Visual BOLD response in late-blind subjects with Argus II retinal prosthesis

Abstract

The recent advance in retinal prosthesis technologies generates hope for partially restoring vision to blind people with retinal pathologies. However, these strategies require the visual system downstream of the retinal circuitry to be capable of transmitting and elaborating visual signals. We studied plastic remodeling in late blind subjects implanted with Argus II Retinal Prosthesis. We assessed the visual function of a group of 7 blind patients before and after implantation. We measured motion direction discrimination, as well as detection of the same stimuli presented stationary to the operated and un-operated eyes in 2AFC design. We also recorded BOLD responses before and after the implant in four subjects in response to full-field flashing stimuli (1Hz) alternated with rest periods of dark. When the subjects used the prosthetic implant, detection discrimination improved over time, but not direction discrimination which remained at chance. No subject showed any improvement of vision in either eye when not aided by the Argus II. Before the implant the BOLD activity in the primary visual area and the putative LGN was very weak or absent, after surgery the response to visual inputs was enhanced. Interestingly this recovery was ipsilateral to the implant, implying that the neural changes are strictly correlated with the stimulation site. Given the evidence that the electrodes stimulate ganglion cells axons mainly from temporal hemiretina (Fine, Boynton Phil. Trans. R. Soc. B, 2015), our results suggest that local electrical stimulation may induce trophic factors and cause the enhancement in the activity of the LGN and V1 that receive afferents from temporal hemiretina. This is the first study tracking the neural changes of visual areas in patients after retinal implant and revealed a capability to respond to restored visual input even after years of deprivation. Meeting abstract presented at VSS 2016

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