Severe peripheral field loss (PFL) sometimes called tunnel vision is a result of retinitis pigmentosa and related diseases as well as glaucoma. Currently there are no effective visual aids for these patients whose mobility is seriously affected by this impairment. The novel concept of vision multiplexing as a design principle for low vision devices has provided guidance for the development of numerous devices for visual field losses. Spatial multiplexing by shifting, combined with biocular multiplexing, has been a proven effective aid for homonymous hemianopia. This approach, known as EP Prisms, uses unilateral prisms, and is applied to the peripheral field where double vision is well tolerated, and has evolved into a successful optical treatment. In numerous studies half or more of patients fitted with the EP prisms continue to wear and use the device over a long term and reported improved mobility. For PFL, Trifield prism spectacles, a biocular multiplexing device that applied central visual confusion to patients with tunnel vision (e. g., due to RP) has proven much more difficult. Despite there being no alternative aids available, and despite it being effective for 25% of patients, it has not made inroads in the marketplace. It is very complicated to construct and most patient find the central double vision it imposes disturbing. In considering the successful and limiting aspects of both approaches, the main requirements of patients with severe PFL, and the dynamic of a walking situation, we have designed a new visual aid, Quadrafield lens (creating artificial peripheral visual islands). This is achieved by applying near peripheral field expansion while avoiding the central confusion and fields tradeoffs of prior designs. We also invented a new optical element, a """"""""multiplexing prism"""""""" that can be applied to this and other devices. Multiplexing prisms provide simultaneous (monocularly) superimposed views of the shifted and direct see-through fields of view. The maintenance of the see through view permits treatment of monocular patients. It also permits fitting the prisms closer to the central field, as even with occasional encroachment, due to head movements, foveal vision is not completely blocked. In addition we have found a way to convert the regular vertical head bobbing motion into a lateral scanning through the prisms, implementing temporal multiplexing. Here we propose to implement, tune, and test the effectiveness of the multiplexing prisms as an aid for PFL, when used in the Quadrafield lens in laboratory studies and culminating in a multicenter randomized control clinical trial.
There is no acceptable visual aid for patients with severe peripheral field loss due to RP and glaucoma. We propose the development and testing of a new visual aid using a novel optical element and new design concepts. Following the proposed randomized-controlled multi center clinical trial to establish the effectiveness of the device, we will be able to bring an inexpensive and effective aid to the market which will lead to greater independence and improved quality of life of these patients.
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|Peli, Eli; Satgunam, PremNandhini (2014) Bitemporal hemianopia; its unique binocular complexities and a novel remedy. Ophthalmic Physiol Opt 34:233-42|