Document Detail

Frequency and amplitude modulation have different effects on the percepts elicited by retinal stimulation.
MedLine Citation:
PMID:  22110084     Owner:  NLM     Status:  MEDLINE    
PURPOSE: In an effort to restore functional form vision, epiretinal prostheses that elicit percepts by directly stimulating remaining retinal circuitry were implanted in human subjects with advanced retinitis pigmentosa RP). In this study, manipulating pulse train frequency and amplitude had different effects on the size and brightness of phosphene appearance.
METHODS: Experiments were performed on a single subject with severe RP (implanted with a 16-channel epiretinal prosthesis in 2004) on nine individual electrodes. Psychophysical techniques were used to measure both the brightness and size of phosphenes when the biphasic pulse train was varied by either modulating the current amplitude (with constant frequency) or the stimulating frequency (with constant current amplitude).
RESULTS: Increasing stimulation frequency always increased brightness, while having a smaller effect on the size of elicited phosphenes. In contrast, increasing stimulation amplitude generally increased both the size and brightness of phosphenes. These experimental findings can be explained by using a simple computational model based on previous psychophysical work and the expected spatial spread of current from a disc electrode.
CONCLUSIONS: Given that amplitude and frequency have separable effects on percept size, these findings suggest that frequency modulation improves the encoding of a wide range of brightness levels without a loss of spatial resolution. Future retinal prosthesis designs could benefit from having the flexibility to manipulate pulse train amplitude and frequency independently ( number, NCT00279500).
Devyani Nanduri; Ione Fine; Alan Horsager; Geoffrey M Boynton; Mark S Humayun; Robert J Greenberg; James D Weiland
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Publication Detail:
Type:  Comparative Study; Journal Article; Randomized Controlled Trial; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2012-01-20
Journal Detail:
Title:  Investigative ophthalmology & visual science     Volume:  53     ISSN:  1552-5783     ISO Abbreviation:  Invest. Ophthalmol. Vis. Sci.     Publication Date:  2012 Jan 
Date Detail:
Created Date:  2012-01-23     Completed Date:  2012-03-06     Revised Date:  2013-07-10    
Medline Journal Info:
Nlm Unique ID:  7703701     Medline TA:  Invest Ophthalmol Vis Sci     Country:  United States    
Other Details:
Languages:  eng     Pagination:  205-14     Citation Subset:  IM    
Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA.
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MeSH Terms
Blindness / etiology,  physiopathology,  rehabilitation*
Electric Stimulation Therapy / instrumentation*
Electrodes, Implanted*
Follow-Up Studies
Middle Aged
Retina / physiopathology*
Retinitis Pigmentosa / complications,  physiopathology,  rehabilitation*
Sensory Thresholds / physiology
Treatment Outcome
Visual Perception / physiology*
Grant Support
5R01EY012893-10/EY/NEI NIH HHS; P30 EY001730/EY/NEI NIH HHS; R01 EY014645/EY/NEI NIH HHS

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