Geniculate hemianopias: incongruous visual defects from partial involvement of the lateral geniculate nucleus.

Quantitative perimetric studies in 4 patients with involvement of a lateral geniculate nucleus revealed strikingly incongruous defects in the corresponding homonymous fields of vision. The patterns of these hemianopias are analysed and correlated anatomically with established retinotopic projections on the six cellular laminae of the geniculate nucleus. Incongruous wedge-shaped field defects appear to be pathognomonic of focal disease in the dorsal crest of the geniculate nucleus. Other patterns typify lesions of the medical or lateral horns of the nucleus. On theoretical grounds monocular hemianopic defects should result from unilaminar geniculate lesions, but this perimetric sign awaits confirmation. In each case of geniculate disease where the retinal nerve fibre layer has been examined specifically for efidence of retrograde homonymous atrophy, typical hemiretinal signs were found to be present.