Aim To study the characteristics of pupillary responses in patients with homonymous hemianopia following acquired post-geniculate lesion.

Methods Eighteen individuals were recruited and were divided into two groups:

(1) Eleven patients with acquired homonymous hemianopia following occipital lobe and/or optic radiation damage and

(2) Seven control subjects who had normal vision. P SCAN 100 system was employed to generate visual stimuli and to measure the pupil responses in each eye. There were two types of stimulus, chromatic and achromatic. The stimuli were presented randomly in either sighted or blind hemifield in the patient group; and right or left hemifield in the control group and the patients viewed a fixation point on a display binocularly. The latency, amplitude, and post-stimulus dilatation of the pupil light refles (PLR) were measured.

Results There was no difference in PLR latency between the blind and sighted hemifields in the patient group. PLR amplitude following stimulus presentation in the blind hemifield was small or absent compared to the results obtained in the sighted hemifield and in the control subjects. PLR dialtation in the blind hemifield was slower than the sighted hemifields while there was no significant dilatation difference between right and left hemifields in the control subjects. This was suggestive of hemipupillary dilatation lag contralateral to the lesion, a sign of sympathetic dysfunction.

Conclusion Damage to the occipital lobe affects both the constriction and the dilatation phases of the PLR.