To evaluate the value of congruency in the localization of brain lesions in patients with homonymous hemianopia (HH).

Retrospective observational study.

Charts of all patients with HH seen over 15 years were reviewed. Only patients with incomplete HH documented on formal visual field testing and neuroimaging were included. HH was said to be congruent when the fields of both eyes were identical in shape, depth, and size. Patients were divided into two groups based on congruency of HH; demographic, clinical, and radiological characteristics were compared.

Five hundred and thirty patients with 548 incomplete HH were included (373 congruent HH and 175 incongruent HH). Demographic variables were similar in both groups. Stroke caused 75% of congruent HH and 55.8% of incongruent HH; trauma and tumors caused 20.5% of congruent HH and 34.5% of incongruent HH (P < .001). The lesion locations in congruent HH vs incongruent HH included occipital lobe in 47.9% vs 21.3%, occipital lobe and optic radiations in 8.3% vs 5.6%, optic radiations in 32.4% vs 50.6%, optic tract in 7.2% vs 16.3%, and other locations in 4.2% vs 6.3% (P < .0001). Although there was a trend toward more congruent HH for lesions of the posterior visual pathways (P < .001), 50% of optic tract lesions and 59% of optic radiation lesions produced congruent HH.

Although lesions involving the occipital lobe characteristically produce congruent HH, at least 50% of lesions in other locations also produce congruent HH, especially if these lesions are stroke-related. The rule of congruency should be used cautiously and may not apply to optic tract lesions.