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C.G. Veraart, I. Obeid, M.E. Brelèn, J. Delbeke; Prospective on the Optic Nerve Visual Prosthesis . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1536.
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© ARVO (1962-2015); The Authors (2016-present)
To summarize the conclusions of the optic nerve visual prosthesis project thus far and to evaluate the potential for rehabilitating vision in retinopathy patients by electrically stimulating the optic nerve.
Two patients with retinitis pigmentosa (RP) have been implanted with the optic nerve visual prosthesis. The first patient received an intracranially (IC) implanted self–sizing spiral cuff electrode (four contacts) around her right optic nerve in 1998 at age 59. The second patient received an intraorbitally (IO) implanted spiral electrode (eight contacts) around his right optic nerve in 2004 at age 68. Optic nerve stimulations were controlled (via a telemetric link) by external equipment that included a head–worn video–camera and real–time image processing hardware. Phosphenes were first elicited under open–loop conditions, followed by psychophysical assessments conducted under closed–loop conditions. These included pattern recognition and an object localization, discrimination and grasping task. A mobility task that used a laser–based depth evaluation technique was also performed.
Both patients experienced phosphenes; although those of the IO patient were large and diffuse and thus unsuitable for closed–loop stimulations, those of the IC patient were small, well localized, and reproducible. Perception thresholds obtained with the IC patient were substantially lower than those measured in the IO patient; this was explained by the interposition of the dura mater between the electrode and the optic nerve in the IO patient. Psychophysical assessments conducted under closed–loop conditions with the IC patient demonstrated that, after training, she was able to recognize patterns from within a set of 45 with a success rate of above 85 % with an average recognition delay of 53 s. Object localization, discrimination and grasping tasks in the same patient were successfully completed in about 1 min. Performance in mobility tasks demonstrated the patient's ability to locate windows and doors along a corridor.
The results obtained thus far from the IC subject demonstrate the potential of the optic nerve visual prosthesis for restoring useful visual sensations to RP patients. Although closed–loop stimulations were not achieved with the IO subject, the dramatically less invasive nature of the IO implantation procedure remains attractive. Future designs could follow an IO based approach by using a new nerve electrode that would include stimulation spikes that would pierce the dura mater and thus place the contacts in closer proximity to the neural fibers.
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