Randomized crossover clinical trial of real and sham peripheral prism glasses for hemianopia

Abstract

Importance: There is a major lack of randomized controlled clinical trials evaluating the efficacy of prismatic treatments for hemianopia. Evidence for their effectiveness is mostly based on anecdotal case reports and open-label evaluations without a control condition.

Objective: To evaluate the efficacy of real relative to sham peripheral prism glasses for patients with complete homonymous hemianopia.

Design, setting, and participants: Double-masked, randomized crossover trial at 13 study sites, including the Peli laboratory at Schepens Eye Research Institute, 11 vision rehabilitation clinics in the United States, and 1 in the United Kingdom. Patients were 18 years or older with complete homonymous hemianopia for at least 3 months and without visual neglect or significant cognitive decline.

Intervention: Patients were allocated by minimization into 2 groups. One group received real (57-prism diopter) oblique and sham (<5-prism diopter) horizontal prisms; the other received real horizontal and sham oblique, in counterbalanced order. Each crossover period was 4 weeks.

Main outcomes and measures: The primary outcome was the overall difference, across the 2 periods of the crossover, between the proportion of participants who wanted to continue with (said yes to) real prisms and the proportion who said yes to sham prisms. The secondary outcome was the difference in perceived mobility improvement between real and sham prisms.

Results: Of 73 patients randomized, 61 completed the crossover. A significantly higher proportion said yes to real than sham prisms (64% vs 36%; odds ratio, 5.3; 95% CI, 1.8-21.0). Participants who continued wear after 6 months reported greater improvement in mobility with real than sham prisms at crossover end (P = .002); participants who discontinued wear reported no difference.

Conclusions and relevance: Real peripheral prism glasses were more helpful for obstacle avoidance when walking than sham glasses, with no differences between the horizontal and oblique designs. Peripheral prism glasses provide a simple and inexpensive mobility rehabilitation intervention for hemianopia.

Trial registration: clinicaltrials.gov Identifier: NCT00494676.

Figure 1. Permanent peripheral prism glasses as fitted for the study

Shown here with prisms on the left spectacle lens for a patient with left hemianiopia, with 12mm inter-prism separation: (a) Horizontal design, 57Δ (base-apex axis horizontal); (b) Oblique design, 57Δ (base-apex axis at 25°); and (c) Sham horizontal, 5Δ. The oblique design provided visual field expansion in more central areas of the visual field than the horizontal design (Figure 2). Each patient wore real (57Δ) prisms of one design and sham (5Δ) prisms of the other design (e.g., real oblique (b) and sham horizontal (c))

Figure 2. Binocular visual field (Goldmann V4e) of a patient with left HH

(a) Without peripheral prisms; (b) with 57Δ horizontal peripheral prisms; and (c) with 57Δ oblique peripheral prisms, as fitted for the study with a 12mm inter-prism separation. Both designs provide close to 30° of lateral expansion into the blind hemifield (slightly more for the horizontal than the oblique design). The expansion is in more central areas of the field with the oblique design. Small black squares are the individual points mapped during the perimetry.

Figure 3. Participant flow through the study

Minimization was used to allocate participants to treatment group and sequence: real oblique AB/BA and real horizontal AB/BA (AB = Real first; BA = Sham first).

Figure 4. Mean mobility improvement scores for real and sham prism glasses

Participants who continued prism wear reported significantly more improvement with real than sham glasses. Mobility scores are in logit units: more positive values represent greater improvement. For real and sham prisms, error bars are 95% confidence intervals of the mean scores. For the difference between real and sham, errors bars are 95% confidence intervals of the mean paired differences.

Figure 5. Median relative ratings of real and sham prism glasses from the comparison questionnaire

(a) Ratings for obstacle avoidance and (b) ratings for vision comfort, grouped by whether participants selected real prism glasses (n = 37), sham prism glasses (n = 16) or neither pair of prism glasses (n = 8). Responses of participants who selected real prism glasses were significantly different from those who selected sham or neither. Participants who selected real prism glasses rated them as much better than the sham; whereas, those who selected sham glasses rated them as only slightly better than the real glasses. (Participants, still masked when this questionnaire was administered, gave rankings in terms of first pair or second pair, which were subsequently converted to real or sham. Scale: −2 = Sham much better; −1 = Sham slightly better; 0 = No difference; 1 = Real slightly better; 2 = Real much better). Thick vertical line within each box is the median; box length is the interquartile range (IQR); whiskers represent the range of the data within 1.5x IQR; open circle: outlier within 1.5x – 3x IQR; open triangle: far outlier beyond 3x IQR.