Physiological response in Ovis aries resulting from electrical stimuli delivered by an implantable vision prosthesis

An implantable vision prosthesis has been developed to deliver externally controlled, charge balanced, constant current, biphasic electrical stimuli to the inner retina. The device is intended as a treatment to blindness. Specifically, degenerative disorders of the retina such as retinitis pigmentosa, macular degeneration, choroideremia, etc. would be treated with such a device. Many profoundly blind patients suffering from the aforementioned conditions are plagued with sleeping disorders associated with the loss of photic input. Restoration of light and dark perception may serve to restore circadian rhythm and thus this has been set as the initial goal for the device. In an effort to confirm the device´s ability to provide light and dark perception an implantable electrode with a 3.9 mm² contact area was inserted into the posterior eye chamber of the Ovis aries (common name: sheep). Using this electrode, stimuli from the implant were applied to the inner retina and an ensemble averaged evoked potential was successfully recorded from the visual cortex using sub-dural electrodes. This resulted in an electrically induced visual evoked potential with peak amplitude of 140 ± 20 μV (N = 3) that was qualitatively similar to a visual evoked potential evinced using stroboscopic light stimuli.