gms | German Medical Science

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

Retina Implant Foundation

19.09.2009, Bonn

A visual prosthesis based on suprachoroidal-transretinal stimulation

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. Doc09ri15

DOI: 10.3205/09ri15, URN: urn:nbn:de:0183-09ri155

Veröffentlicht: 30. November 2009

© 2009 Terasawa.
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

Text

We have been developing a visual prosthesis based on suprachoroidal-transretinal stimulation (STS). In STS, electrical stimulation is achieved by applying a current pulse between a stimulation electrode array implanted in the sclera and a return electrode placed in the vitreous cavity. The prime advantage of STS is its low-invasiveness to the eye due to the placement of the stimulation electrode array outside the eyeball.

In our system, an electrical circuit contained in a hermetic package is placed under the skin behind the patient’s ear. Charge-balanced biphasic current pulses are sent from the circuit to the electrode array placed in suprachoroidal area via parylene-insulated, helically-wound cables. Each cable is directly welded to an electrode. The electrode array consists of bullet-shaped platinum electrodes and a substrate made from parylene to which the electrodes are fixed. The diameter and the height of each electrode are both 500 µm. The electrode array is curved to fit the eye. To check the long-term durability of the implant, a soak test in 37°C phosphate-buffered saline was conducted for 6 month and no device failure was observed. To examine the safety of electrical stimulation, testing of long-term stimulation of rabbits’ eyes has been conducted using the above-mentioned bullet-shaped electrodes. Although this trial is still underway, preliminary results suggest that a charge injection of up to 0.7uC/phase does not show a significant correlation with the occurrence of tissue damage. Additionally, from histology, it can be inferred that an appropriate thickness of the residual sclera between the electrode array and choroid is critical for preventing damage to the retina.

Currently we are preparing for clinical study of a wirelessly-powered and -controlled device implanted for one month. At the same time, we are developing a next-generation device that includes a hermetic package small enough to be placed onto the eyeball. In addition, we are trying to improve the charge delivery capacity of the bullet-shaped electrodes by roughening their surfaces with electrochemical etching.