The afferent arc of the pupillary light reflex is known to coincide with the afferent visual system from the retinal ganglion cell as far as the optic tract. Thus, asymmetric visual field loss resulting from a lesion here is accompanied by a relative afferent pupillary defect. Patients with total optic tract lesions, for example, show complete homonymous hemianopia and a relative afferent pupillary defect, both contralateral to the involved tract.1 Before axons synapse in the lateral geniculate nucleus, pupillary fibers diverge via the brachium of the superior colliculus to synapse in the pretectal nuclei. These are situated at the level of the posterior commissure just rostral to the superior colliculus.
One would expect, therefore, that unilateral damage to the brachium of the superior colliculus would produce a contralateral relative afferent pupillary defect while sparing visual function. We describe a patient with these findings after a thalamic-dorsal midbrain hemorrhage from
Forman S, Behrens MM, Odel JG, Spector RT, Hilal S. Relative Afferent Pupillary Defect With Normal Visual Function. Arch Ophthalmol. 1990;108(8):1074-1075. doi:10.1001/archopht.1990.01070100030017