Photodiode circuits for retinal prostheses

James D. Loudin, Stuart F. Cogan, Keith Mathieson, Alexander Sher, Daniel V. Palanker

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Photodiode circuits show promise for the development of high-resolution retinal prostheses. While several of these systems have been constructed and some even implanted in humans, existing descriptions of the complex optoelectronic interaction between light, photodiode, and the electrode/electrolyte load are limited. This study examines this interaction in depth with theoretical calculations and experimental measurements. Actively biased photoconductive and passive photovoltaic circuits are investigated, with the photovoltaic circuits consisting of one or more diodes connected in series, and the photoconductive circuits consisting of a single diode in series with a pulsed bias voltage. Circuit behavior and charge injection levels were markedly different for platinum and sputtered iridium-oxide film (SIROF) electrodes. Photovoltaic circuits were able to deliver 0.038 mC/cm2 (0.75 nC/phase) per photodiode with 50- μm platinum electrodes, and 0.54-mC/cm2 (11 nC/phase) per photodiode with 50-μ m SIROF electrodes driven with 0.5-ms pulses of light at 25 Hz. The same pulses applied to photoconductive circuits with the same electrodes were able to deliver charge injections as high as 0.38 and 7.6 mC/cm2 (7.5 and 150 nC/phase), respectively. We demonstrate photovoltaic stimulation of rabbit retina in-vitro, with 0.5-ms pulses of 905-nm light using peak irradiance of 1 mW/mm2. Based on the experimental data, we derive electrochemical and optical safety limits for pixel density and charge injection in various circuits. While photoconductive circuits offer smaller pixels, photovoltaic systems do not require an external bias voltage. Both classes of circuits show promise for the development of high-resolution optoelectronic retinal prostheses.
Original languageEnglish
Pages (from-to)468-480
Number of pages13
JournalIEEE Transactions on Biomedical Circuits and Systems
Volume5
Issue number5
DOIs
Publication statusPublished - 1 Oct 2011

Keywords

  • retinal prostheses
  • photodiode circuits
  • photonics

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    • 1 Visiting an external academic institution

    University of Stanford

    Keith Mathieson (Visiting researcher)

    Sep 2009Sep 2011

    Activity: Visiting an external institution typesVisiting an external academic institution

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