An Optoelectronic Pulse Frequency Modulation Circuit for Retinal Prosthesis

A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the circuit is described and analyzed. The circuit is realized in 0.6μm CMOS process,and the simulation results testify to the possibility of sub-retinal implantation.

A cascade model of information processing and encoding for retinal prosthesis

Retinal prosthesis offers a potential treatment for individuals suffering from photoreceptor degeneration diseases.Establishing biological retinal models and simulating how the biological retina convert incoming light signal into spike trains that can be properly decoded by the brain is a key issue.Some retinal models have been presented,ranking from structural models inspired by the layered architecture to functional models originated from a set of specific physiological phenomena.However,Most of these focus on stimulus image compression,edge detection and reconstruction,but do not generate spike trains corresponding to visual image.In this study,based on stateof-the-art retinal physiological mechanism,including effective visual information extraction,static nonlinear rectification of biological systems and neurons Poisson coding,a cascade model of the retina including the out plexiform layer for information processing and the inner plexiform layer for information encoding was brought forward,which integrates both anatomic connections and functional computations of retina.Using MATLAB software,spike trains corresponding to stimulus image were numerically computed by four steps：linear spatiotemporal filtering,static nonlinear rectification,radial sampling and then Poisson spike generation.The simulated results suggested that such a cascade model could recreate visual information processing and encoding functionalities of the retina,which is helpful in developing artificial retina for the retinally blind.

Electrical stimulation scheme optimization for retinal prosthesis:considerations from biological perspective

Effective and safe electrical stimulation of the retinal ganglion cells is at the heart of retinal prosthesis design.However,the effectiveness and safety demand of the electrical stimulation is often at odds against each other.Besides,the nerve fiber layer above retinal ganglion cells limits the spatial resolution of stimulation.Also,current retinal prosthesis still cannot selectively activate the ON or OFF visual pathways,thus cannot relay the correct luminance information to the brain.With decades of development,the stimulation protocol for retinal implants began to tackle these problems.We believe that a novel design of electrical stimulation scheme,combined with gene therapy technique,can improve the selectivity and spatial resolution of retinal implants and further lower the damage caused by electric stimulation.

AB032. Exploring the effects of a retinal prosthesis on visual hallucinations related to Charles Bonnet syndrome

Background:A first occurrence in the province of Quebec(Canada)of the use of a retinal prosthesis system(RPS)by a patient with a Charles Bonnet syndrome(CBS)provides a rare opportunity to explore the effects of this system on visual hallucinations(VH)related to CBS.Considering that the RPS artificially induces a visual perception and that VH related to CBS occur in cases of significant vision loss,this study aimed to explore whether the recovery of a visual perception could affect the nature and frequency of VH related to CBS.Methods:This is a case study with time series and repeated experimentation:a pre-intervention measure to establish the baseline level,two implant activation periods(A1 and A2)and a post-intervention measure(3 for each activation).The study is based on a 65-year-old man with retinitis pigmentosa.He has been functionally blind for about ten years and was completely blind at the time of the study.He began to perceive VH corresponding to the CBS after a significant decrease of his visual fields.At the time of the study,these VH were frequent and often disturbing.After receiving the Argus II RPS,he participated,along with INLB staff,in an intensive rehabilitation program aiming at optimizing the use of the system.To explore the effects of the RPS,we collected visual,cognitive,and mood-related data and documented the VH using the Charles Bonnet Syndrome Screening Questionnaire(Cantin et al.,2018).Results:The visual acuity and visual field measurements show a significant improvement with the use of the RPS(visual acuity of 2.3 logMAR and visual fields of 12 degrees).Measurements of cognitive functions have shown high,stable,and close to the maximum performances.Mood data revealed low and relatively stable depression and anxiety scores over the course of the study.The documented VH showed the characteristic features of CBS.The nature and frequency of VH have varied widely over the study period.Conclusions:The RPS improved the visual perceptions of the study participant and VH that were observed correspond to the CBS definition.Despite the partial recovery of some form of visual perception induced by the RPS,the variations in the nature and frequency of the VH have occurred independently of the use of the system:therefore,they cannot be linked.While it is true that the Argus II RPS allows blind users to recover some form of visual perception,it remains very limited and the implanted subject remains functionally blind.It is then legitimate to assume that the visual perceptions generated by the implant may be insufficient to have an effect on VH related to CBS.Further studies are needed to support the conclusions of this innovative study.

Retinal Prosthesis:A Potential Benefit for the Blind

Retinal degenerative diseases may induce the degeneration of outer retina and in turn,blindness.Nevertheless,due to the maintenance of inner retina,the coding and processing of visual neurons responses are still able to be executed naturally.Therefore,an effective retinal prosthesis device may be developed by mimicking the function of outer retina:transferring the visual light into artificial stimulus and delivering the stimulus to the retina aiming to evoke the neural responses.As two main developing directions for current retinal prosthesis,epiretinal(ER)and subretinal(SR)prosthesis are both undergoing experimental stage and possessing advantages and limitations.Further investigations in power supply,biocompatibility,etc.are still required.Additionally,suprachoroidal transretinal stimulation(STS)and neurotransmitter-induced stimulation as some other alternatives in retinal prosthesis are also considered as promising research directions,although they are not mature enough to be applied commercially,either.

Safety,effectiveness,and cost-effectiveness of ArgusⅡin patients with retinitis pigmentosa:a systematic review

AIM:To assess the effectiveness,safety,and costeffectiveness of the Argus II in treatment of the retinitis pigmentosa(RP)patients.METHODS:The Pro Quest,Web of Science,EMBASE,MEDLINE(via Pub Med)were searched using combinations of the keywords of Argus,safety,effectiveness,bionic eye,retinal prosthesis,and RP through March 2018.The retrieved records were screened and then assessed for eligibility.RESULTS:Totally 926 records were retrieved from the searched databases and finally 12 studies included.The RP patients showed improvements in visual function after receiving the prosthesis,compared to the time before the prosthesis or the time it was off.This was measured by square localization,direction of motion,and grating visual acuity tests.No major adverse effect was reported for the Argus II prosthesis itself and/or the surgery to implement it,but the most frequently reported items were hypotony,and conjunctival dehiscence.The incremental cost-effectiveness ratio(ICER)was calculated to be€14603 per qualityadjusted life year(QALY)in UK and$207616 per QALY in Canada.CONCLUSION:The available evidence shows that the Argus II prosthesis in RP patients is effective in improvement of their visual function.Some minor adverse effects are reported for the prosthesis.The cost-effectiveness studies show that the technology is cost-effective only at high levels of willingness-to-pay.