Variability on serial testing of pattern reversal visual evoked potential latencies from full-field, half-field and foveal stimulation in control subjects.

The change in pattern reversal visual evoked potential (PRVEP) latency over time (test-retest variability, TRV) was assessed in 30 (16 males, 14 females) adult control subjects using full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation. The mean test-retest interval (TRI) was 20.5 months with a range of 18-21.5 months. There were no significant test-retest latency differences in either sex and furthermore there were no significant inter-sex differences in any of the test-retest parameters. Because of the latter finding the test-retest upper limit of normal for each parameter as defined by the mean value + 2.5 S.D. was taken as the largest value obtained in either sex. Thus the test-retest upper limits of normal for absolute latency from FF, right HF, left HF and CF stimulation were 6, 7, 9 and 7 msec, respectively; for interocular latency differences (ILD) from FF and CF stimulation were 4 and 5 msec respectively; and for right HF to left HF intraocular latency difference (IOLD) was 7 msec. It is concluded that the TRV was sufficiently small in our control group with each of the stimulus techniques to make all of them potentially useful in serial PRVEP studies. Furthermore the extra information provided by CF and HF stimulation may increase the sensitivity and accuracy with which change can be monitored.