We use the Visual Evoked Potential (VEP) to see whether there is a lesion on the visual pathway or not, normally with two kinds of stimulation of flash (goggle) and pattern-reversal (checkerboard) stimulation.

The purpose of this study is to establish the normal value of latencies in above-mentioned two kinds of VEP and compare the efficiency in clinical use between them, and see the correlation of sex, age and the length of visual pathway to the latencies of representative waves (N2 in flash stimulation and P1 in pattern-reversal stimulation) of each method.

42 volunteers (27 females and 15 males) without visual problem were studied with both methods and the mean age of subjects was 33.6 years old.

The results were as follows:

1) The waves in flash stimulation were composed of 5 waves of N1, P1, N2, P2, and N3 the incidence of N2 was highest with 95%. The waves in pattern-reversal stimulation (PRS) were composed of 3 waves of N1, P1 and N2 and the incidence of P1 and N2 were 100%. The mean value of latency of N1, P1, N2, P2 and N3 by flash stimulation was 59.5±7.4 msec, 75.4±7.6 msec, 91.7±6.9 msec, 109.7±5.9 msec, and 126.4±12.7 msec respectively and that of N1, P1, N2 by PRS was 63.6±3.7 msec, 82.9±3.8 msec, and 103.9±4.2 msec respectively. The range of normal value of N2 in flash stimulation was more wide than that of P1 in PRS, so the P1 in PRS was more valuable diagnostically.

2) The correlation of age to the latencies by each method revealed no statistical significance. But the N2 latency by flash stimulation was inversely correlated with the age and the equation was as follows; N2 Latency (msec)=99.1-0.22xAge (Year)

3) The distances between nasion and inion were much shorter in female than male subject. The P1 latency by PRS was highly correlated with the nasion-inion distance and the equation was as follows; P1 Latency (msec)=42.63+2.21xdistance (cm).

4) The latencies of N1, P1, N2, P2, and N3 by flash and N1, P1, N2 by PRS showed relatively shorter latencies in female compared to that of male.

5) There was no significant difference in latencies between both eyes.