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JJ Delbeke, M Oozeer, B Gérard, C Veraart; Comparison Between Optic Nerve Activation and Related Phosphenes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2843.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:The MIVIP and OPTIVIP projects involve the development of a visual prosthesis based on electrical stimulation of the optic nerve through an implanted spiral cuff electrode. In order to improve the understanding of the phosphene generation, experimental data have been compared with the results of modeling studies. Methods:This project fully complies with the Declaration of Helsinki, and was approved by the Ethics Committee of the School of Medicine and University Hospital of the University of Louvain, Brussels. The only volunteer involved up to now describes phosphenes whose attributes (threshold, localization, luminosity and size) are modified by the stimulation parameters. The electrical field generated by the stimulation as estimated using the finite element method is fed into an optic nerve axon model (S Parrini et al. Med Biol Eng Comput 2000; 38(4):454-64). The resulting activation maps are then translated into visual field coordinates, taking into account the central magnification. These models also provide optic nerve fibers recruitment curves. Results:The relative difference between the actual stimulus current and the perception threshold appears to provide the most representative control parameter. The influence of the stimulation parameters on the phosphene attributes can be modeled on the basis of relatively simple relationships. Phosphene size and position are very different from what could have been expected on the basis of the the retinotopically activated axons in the optic nerve. Conclusion:Basic attributes of the phosphenes can be reasonably controlled by the stimulation but some physiological mechanisms linked to the encoding schemes of the optic nerve remain to be investigated.
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