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Delivery of Information and Power to the Implant, Integration of the Electrode Array with the Retina, and Safety of Chronic Stimulation

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Book cover Visual Prosthetics

Abstract

The fundamental function of a visual prosthesis is to deliver information about a patient’s surroundings to his/her neurons, usually via patterned electronic stimulation. In addition to transmitting visual information from the outside world to the implanted stimulating array, visual prostheses must also pass the electrical power necessary for such stimulation from the external world to the intraocular electrode array. The first section of this chapter reviews three common methods for achieving this data and power transfer: direct wireline connections (suitable for research studies), inductively coupled coils, and photodiode-based optical systems which utilize the natural optics of the eye.

Once the data and power has been received, retinal prostheses must effectively deliver stimulation currents to surviving retinal neurons. This necessitates an understanding of the electrode/retina interface. The second section of this chapter is a histological description of this interface for the case of subretinal implants, investigating the tissue response to flat implants coated with different materials. Several three-dimensional geometries are also described and evaluated to decrease the implant–neuron distance.

Finally, stimulation currents must not damage the stimulated neurons. The third section of this chapter describes measurements and scaling laws associated with tissue damage from electric currents. Damage thresholds are found to be approximately 50–100 times stimulation thresholds.

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Notes

  1. 1.

    The ED50 level for producing a minimally-visible lesion with near-IR light (λ  =  810–950 nm) for spot sizes larger than 1.7  mm on the retina and exposure times exceeding 1000s is 56  mW/mm2 [42, 43]. With a safety factor of 20, the maximum permissible exposure is then 2.8  mW/mm2.

Abbreviations

AC:

Alternating current

ASR:

Artificial silicon retina, a retinal prosthesis fabricated by Optobionics

CMOS:

Combined metal on silicon

CMP:

Computational molecular phenotyping

DC:

Direct current

EU:

European Union

IMI:

Intelligent medical implants, a company fabricating a retinal prosthesis

INL:

Inner nuclear layer

IR:

Infrared

LCD:

Liquid crystal display

MPDA:

Microphotodiode array, retinal prosthesis fabricated by retina implant AG

ONL:

Outer nuclear layer

P45:

45 days after birth

PI:

Propidium iodide

RCS rat:

Royal College of Surgeons rat, a common animal model of retinal degeneration

RF:

Radio frequency

RPE:

Retinal pigmented epithelium

SIROF:

Sputtered iridium oxide film

SU-8:

A photo-curable epoxy

USC:

University of Southern California

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  1. Department of Applied Physics, Stanford University, 450 Serra Mall, Stanford, CA, 94305, USA

    James Loudin

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  1. James Loudin
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  2. Alexander Butterwick
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  4. Daniel Palanker
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Correspondence to James Loudin .

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  1. , Lions Vision Research & Rehabilitation C, Johns Hopkins University School of Medic, 550 N. Broadway, Baltimore, 21205-2020, Maryland, USA

    Gislin Dagnelie

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Loudin, J., Butterwick, A., Huie, P., Palanker, D. (2011). Delivery of Information and Power to the Implant, Integration of the Electrode Array with the Retina, and Safety of Chronic Stimulation. In: Dagnelie, G. (eds) Visual Prosthetics. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-0754-7_7

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