Measurement of Evoked Potentials after Electrical Stimulation of the Human Optic Nerve

Purpose. To examine the visual evoked potentials (VEP) and electroretinograms (ERG) generated during electrical stimulation of the human optic nerve using the optic nerve visual prosthesis (ONVP). Methods. Two volunteers, both blind with no light perception from retinitis pigmentosa (RP), were chronically implanted with the optic nerve visual prosthesis. Cortical evoked potentials were recorded using 16 scalp electrodes and antidromic ERGs were obtained using DTL electrodes whilst electrically stimulating the optic nerve. The results were compared with flash and eye surface electrical stimulation results in normal sighted control subjects. Results. The VEPs obtained in our two implanted volunteers have a similar waveshape to those obtained in normal sighted volunteers during flash stimulation but latency is reduced by about 25 ms. The VEP recorded during surface eye stimulation are similar in both normal sighted and RP volunteers. The VEPs were compared at sub- and supra-threshold stimulation strength and with different electrode configurations. Finally, the antidromic ERG recordings obtained in our implanted volunteers show a unique inner retinal potential generated by retrograde stimulation of the eye from the optic nerve. Conclusion. Evoked potentials can be used to examine how a visual prosthesis generates visual sensations. This provides an objective means to investigate various aspects of the visual prostheses.