Nitin Ohri 1 , Brad Fortune 2 & Chris A. Johnson 2 1 Department of Psychology, Columbia University, New York, NY USA; 2 Discoveries in Sight, Devers Eye Institute, Legacy Health System, Portland, OR, USA Accepted 25 October 2004 Key words: electrophysiology, latency, multifocal visual evoked potential, VEP Abstract Purpose: To describe methods for measuring interocular latency differences of multifocal visual evoked potentials (mfVEP) and for determining regions with abnormal interocular latencies in patients. Methods: The mfVEPs from 100 individuals with normal visual fields and normal fundus examinations were analyzed. Individuals ranged in age from 21.6 to 92.4 years. The stimulus was a 60 sector, pattern- reversing dartboard display. Each sector had 16 checks, 8 white (200 cd/m 2 ) and 8 black (<1 cd/m 2 ). In- terocular latency was measured as the temporal shift producing the best cross-correlation value between the corresponding responses of each eye. The ‘corrected interocular latency’ was defined as the difference between this shift and the mean interocular latency (shift) for a particular sector and recording channel. Results: The variability of the corrected interocular latency decreased as the signal-to-noise ratio (SNR) of the mfVEP responses increased. For example, the 95% confidence intervals decreased from over 16 ms to under 4 ms as SNR increased. Grouping and summing the responses also lead to an increase in SNR and a decrease in the confidence interval. The results of various cluster criteria were also derived. A cluster criterion (e.g. two or more contiguous points within a hemisphere exceeding a given confidence interval), can serve to increase the specificity for detection of eyes or individuals with abnor- mal interocular latencies. For example, while 21% of the eyes had 3 or more points exceeding the 5% confidence interval, only 1.8% of the eyes had a cluster of 3 or more of these points. Finally, interocular latency was only weakly correlated with age (r ¼ 0.26). Conclusion: In testing for abnormalities in inter- ocular latencies, the confidence interval should be based upon the SNR of the response. Grouping and summing responses to increase SNR or employing a cluster test may also prove useful. Introduction Various diseases of the retinal ganglion cells or optic nerve cause spatially localized losses in visual function. The multifocal visual evoked potential (mfVEP), a technique that allows the recording of scores of local VEP responses [1], provides a measure of these local losses. For example, local losses in amplitude of the mfVEP have been demonstrated in optic neuritis/multiple sclerosis [2, 3] and glaucoma (e.g. [4–14]). While the techniques for analyzing the amplitude of the mfVEP have been described in detail (e.g. [12, 15]), relatively little has been published on how to measure latency. Because disease can affect the latency as well as the amplitude of the VEP (e.g see [16, 17] for a review), it is important to measure both. Here we consider a technique for measuring local differences in interocular latency of the mfVEP and determining whether these dif- ferences are abnormal. While essentially nothing has been published on techniques for measuring monocular latencies of mfVEP records, two studies [18, 19] have Documenta Ophthalmologica (2004) 109:177–187 Ó Springer 2005