Pupillary light reflex latency in patients with multiple sclerosis.

In 46 patients with definite multiple sclerosis (MS) the direct and indirect pupillary light reflex latency (PLRL) and visual evoked potential (VEP) latency of the P100 were measured for each eye separately. The PLRL was measured at both photopic and scotopic illuminance level, using an infrared light reflection technique (IRIS). On average the PLRL increased at the scotopic illuminance level as compared with the photopic (P less than 0.0001). An abnormal VEP was found in 80.4% of the patients, while 26.1% and 29.7% had an abnormal direct PLRL at photopic and scotopic illuminance level respectively. No correlations were found between PLRL and VEP or visual acuity. In MS patients with unilateral optic signs (optic neuritis or slowly progressive visual failure) a relative prolonged PLRL could be demonstrated in the symptomatic eye as compared to the asymptomatic eye. Based on formulae to quantitate relative afferent and efferent impairments of the pupillary pathway, it is demonstrated that prolonged PLRL measurements mainly reflect the nerve conduction in the efferent pupillary pathway.