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Michael P Barry, Gislin Dagnelie; Stability and Adaptation of Light Localization in Retinal Prosthesis Users with External Cameras. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1817.
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© ARVO (1962-2015); The Authors (2016-present)
Demonstrate stability of light localization abilities in subjects with retinal prostheses that use external cameras, and characterize adaptation of such localization when camera and implant representations are intentionally misaligned.
Three end-stage RP patients implanted with the Argus® II epiretinal prosthesis participated in this study. Participants touched a white square on a black background on a touchscreen monitor. Subjects were given auditory feedback including whether they were correct, and if not, the location of the target relative to the location touched. The distribution of errors was used to determine the accuracy and precision of light localization. Typical targets had sides spanning 5° of visual field. To demonstrate localization stability, captured images were digitally centered on the direction subjects associated with the stimulated area of the retina (aligned condition), and these settings were maintained for two months. Captured images were subsequently misaligned by 10-30°, and held at this setting for periods of 9-10 months to monitor adaptation. Statistical tests were based on bootstrap resampling of data.
All subjects demonstrated accurate and stable target localization for over 1 month. Two subjects demonstrated stable localization for the entire 2 month period. Over periods of 7-8 months, with corrective auditory feedback, two subjects became more accurate at localization at rates of 0.03°-0.06°/day (p < 0.005), while one subject’s inaccurate localization remained unchanged. The rates of adaptation observed here are 8000 times slower than that seen in sighted subjects with prism glasses. When auditory feedback was removed, one subject who had demonstrated adaptation unlearned all corrections, while the other retained some adaptation without feedback.
These results demonstrate that the localization abilities of patients that use retinal prostheses with external cameras can remain stable over an extended period of time, although regular evaluation may be necessary to maintain accuracy. If a patient has a misaligned camera setting, accuracy can be improved with feedback; however, recalibration of the external camera may be necessary to provide persistent corrections to errors. Further experiments will be performed without auditory feedback to more thoroughly assess localization stability with both aligned and misaligned camera settings.
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