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Eli Peli, Jae-Hyun Jung, Nish Mohith Kurukuti, Fernando Vargas Martin; High power multi-periscopic device for field expansion. Invest. Ophthalmol. Vis. Sci. 2018;59(9):638. doi: https://doi.org/.
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We have developed and evaluated a series of field expansion devices for visual field loss patients such as peripheral field loss (PFL) and homonymous hemianopia (HH), mostly based on prisms, and increased our understanding of the conditions, requirements and the impact of high power prisms in such applications. We recently found that the risk of a collision with other pedestrians (a common complaint) peaks when the other pedestrian is at 45° eccentricity (Peli, JoV 2016). However, the field expansion with current peripheral Fresnel prism glasses is limited to about 30° (57Δ). The shifted view with these high power prisms is distorted (minified), of low contrast, and dim. Due to total internal reflection, current prisms limit the effective range of eye scanning to only 5° into the blind field. To overcome these limitations, we invented a novel field expansion device, multi-periscopic prism (MPP).
With a cascade of half-penta prisms (commonly used in binoculars) we use double reflection rather than refraction to shift the scene with minimal loss of image quality. We developed MPP fitting configurations for HH and PFL for detection of lateral collision hazards and a new lateral MPP configuration for PFL. The latter is fitted to each carrier lens temporal to the optical center in base-out configuration elongated vertically allowing downward eye scanning to detect floor-level tripping hazards while maintaining lateral field expansion. We constructed the MPP prototypes using 3D-printed holders to cascade half-penta prisms and mount onto spectacle lenses.
The MPP prototypes demonstrate a 45° shift (100Δ, 50% over prisms) and permit up to 15° effective eye scanning range into the blind field (3 times wider than with Fresnel prisms), enlarging the coverage of collision detection particularly for PFL. The large angle shift was demonstrated in perimetry and the dramatically improved image quality (high contrast, lack of distortion and color dispersion) is illustrated using a special camera with accurate field presentation.
With the MPP, patients may be able to detect other pedestrians at eccentricities corresponding to the peak of the collision risk, while drivers with HH may be able to detect hazards at intersections where wider field and larger eye scanning range are required. The provision of the carrier optical correction further improved image quality.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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