Retinal Prosthesis And Artificial Vision

E. Zrenner (1), F. Gekeler (1), K. Shinoda (1), K. Kohler (1), M, Völker (1), H. Gmeiner (1), A. Stett (2), W. Nisch, Hämmerle (2), K. Kobuch (3), H. Sachs (3), V.-P. Gabel (3), Z. Kisvarday (4), U. Eysel (4), M. Eger (5), M. Wilms (5), T. Schanze (5), R. Eckhorn (5)

(1) Univ.-Eye-Hospital, Tübingen; all Germany
(2) Nat. and Med. Science Inst, Reutlingen
(3) Univ.-Eye Hospital, Regensburg
(4) Dept. of Neurophysiology, Univ. of Bochum
(5) Dept. of Neurophysics, Univ. of Marburg

Aim
To develop a subretinal prosthesis to replace the function of lost photoreceptors in diseases like retinitis pigmentosa and age-related macular degeneration.
Methods and Results
Subretinal stimulation devices presented here consist of an array of microphotodiodes on a polyimide foil strip with electronic components to receive and store additional energy and control stimulation via TiN-electrodes. To control stimulus parameters also wire-bound devices with electrode arrays have been implanted via a novel ab-externo and an ab-interno access to the subretinal space (for a review see E. Zrenner et al., Vision Res. 39, 2555-2567 (1999); E. Zrenner, Science 295, 1022-1025 (2002)).
Multichannel recordings of electrically evoked cortical potentials show retinotopically correct cortical activation in pigs, rabbits and cats in acute and chronic trials with a possible spatial resolution of 1° of visual angle or better (R. Eckhorn et al., Ophthalmologe 98, 369-375 (2001); H. N. Schwahn et al., Graefes Arch.Clin.Exp.Ophthalmol. 239, 961-967 (2001)). Intrinsic signal optical imaging of the cat visual cortex has confirmed the function and achievable spatial resolution of the subretinal device (ARVO 2002, no. 2845). On the basis of in-vitro tests in healthy and degenerated retinae a resolution of 0.3° can be expected (A. Stett et al., Vision Res. 40, 1785-1795 (2000)).
Optical coherence tomography (OCT) showed that the retina was well attached after small initial edema and no further degeneration or damage could be observed (ARVO 2002, no. 4455). Histology has been performed in rabbits, pigs, and cats up to 29 months post-operatively. The retina tolerates the chip well, showing good embedment of the silicon device and preserved retinal architecture on top of the chip (K. Kohler et al., Ophthalmologe 98, 364-368 (2001)).
Conclusion
Several objective methods have proven that subretinal implants can activate the visual system in a spatially correct manner. The retina overlying the implant showed no signs of degeneration which would interfere with function. It therefore can be assumed that the concept of a subretinal visual prosthesis will be useful in helping patients who suffer from degenerative retinal disease.