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Takashi Fujikado, Kenta Hozumi, Takao Endo, Hiroyuki Kanda, Takeshi Morimoto, Motoki Ozawa, Kohji Nishida; Survey of candidates of STS retinal prosthesis in RP patients with hand-motion or less vision. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4555.
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In a pilot study of STS retinal prosthesis on patients with retinitis pigmentosa (RP) with hand-motion (HM) vision, results of light localization test (LLT) were not always better with devise on than off against a high contrast target (96%) but always better against a low-contrast (74%) target (Endo, Artificial Vision 2015). Before going to pivotal trial of STS retinal prosthesis using LLT as a primary outcome measure, we surveyed the proportion of RP patients with HM or less vision who cannot identify low contrast targets by residual vision but could identify by artificial vision. The ability to perceive phosphene by STS retinal prosthesis was predicted by trans-corneal electrical stimulation (TES) (Fujikado, IOVS 2016). A working hypotheses based on the pilot clinical trials are that patients can utilize phosphene by STS prosthesis effectively if threshold current by TES was less than 1.5mA and residual vision cannot identify a localized light (average deviation llarger than 400 pixels (16.7 degrees) in LLT).
Twenty eyes of 13 patients with RP with visual acuity equal or less than HM (OU) who visited Osaka University Hospital (age: 38-78) were examined. In TES examination, patients wore contact lens-type electrode and the threshold current of to elicit phosphene was examined. In LLT, a white square target (visual angle; 10 degrees) with high (96%) or low contrast (51%) was displayed on a PC monitor at a random position and patients were instructed to touch the center of a target (20 trials). We measured the distance between the touched point and the center of a target and averaged (absolute deviation (AD)).
Fifteen eyes (75%) of 10 patients perceived phosphene by TES with threshold current equal or less than 1.5mA. Among these, the number of eyes in which AD larger than 400 pixels was 10 (66%) against high- and 13 (87%) against low-contrast target. The number of patients who could be candidates of STS prosthesis was 5/13 (38%) by high-contrast target and 7/13 (54%) by low-contrast target.
Considerable proportion of RP patients with HM or less vision can be included in STS prosthesis trials if the outcome measure includes the accuracy of reaching against a low-contrast target.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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