Objective: To establish normal values of P100 and P2 latency of visual evoked potentials [VEPs] among Thai adults.

Materials and Methods: A cross-sectional study was conducted among Thai adults without visual abnormalities. The VEPs of participants were tested for both eyes. P100 latency was stimulated from pattern-reversal VEPs whereas P2 latency was stimulated from flash goggled VEPs. The 99th percentile was used as the upper limit of normal.

Results: Among 106 participants (212 eyes), the majority were females (68.9%) with a mean age of 32.1 (10.8) years ranging from 20 to 59 years. The 99th percentile of P100 latency and its interocular latency difference were 119.3 milliseconds and 10.1 milliseconds, respectively. The 99^th percentile of P2 latency and its interocular latency difference were 144.3 milliseconds and 17.1 milliseconds, respectively.

Conclusion: The P100 latency exceeding 119.3 milliseconds or interocular P100 latency difference greater than 10.1 milliseconds should be considered as abnormal results. Because of substantial interpersonal variability of flash VEPs, the upper limit of normal of P2 should not be established. However, interocular P2 latency difference greater than 17.1 milliseconds might be considered as abnormality in the eye with longer latency.

Keywords: Visual evoked potential, Normal values, P100 latency, P2 latency, Interocular latency difference