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GJ Suaning, YA Kerdraon, NH Lovell; Evoked Cortical Potentials From a CMOS Neurostimulation Circuit in Retinal Stimulation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4462.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Electrical stimulation of the retina may provide a means of eliciting controllable visual perception in humans affected by retinitis pigmentosa and other degenerative disorders. We have developed a complimentary metal oxide semiconductor (CMOS) stimulator capable of interfacing with 100 unique stimulation sites and tested various intra- and peri-ocular stimulating electrodes in their efficacy to produce a cortical response under conditions similar to those anticipated in chronic implantation. Methods: Surgery was performed on sheep under general anesthesia. Retinal stimulation was delivered both photically and electrically using various combinations of platinum electrodes inserted in the inferior conjunctival fornix, the central and epi-retinal vitreous, and the retrobulbar space. Recording electrodes were placed subdurally in the region of the visual cortex, and visual and electrical evoked potentials (VEP and EEP respectively) recorded. 30 mg/kg IV sodium iodate was used to alter the behavior of the retina such that the effects of degenerative disorders could be approximated. Results: Electrically evoked potentials were obtainable with all combinations of stimulating electrodes. Increasing stimulus charge injection resulted in an approximately linear increase in response amplitude for retrobulbar electrodes. Light adaptation was found to further increase this response. Sodium iodate administration eventually diminished both the VEP and EEP. From most to least effective electrode combinations using similar electrical stimulation parameters, electrode pairs tested were as follows: 1. Retrobulbar plate relative to intravitreal sphere; 2. Retrobulbar sphere relative to intravitreal sphere; 3. Intravitreal coaxial electrode. Discussion: Intravitreal coaxial electrodes required intimate contact with the epi-retinal surface before any evoked potential could be discerned. Retrobulbar electrodes (plate and sphere) when stimulated relative to intravitreal electrodes produced repeatable and significant responses indicative of stimulation of relatively large retinal surface area. Acute injection of sodium iodate had a profound influence on the retrobulbar stimulation which may be consistent with alteration of the passive trans-retinal electrical properties. Conclusion: Trans-retinal stimulation with this circuit may be a feasible approach for delivering mapped phosphenes without the need for intimate contact with the epi-retinal surface.
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