The Marcus Gunn pupil in incomplete optic tract hemianopias.

Three patients with optic tract lesions, incomplete homonymous hemianopias, and good vision in both eyes are presented. All three had a Marcus Gunn pupil in the eye with temporal field loss (eye contralateral to the tract lesion). This pupillary sign may serve to differentiate acute optic tract from acute geniculostriate lesions when the characteristic infrageniculate optic atrophy has not had time to develop.