Peripheral prism glasses may benefit patients with hemianopia

Peripheral prism glasses can improve general mobility in patients with hemianopia, according to a multicenter study published in the May issue of Archives of Ophthalmology.

"However, objective measures of functional performance with and without prisms and a control or comparison treatment were not included [in the study]," the authors said. "To provide a more rigorous evaluation of the efficacy of the peripheral prism glasses, we are now conducting a randomized, controlled, multicenter crossover trial using real and sham prisms."

Alex R. Bowers, PhD, and colleagues reported on 15 community-based vision rehabilitation practitioners at 18 clinics across the United States who fit 43 homonymous hemianopia patients with temporary press-on Fresnel peripheral prism segments of 40 prism diopters. These patients all had corrected monocular visual acuity of at least 20/50 in each eye.

To evaluate the prism's functional impact on mobility, the researchers administered questionnaires after 6 weeks of prism wear. Subsequently, patients who continued wearing the prisms were interviewed again by telephone after at least 6 months. Primary outcome measures were clinical success — based on a clinical decision to continue wear — and a five-point rating of prism helpfulness for detecting obstacles on the "blind" side while walking.

Of 43 total patients, 32 patients (74%) had continued prism wear after 6 weeks and 20 patients (47%) had sustained prism wear for a median of 8 hours daily for at least 12 months, the authors noted.

"These participants rated the prism glasses as very helpful for obstacle avoidance and reported significant benefits for obstacle avoidance in a variety of mobility situations," they said.

Success rates varied among clinic groups, with higher rates reported at clinics that fitted eight or more patients (81%) than at clinics that fitted five or fewer patients (27%), according to the study.