Nanotechnology in the Eye: First Visual Experience with Active Subretinal Implants

• Published in: Tissue engineering Vol. 13; no. 4; p. 870
• Main Author: Wrobel, W-G
• Format: Journal Article
• Language: English
• Published: 01.04.2007
• ISSN: 1076-3279

Retinitis pigmentosa, an inheritable disease causing blindness, is characterized by the degeneration of photoreceptors in the retina. The retinal network, however, stays intact. By electrically exciting bipolar or ganglion cells in the retina, it is possible to restore some visual sensation. Ever since research in active subretinal implants started more than 10 years ago, many in vitro as well as in vivo studies have been performed to determine stimulation parameters and to prove that electrical impulses can activate the retinal neural network. However, published reports about clinical results are rare, especially about the subjective visual experiences of patients. During epiretinal excitation, patients reported light sensations (phosphenes) with very different shapes. The first clinical results of subretinal excitation were reported only very recently. Therefore, one of the most important questions in retina implant development has been open: will a pattern of electrical excitation be recognized as an 'image'? We report the preliminary results of a pilot study that started in April 2006, in which two blind patients received an active subretinal implant. Using an array of 4x4 electrodes controlled externally, we could show for the first time that subretinal excitation generates phosphenes. When stimulating several electrodes simultaneously, phosphenes of similar shape and form were detected. The direction of a row or column of stimulating electrodes is recognized correctly. If electrodes are triggered successively, the apparent direction is also correctly identified. By comparing patients' verbal descriptions with the electrode dimensions, we concluded that the 50x50 mu m super(2) square, flat electrodes stimulate phosphenes with a diameter of up to 200 mu m.