Related Experiment Video
Updated: Mar 9, 2026
Virtual Prism Adaptation Therapy: Protocol for Validation in Healthy Adults
Published on: February 12, 2020
A pilot randomized controlled trial comparing effectiveness of prism glasses, visual search training and standard
F J Rowe1, E J Conroy2, E Bedson3
1Department of Health Services Research, University of Liverpool, Liverpool, UK.
Objective:
Pilot trial to compare prism therapy and visual search training, for homonymous hemianopia, to standard care (information only).
Methods:
Prospective, multicentre, parallel, single-blind, three-arm RCT across fifteen UK acute stroke units.
Participants:
Stroke survivors with homonymous hemianopia.
Interventions:
Arm a (Fresnel prisms) for minimum 2 hours, 5 days per week over 6 weeks. Arm b (visual search training) for minimum 30 minutes, 5 days per week over 6 weeks. Arm c (standard care-information only).
Inclusion Criteria:
Adult stroke survivors (>18 years), stable hemianopia, visual acuity better than 0.5 logMAR, refractive error within ±5 dioptres, ability to read/understand English and provide consent.
Outcomes:
Primary outcomes were change in visual field area from baseline to 26 weeks and calculation of sample size for a definitive trial. Secondary measures included Rivermead Mobility Index, Visual Function Questionnaire 25/10, Nottingham Extended Activities of Daily Living, Euro Qual, Short Form-12 questionnaires and Radner reading ability. Measures were post-randomization at baseline and 6, 12 and 26 weeks.
Randomization:
Randomization block lists stratified by site and partial/complete hemianopia.
Blinding:
Allocations disclosed to patients. Primary outcome assessor blind to treatment allocation.
Results:
Eighty-seven patients were recruited: 27-Fresnel prisms, 30-visual search training and 30-standard care; 69% male; mean age 69 years (SD 12). At 26 weeks, full results for 24, 24 and 22 patients, respectively, were compared to baseline. Sample size calculation for a definitive trial determined as 269 participants per arm for a 200 degree2 visual field area change at 90% power. Non-significant relative change in area of visual field was 5%, 8% and 3.5%, respectively, for the three groups. Visual Function Questionnaire responses improved significantly from baseline to 26 weeks with visual search training (60 [SD 19] to 68.4 [SD 20]) compared to Fresnel prisms (68.5 [SD 16.4] to 68.2 [18.4]: 7% difference) and standard care (63.7 [SD 19.4] to 59.8 [SD 22.7]: 10% difference), P=.05. Related adverse events were common with Fresnel prisms (69.2%; typically headaches).
Conclusions:
No significant change occurred for area of visual field area across arms over follow-up. Visual search training had significant improvement in vision-related quality of life. Prism therapy produced adverse events in 69%. Visual search training results warrant further investigation.
