Community-based trial of a peripheral prism visual field expansion device for hemianopia.

OBJECTIVE To determine the functional utility for general mobility of peripheral prism glasses, a novel visual field expansion device for hemianopia, in a large-scale, community-based, multicenter study with long-term follow-up. METHODS Forty-three participants with homonymous hemianopia were fitted with temporary press-on Fresnel peripheral prism segments of 40 prism diopters. Follow-up questionnaires evaluating functional benefits for mobility were administered in the office at week 6. Participants who continued wearing the prisms were interviewed again by telephone after a median of 12 months. Primary outcome measures included clinical success (a clinical decision to continue wear) and 5-point ratings of prism helpfulness for obstacle avoidance when walking. RESULTS Thirty-two participants (74%) continued prism wear at week 6, and 20 (47%) were still wearing the prisms after 12 months (median time, 8 hours per day). 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. Success rates varied among clinic groups (27%-81%), with higher rates at the clinics that fitted more patients. CONCLUSION Our results demonstrate the functional utility of peripheral prism glasses as a general mobility aid for patients with hemianopia.