title: Improving the spatial resolution of epiretinal implants by increasing stimulus pulse duration.
abstract: Retinal prosthetic implants are the only approved treatment for retinitis pigmentosa, a disease of the eye that causes blindness through gradual degeneration of photoreceptors. An array of microelectrodes triggered by input from a camera stimulates surviving retinal neurons, with each electrode acting as a pixel. Unintended stimulation of retinal ganglion cell axons causes patients to see large oblong shapes of light, rather than focal spots, making it difficult to perceive forms. To address this problem, we performed calcium imaging in isolated retinas and mapped the patterns of cells activated by different electrical stimulation protocols. We found that pulse durations two orders of magnitude longer than those typically used in existing implants stimulated inner retinal neurons while avoiding activation of ganglion cell axons, thus confining retinal responses to the site of the electrode. Multielectrode stimulation with 25-ms pulses can pattern letters on the retina corresponding to a Snellen acuity of 20/312. We validated our findings in a patient with an implanted epiretinal prosthesis by demonstrating that 25-ms pulses evoke focal spots of light.
authors.affiliation: Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA. Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Weitz
authors.affiliation: Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Devyani
authors.initials: D
authors.lastname: Nanduri
authors.affiliation: Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Behrend
authors.affiliation: Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Gonzalez-Calle
authors.affiliation: Second Sight Medical Products Inc., Sylmar, CA 91342, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Greenberg
authors.affiliation: Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA. Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Humayun
authors.affiliation: Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA. Department of Physiology and Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA. jweiland@med.usc.edu rchow@med.usc.edu.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Chow
authors.affiliation: Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA. Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA. jweiland@med.usc.edu rchow@med.usc.edu.
authors.forename: James D
authors.initials: JD
authors.lastname: Weiland
mesh_terms: D000818:Animals; D015374:Biosensing Techniques; D004195:Disease Models, Animal; D004558:Electric Stimulation; D005074:Evoked Potentials, Visual; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D066298:In Vitro Techniques; D008839:Microelectrodes; D008904:Miniaturization; D009154:Mutation; D010641:Phenotype; D010719:Phosphenes; D011474:Prosthesis Design; D020318:Rats, Long-Evans; D012160:Retina / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000473:pathology; D012174:Retinitis Pigmentosa / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D012243:Rhodopsin / Q000235:genetics; D055366:Synaptic Potentials; D009435:Synaptic Transmission; D013997:Time Factors; D014162:Transfection; D014795:Visual Pathways / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D014796:Visual Perception; D057488:Visual Prosthesis
chemical_list: D012243:Rhodopsin