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Norman Sabbah, Colas N Authié, Nicolae Sanda, Saddek Mohand-Saïd, Jose Alain Sahel, Avinoam B Safran; Importance of eye position on spatial localization in blind subjects wearing a camera-connected retinal prosthesis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1816.
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© ARVO (1962-2015); The Authors (2016-present)
With a camera-connected type of retinal prosthesis (CC-P), exploration of the visual environment is achieved by head (i.e., camera) movements; recorded visual information is then processed to electrically stimulate speared cells in the retina. Considering that in normal individuals, spatial localization of viewed images is determined by eye position, and that in CC-P wearers head (i.e., camera) and eye directions can be dissociated, we investigated whether varying eye position while keeping the head still, affects perceived localization of CC-P generated images.
We studied 3 individuals blinded by retinitis pigmentosa, and wearing a CC-P (Argus® II, Second Sight Medical Products, Sylmar, California). Presented with a light spot on the center of a touch screen, they were requested to orient their gaze into 5 predetermined directions, and to finger-point on the screen corresponding perceived spot locations. 50 trials (10 at each tested location) were randomly performed. Coordinates of the pointed locations were grouped according to gaze directions, and processed to investigate for significance in differences (evaluated by Mann-Whitney test with Bonferroni correction). In addition, careful history was taken on subjects' every day behavior when performing visually directed grasping tasks.
Pointing coordinates could be collected in two subjects. The third individual failed to comply with test requests. Results showed that for both reliable subjects, median pointing directions were shifted towards the gaze direction (Mann-Whitney test, p<0.01), except for subject 2, in which the shift downward was not statistically significant. Moreover, it appeared that the subjects did not precisely perceive their eye position, and developed strategies for performing visually directed movements.
Eye position determines perceptual localization of Argus® II retinal prosthesis generated images, and consequently affects visuo-motor coordination. However, Argus® II wearers use adaptive strategies when performing visually guided movements. Our observations provide valuable indications for rehabilitation procedures and for the design of upcoming retinal prosthesis generations.
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