[Fresnel prisms--their value in the rehabilitation of homonymous hemianopsias].

The use of press-on Fresnel prisms is described as a simple inexpensive technique to rehabilitate patients with homonymous hemianopsia. The optical principle of prismatic displacement from the blind to the seeing fields is detailed herein. Forty-one patients were evaluated over a 10 year period. Twenty per cent benefited from the prism. Many of those who found limited or little value from their use expressed appreciation that something had been tried in order to improve visual function. Those patients with good acuity and an otherwise normal neurological status are the best candidates. Proper motivation and instruction are essential.