The Effects of Afferent Disease on the Timing and Contraction of the Pupil Light Reflex

Abstract

Abstract: : Purpose: Landmarks of the recorded pupil light reflex corresponding to contraction onset, maximum contraction velocity, peak contraction, and maximum dilation velocity may provide a new means for comparing the diagnostic power of pupil contraction and timing during different parts of the light reflex. To compare the diagnostic power of timing and amplitude of the pupil light reflex for detecting abnormal input asymmetry between the two eyes. Methods: 49 normal subjects and 46 patients with asymmetric visual field deficit due to prechiasmal visual pathway damage were tested. A dual–channel infrared pupillograph was used to simultaneously record the right and left pupil diameters during an alternating pulse stimulus over 7 different stimulus intensities. Right–eye responses were linearly correlated to left–eye responses over the 7 intensities at each of the time and amplitude windows for each subject. A logistic regression model was used to compare the ability of the amplitude and timing windows of the pupil light reflex to differentiate normal subjects from patients. Results: Use of the timing landmarks of the pupil light reflex correctly identified normal subjects in 91.8% of cases and patients in 89.1% of cases. Use of the contraction amplitude at the same landmarks for the same pupil light reflexes correctly identified normal subjects in 77.6% of cases and patients in 67.4% of cases. Conclusions: The timing of the pupil light reflex during different parts of the contraction and dilation phase had greater diagnostic power compared to the amplitude of pupil movement, in the group of normal subjects and patients tested. We are currently investigating whether the cause and amount of input asymmetry can differentially affect timing and amplitude of movement.

Keywords: pupillary reflex • pupil • visual impairment: neuro–ophthalmological disease