Hemianopic Fresnel prisms.

Patients with homonymous hemianopic visual field defects have been treated by using a 30-diopter Fresnel plastic paste-on prism on their glasses. A patient with a left homonymous hemianopia, for instance, can have a 30-diopter base left (i.e., base out) Fresnel prism placed on the temporal half of the left spectacle lens. The prism need be only on one lens. A small 1- to 1.5-mm portion can be cut out of the center to prevent diplopia. This device is widely available and easier to obtain than a hemianopic mirror on the frames. Use of this device is illustrated in the report.