Objective
The maturation in the central nervous system and the myelination of visual pathway were shown to be reflected by the visual evoked potential (VEP) response recordings. The purpose of this study was to establish normal value of flash visual evoked potentials in preterm infants, especially left to right difference.

Method
Forty-one preterm infants from 31 to 40 weeks of corrected age had been made VEP records using Cadwell Excel EMG/EP system. Some in whom weekly VEP records had been made at least 3 times were included in longitudinal study and others in occasionally VEP records were included in cross-sectional study. Infants with neurological problems or anomalies, perinatal infectious and other severe systemic disease were excluded.

Results
1) In the VEP study, we were able to establish the reference ranges for N300 peak latency at various corrected ages. 2) The latency of N300 peak latency was not significantly correlated with birth weight, sex, head circumference. 3) The latency of N300 peak decrease linearly, the age increased and also the decrement of N300 peak latency was accelerated at 37 weeks of gestational ages.

Conclusion
Although VEPs from preterm infants have several peaks, N300 latency is the most prominent and the most reproducible. It has been considered the most important component of the preterm VEPs.