title: Retinal charge sensitivity and spatial discrimination obtainable by subretinal implants: key lessons learned from isolated chicken retina.
abstract: In order to obtain functional parameters relevant to the designing of a subretinal implant, we carried out electrical stimulation experiments with isolated chicken retina. The median threshold for network activation with planar disc electrodes (diameter 10 microm) was 0.5 nC (625 microC cm(-2)) for anodal voltage impulses and 1.6 nC (2 mC cm(-2)) for cathodal impulses. Above threshold, the number of spikes evoked by a single voltage impulse increased up to saturation within a range of injected charge from 0.1 nC to 1 nC for anodal impulses and from 1 nC to 10 nC for cathodal impulses. Using needle electrodes with a tip diameter of 1 microm, we determined the electrical point spread function (EPSF) for subretinal stimulation. It had a half width in the range of 100 microm, which corresponds to a visual angle of 21' and to a visual acuity of 20/417 in the human eye. It is reasonable to conclude that with subretinal implants the minimum separable will be of the same dimension.
authors.affiliation: Natural and Medical Sciences Institute at the University of Tuebingen, Markwiesenstr. 55, 72770 Reutlingen, Germany. stett@nmi.de
authors.forename: Alfred
authors.initials: A
authors.lastname: Stett
authors.forename: Andreas
authors.initials: A
authors.lastname: Mai
authors.forename: Thoralf
authors.initials: T
authors.lastname: Herrmann
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002645:Chickens; D004056:Differential Threshold; D004558:Electric Stimulation / Q000295:instrumentation* / Q000379:methods; D004567:Electrodes, Implanted; D019544:Equipment Failure Analysis; D005071:Evoked Potentials / Q000502:physiology; D009415:Nerve Net / Q000502:physiology*; D019736:Prostheses and Implants; D015203:Reproducibility of Results; D012160:Retina / Q000502:physiology*; D012680:Sensitivity and Specificity; D013028:Space Perception / Q000502:physiology*