The fetal visual evoked potential.

Five singleton fetal lambs were surgically instrumented at 110-121 days gestation (term gestation = 145 days) for measurement of visual evoked potentials (VEP) in utero. Light flashes were generated by a small incandescent bulb secured under the right fetal eyelids and the visual responses were recorded through stainless steel electrodes implanted in the fetal scalp. Four of the five fetal lambs were surgically instrumented between 110-113 days. VEPs recorded in these four animals from 111-114 days exhibited N1, P1, and N2, but lacked the P2 component. All VEP components (N1, P1, N2, P2) were measureable by 115-118 days in these fetuses. One fetus was surgically instrumented at 121 days and VEPs containing all components were measurable until 125 days gestation when the equipment dislodged in utero. Serial VEP recordings from all five fetal lambs from 111-128 days indicated no change in latency to N1 while significant latency changes occurred in P1, N2, and P2 suggesting maturational development of the visual system. Histological assessment of the eyes from three animals at delivery revealed only thickening and increased vascularity of the cornea in response to the light source resting on the fetal eye. In conclusion, these results suggest that the fetal visual evoked potential has application in the longitudinal study of normal visual development in utero and offers a technique for studying visual response changes to adverse perinatal events.