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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.
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