Relative afferent pupillary defects in patients with geniculate and retrogeniculate lesions

Abstract

We reviewed the clinical findings and imaging studies of 43 patients with homonymous hemianopia and normal optic discs to discover differences between those with and those without relative afferent pupillary defect (RAPD). Methods: RAPD was determined by means of the swinging flashlight test. Visual field defects had to be congruous and no visual loss attributable to retinal or optic nerve disease or other causes of RAPD such as amblyopia was accepted. The imaging studies were reviewed by a neuroradiologist unaware of the clinical findings. Patients with lesions involving the optic tract were excluded. The shape of the lesion was transferred onto standard diagrams of the cerebral imaging sections and the proximity to the lateral geniculate nucleus (LGN) was determined. Results: Sixteen of 43 patients showed RAPD contralateral to the lesion. In these 16 patients, the median distance between the lesion and the LGN was 4.5 mm (maximum distance 18 mm, 14 lesions being closer than 10 mm). In 27 patients without RAPD, the median distance was 15 mm (maximum 45 mm, in 11 patients the distance was shorter than 10 mm). Conclusions: RAPD in homonymous hemianopia is not limited to tract lesions. It occurs in approximately one half of all patients with lesions closer than 10 mm to the LGN or involving it but sparing the optic tract. It does not occur in lesions farther than 18 mm from the LGN. This RAPD is probably not caused by a lesion of the visual pathways itself, but by a lesion of intercalated neurons between the visual pathways and the pupillomotor centers in the pretectal area of the midbrain.

Key Words:

• Pupil
• perimetry
• homonymous hemianopia
• lateral geniculate nucleus
• optic tract
• postchiasmal visual pathways