Communications

Abstract

It is generally accepted that both pupils constrict equally when one eye is illuminated and that any inequality in the direct and consensual responses to light indicates a lesion in the light reflex pathways (Lowenstein & Loewenfeld, 1969). In this presentation, evidence that light reflex inequality is common in normal subjects will be described.Anisocoria in darkness and following unilateral light stimulation was measured in 150 normal subjects (mean age 34*9 yr; range 18-67 yr) by television pupillometry, a technique demonstrated to the Society. In 85 % of subjects the direct light reaction of the illuminated eye was found to exceed the consensual reaction of the other eye by a small but significant extent. This light-induced anisocoria, termed 'contraction anisocoria', had a mean value of 0 075 mm or 6 1 % of light reflex amplitude. The measurement showed a high degree of repeatability (intrapair correlation coefficient r = 0.82) when 20 subjects were retested a year later. The measurement of resting pupillary anisocoria in darkness was less repeatable (r = 0.56).The extent of contraction anisocoria was uninfluenced by dark-adaptation of the subjects prior to testing. It was found to increase proportionally with reflex amplitude as the intensity of the stimulating light was raised, so that contraction anisocoria expressed as a percentage of reflex size was not influenced by the brightness of the light.In these experiments the position of the stimulating light was such that there was probably a predominant illumination of the nasal retina. Experiments are in progress to determine whether discrete illumination of the temporal retina results in a similar degree of contraction anisocoria. The basis of the physiological occurrence of a small degree of light-induced anisocoria was discussed.