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

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.

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.

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.

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.

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