Contraction Anisocoria caused by Half-Field Stimulation

In 13 normal subjects, we recorded pupillary responses to alternating half-field visual stimuli generated on a video monitor. We found that stimulation of the temporal visual field produced more pupillary constriction than did equivalent stimulation of the nasal field. Stimulation of the temporal visual field also produced a direct pupillary response that was larger than the consensual response. Stimulation of the nasal field, however, caused a larger consensual pupillary response than a direct response. Our findings imply an asymmetric decussation of pupillomotor pathways in the midbrain in humans, as well as greater sensitivity of the nasal retina.