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M. Pelizzone, A. Perez Fornos, K. Chanderli, A.B. Safran, P. Renaud, D. Bertrand, J. Salzmann, S. Picaud, J. Sommerhalder; Minimum Requirements for Useful Artificial Vision: Synthesis of Six Years of Research . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1539.
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© ARVO (1962-2015); The Authors (2016-present)
Within the framework of a large project aiming to develop a subretinal prosthesis, we assessed the minimum visual information needed to restore useful function to blind patients.
Visual perception with retinal prostheses will be severely limited. Devices will have a finite number of stimulation contacts that will fundamentally limit image resolution. Stimulation will be concentrated on a fixed, relatively small and probably eccentric retinal area. We studied the effects of these constraints using simulations of artificial vision on normal subjects. Performance on different every–day tasks such as full–page reading, visuo–motor coordination, and whole–body mobility in various environments was assessed, while systematically varying image resolution, image eccentricity, and the effective visual field (projected onto a 10°x7° retinal area).
For images projected onto the central visual field, results can be summarized as follows: (1) About 500 pixels are necessary for full–page reading. Strings of 4–6 characters and about two lines of text have to be visualized simultaneously for efficient reading, which corresponds to a (highly magnified) effective visual field of about 2°x1.4° for a typical newspaper. (2) About 400 pixels encoding an effective visual field of 16°x12° allow for efficient visuo–motor coordination. (3) As few as about 200 pixels encoding an effective visual field of 33°x23°allow for mobility in familiar environments. However, much higher image resolutions (>1000 pixels) were needed for subjects to feel safe in unpredictable environments including moving, eventually hazardous objects. In eccentric vision, initial performance was poor but all tasks could be performed after a period of systematic adaptation (30–70 training sessions at an eccentricity 15°).
About 500 phosphenes, retinotopically arranged over a 10°x7° retinal area, appear to be the minimum visual information required to restore useful function. Visual prostheses should aim to meet these criteria in order to provide efficient functional rehabilitation to blind patients. Our consortium is attempting to develop a retinal implant meeting these requirements.
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