Visual Field Expansion Through Innovative Multi-periscopic Prism Design

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Individuals with visual field loss report collisions with other pedestrians or objects, tripping over obstacles, and are commonly not permitted to drive. All of these factors severely restrict their independence and quality of life. Visual field loss is common following brain injuries such as stroke, trauma, or tumors (hemianopic field loss, HFL) or it may be due to retinal diseases such as retinitis pigmentosa, choroideremia, and advanced glaucoma (peripheral field loss, PFL). Most visual aids developed for field expansion have had limited success. Prisms designed to shift portions of a scene from the blind field to the residual seeing field are the simplest, lightest, and most cost-effective devices for visual field loss patients. These prism devices create artificial visual islands that can help PFL and HFL patients detect and avoid collision risks. A pedestrian on a collision course will stay at a fixed position in the visual field of the patient. Our recent analysis found that the risk of a collision with other pedestrians is highest when the oncoming pedestrian approaches from an angle of 45. Conventional prism devices can shift images up to 30° but do not reach this area of peak collision risk. Further, the shifted images are distorted spatially (minified) and in color and have low contrast. When patients scan (look) toward the blind side the effective expansion benefit is limited to only 5° by current prism designs. Thus, the actual field expansion benefit of current devices falls below the best possible theoretical expectation. To overcome these limitations, we invented a new optical device, the “multi-periscopic prism (MPP)”, which uses cascaded half-penta prisms (typically used in binoculars). Whereas conventional prisms use refraction, the MPP uses two reflections, resulting in a 45° image shift (improvement of 50% over current prisms) without the refraction effects of minification, color distortion, or contrast reduction. The MPP covers the peak collision risk eccentricity and permits 15° of effective eye scanning into the blind side (3 times wider than current prisms). We developed prototypes and preliminary configurations of this novel device to enable field expansion in HFL and PFL patients. This field expansion is intended to facilitate detection of pedestrian collisions when walking, or hazards at intersections when driving (HFL). We have proposed configurations of the device for PFL patients to allow for downward eye scanning and detection of tripping hazards. Here we propose to iteratively implement additional refinements, fine-tune, and test the effectiveness of the MPP as an aid for patients with HFL or PFL. This will begin with feasibility tests in the lab and culminate in a randomized controlled multicenter clinical trial. We will compare patients’ pedestrian collision detection performance with the novel MPP devices and current prism devices and evaluate their device preferences. In the multicenter clinical trial, we will use an innovative virtual reality pedestrian collision detection test system that can be easily implemented at clinics using standard computers and large screen TVs. We will also conduct a lab test during the multi-center clinical trial to further study the efficacy of the MPP in HFL driving.