gms | German Medical Science

Artificial Vision — The 2nd Bonn Dialogue. The International Symposium on Visual Prosthesis

Retina Implant Foundation

19.09.2009, Bonn

Active subretinal implants: Design, functionality, and operational experience

Meeting Abstract

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Artificial Vision – The 2nd Bonn Dialogue. The International Symposium on Visual Prosthesis. Bonn, 19.-19.09.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ri25

DOI: 10.3205/09ri25, URN: urn:nbn:de:0183-09ri251

Veröffentlicht: 30. November 2009

© 2009 Wrobel.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

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The active subretinal implant has been designed based on MEA measurements with chicken retina samples. Threshold for excitation was determined to be 0.5 to 1 nC, with a dynamic range up to 10 nC/electrode. Achievable spatial resolution was estimated at 0.5°. In-vivo animal experiments in cats demonstrated cortical excitation with a resolution of approx. 1°.

The subretinal chip, designed and manufactured by IMS Stuttgart, is based on a CMOS camera technology, with 1500 Pixels on 3 x 3 mm², with a pixel size of 70 x 70 µm². Simulations of technically achievable visual results show a visual acuity of up to 0.1.

For initial testing purposes in a pilot study, the implant system also features an array of 4 x 4 electrodes, which are powered and controlled externally, allowing the exact determination of thresholds for visual sensations and electrode impedances.

The chip has a dynamic sensitivity range which allows to process 2–3 decades of brightness. This characteristic can be shifted by an external control voltage between 0.001 lx und 100 klx, allowing an adaptation to different lighting conditions. The chip is also sensitive in the Near-IR, giving the patient some night-vision capabilities.

Electrodes are made from fractal TiN. External power from a battery power supply behind the patient’s ear is transferred via silicone/gold cables and polyimide foils through the orbital cavity and the sclera to the subretinal chip. This external wiring did not limit the patients’ operative eye motility.

Electric field simulations show that within large, homogeneously stimulated areas the electric field in the center is less compared to the boundaries, leading to the clinical observation of bright “picture frames”.

Slight movements of the chip of typically <100 µm within the subretinal space were observed post-op, without any detrimental effect on the retina.

Patients perceived brightness and observed thresholds were in good agreement with laboratory measurements of the chip’s sensitivity characteristic. Most clinical testing was done at moderate light levels (10–1000 lx).

Patients were able to correctly discriminate grey levels, in accordance with chip characteristic. Landolt-C-testing was possible, with the smallest perceived structural details corresponding to a distance of 2–3 pixels only.

Correct functionality of the implant system can be checked by measuring the power consumption and the impedances at different chip connectors.

Chip function itself can be monitored by measuring ERG “artefacts”, with artefact amplitude correlated to chip illumination level.

This implant has been clinically tested in 11 blind patients with promising results (see presentation of E. Zrenner et al.).