The Amorphic Fresnel Prism Trioptical System
Severe visual field constriction, characteristic of conditions such as retinitis pigmentosa and end stage glaucoma creates significant limitations on an individual’s mobility and activities of daily living. In such cases, reverse telescopic systems have been utilized in an attempt to expand the visual field [1,2]. These image minification systems focus a larger field area on the remaining viable retinal tissue. The practicality of such systems is limited, however by the significant reduction in visual acuity resulting from the 360 degree minification. A -2.OX magnification system, for example, providing 2X expansion in field will reduce visual acuity by a factor of 0.5X. Also problematic are perceptual difficulties arising from vertical and horizontal displacement of the visual environment. Depth perception, so critical during mobility tasks, is greatly impaired by minification of the vertical meridian. Problems in correctly judging the position of stairs, curbs and irregularities on the road surface render the system impractical for continuous viewing while in motion.
KeywordsRetinitis Pigmentosa Full Field Horizontal Meridian Vertical Meridian Usher Syndrome
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