A randomized crossover clinical trial of multi-periscopic and Fresnel peripheral prism glasses for hemianopia.

PURPOSE To compare novel multi-periscopic prisms (MPP; 42° field expansion) to commercial Fresnel peripheral prisms (FPP; 30° field expansion) as mobility devices to assist with pedestrian collision hazard detection when walking.

METHODS Participants with hemianopia without neglect or cognitive decline were recruited at 7 sites in a single-masked crossover trial, allocated by minimization to receive either MPP or FPP first. Pedestrian collision detection was evaluated after 4-weeks of home-use of each type of prisms. The test simulated walking through a busy shopping mall with multiple pedestrians; in each trial, one pedestrian could be on a collision course, bearing angle of ±20° or ±40°, or there could be no colliding pedestrian. The main outcome, improvement with prisms (yes/no), was defined as blind-side detection rates that were significantly higher with than without prisms at the same visit.

RESULTS Of 64 participants screened, 38 were eligible and 63% (24/38) showed improvement with at least one type of prism glasses. There were no differences between the proportions of participants showing improvement with MPPs and FPPs for either 40° blind-side pedestrians (MPPs 31%, 12/38 vs. FPPs 26%, 10/38; difference 5%; 95% CI -14% to 24%, p = 0.75) or 20° blind-side pedestrians (MPPs 37%, 14/38 vs. FPPs 42%, 16/38; difference -5%; 95% CI -24% to 14%, p = 0.75). Of the 32 participants who completed both crossover periods, 13 (41%) preferred MPPs whereas 19 (59%) preferred FPPs (p = 0.38). MPPs were preferred for image clarity and extent of field expansion and FPPs for cosmetic appearance. Both MPPs and FPPs reduced (p < 0.01) perceived difficulty when walking in unfamiliar areas, crowded situations, detecting objects and people on the blind side, the most difficult situations without prisms.

CONCLUSIONS Both MPPs and FPPs improved blind-side collision detection at large (40°) as well as smaller (20°) bearing angles. These positive results strengthen the evidence base for FPPs and establish the potential of MPPs as mobility devices for patients with hemianopia.

TRIAL REGISTRATION ClinicalTrials.gov NCT04827147, registered on 04/01/2021.