Pupil constriction and visual evoked potential latency in optic neuritis

Prolongation of both pupil and visual evoked potential (VEP) latencies was demonstrated in a group of 49 optic neuritis patients. Pupil constriction latency was determined using a technique which allowed simultaneous measurement of the direct and consensual light reflex. Both eyes were stimulated separately. In this way pupillometry allowed a differentiation between efferent and afferent defects, while with the VEP only afferent defects can be demonstrated. Because of the first parallel trajectories of both evocations, afferent pupil and VEP abnormalities were compared; however, no significant correlation was found. This discrepancy was canceled when involving the recovering time after the acute stage of the optic neuritis. It turned out that the pupil latency remained abnormally prolonged after the acute stage, while the VEP latency returned to its baseline value