How to assess and compare visual function in blind patients with electronic neuroprostheses?

Abstract

Abstract: : Purpose: Electronic prostheses for restitution of visual function have been developed for subretinal and epiretinal coupling, as well as for the optic nerve and the visual cortex. There is a need for standardized procedures to assess the functional outcome gained by the image transfer properties of such devices. Methods: In order to define a minimum set of tests that assess the characteristics of neuroprostheses for visual functions, we propose laboratory tests based strictly on psychophysical threshold assessments additionally to descriptions of field experiments. Tests are presented on a high luminance display screen (max.700 cd/m2) subtending 25° by 15°. In an increasing series of visual processing demands, psychometric functions are determined by an automated test procedure, taking account of learning and variability. 1. Fixation: Presentation of a bright dot, so that the patient can localize the area where to expect a test target after a tone; measuring time until target is found. 2. Light perception: the patient is being presented 1 or 2 Ganzfeld flashes (with an interval t1) and indicates whether 1 or 2 flashes were seen. 3. Temporal resolution: the interval t1 is varied between the 2 flashes. 4. Location: In addition to a continuous fixation target, a circular stimulus appears at one of 8 different locations with a fixed eccentricity e1. 5. Motion: a random multi–hexagonal black and white pattern of high contrast with an individual hexagon subtending 1° of visual angle is moved in 8 different directions. Frequency–of–seeing characteristics are obtained for various speeds and contrasts. 6. Further test subunits include spatial resolution and contrast vision by varying size and luminance of targets, optokinetic nystagmus and pupillary light reflexes supplemented by assessing a standardized life quality assessment form. Conclusions:We recommend a battery of computerized, standardized tests for patients with visual prostheses to quantify the functional outcome. Common clinical tests insufficiently describe improvements gained by various chip–types, because these test settings are prone to a number of effects not necessarily related to chip–performance.

Keywords: retina • retinal degenerations: hereditary • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials