Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-04-23
2001-10-02
Manuel, George (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06298270
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of retina implants, in particular to epiretinal and subretinal implants having a substrate with a surface for applying the implant with that surface to the retina, and wherein the substrate comprises electrodes for stimulating cells within the retina. The electrodes are provided on the surface and are exposed to visible light entering into the eye and impinging on the retina such that stimuli are exerted on the cell by way of the electrodes.
BACKGROUND OF THE INVENTION
Retina implants of various kinds are well-known in the prior art. For example, European published patent application 0 460 320 discloses a subretinal implant to be implanted between lower layers of the retina. This prior art implant essentially consists of a silicon chip configured by a large number of densely packed microphotodiodes. The photoactive surface of the photodiodes is directed to the light impinging through the eyes on the retina. The photodiodes generate an amplitude modulated current stimulating the cellular layer of the retina lying on the implant surface. By using such implant it shall be possible to enable patients suffering from retinal degenerations to improve or even regain vision.
The prior art implant is configured such that the impinging ambient light shall be sufficient to generate the required stimuli for the retinal cells. Hence, an external energy supply is not provided.
In the scientific journal IEEE Spectrum of May 1996, pp. 47-53, still another retina implant is disclosed which, however, shall be used as an epiretinal implant. Consequently, this prior art implant has an electrode surface which is placed between the vitreous body of the eye and the retina surface for stimulating ganglion cells located just below the retina surface.
In contrast to the situation with subretinal implants, when epiretinal implants are used, it is necessary to encode the stimuli in order to compensate for the biological variations to which the biological signals are subjected on their way between the photoreceptors and the ganglion cells in the lower retinal layers. Epiretinal implants are, therefore, controlled externally, namely on the basis of an image which, for example, is generated by a video camera or the like which, in turn, may be configured as spectacles for a patient.
in view of these systematic distinctions between subretinal implants and epiretinal implants, the latter are larger in view of their specific design, are more complicated and have a higher energy consumption.
In the prior art epiretinal implant mentioned before, the image viewed by the patient is recorded by means of a CCD-camera which, together with a signal processing chip and a laser are provided in a spectacle-like device.
Within the implant itself the electrode array that is provided for stimulating the ganglions, is configured as a thin blade extending laterally from the implant as such. The blade is placed on the retina. The implant body as such is configured relatively bulky. Further to a stimulator chip it comprises a photodiode array being directed against the eye opening. The photodiode array receives a light signal from the laser being arranged in the spectacle-like device. The light signal is within the visible portion of the spectrum and contains the image signals on the one hand side and, further, light energy used for the implant energy supply.
It is, therefore, a disadvantage of this prior art epiretinal implant that a considerable portion of the surface in the area of the retina must be obscured by the photodiode array in order to ensure the necessary signal transmission and power supply. That portion of the retina which is obscured by the implant may, hence, not used for stimulation. Further, the amount of energy that may be transmitted into the eye is limited by the physiological threshold of the retina with respect to visible light.
In a subretinal implant of the kind mentioned at the outset, the problem is that ambient light may be insufficient to generate stimuli of sufficient amplitude being larger than the stimulus threshold of the retinal cells to be stimulated.
It is, therefore, an object underlying the invention to improve an implant of the kind mentioned at the outset such that even under poor ambient light conditions there is sufficient energy available to generate stimuli of required amplitude. When doing so the disadvantages shall be avoided associated to epiretinal implants of the kind discussed above and consisting mainly in that certain areas of the retina may not be used for stimulation because they are obscured by implant components.
SUMMARY OF THE INVENTION
These and other objects of the invention are solved by an implant of the kind mentioned above having a substrate with a first surface for applying same to a retina, wherein the substrate comprises electrodes for stimulating cells within the retina, the electrodes being provided on the surface and being exposed to visible light impinging on the retina such that stimuli are exerted on the cell by the electrodes, wherein, further, a first layer, being a photovoltaic layer responsive to non-visible light is provided and the stimuli are locally switched utilizing a voltage generated by the layer.
The object underlying the invention is thus entirely solved.
The invention makes use of the fact that for solving the object it is recommendable to effect the energy supply that is required for stimulation by infrared light. The optical elements as well as the retina of the human eye is permeable to infrared light. Therefore, even with sufficient high intensities no damage to the retina must be expected. The supply power being available within the eye may additionally be enhanced by effecting the infrared coupling on a global basis, i.e. over the maximum possible surface area of the retina or the implant, respectively, whereas the cells on the other hand side are exclusively stimulated locally.
In order to be independent from the available ambient light as well as from the physiological threshold of the retina with respect to visible light, non-visible light, preferably infrared light, is used for providing the required energy for generating the stimuli.
The power supply for the implant according to the present invention is, hence, independent from the available ambient light and is, further, independent of the fact whether the viewed image has a high or a low brightness.
In a preferred embodiment of the invention the electrodes, in a top plan view on the substrate, are surrounded by the photovoltaic layer.
This measure has the advantage that by setting the surface ratio between electrodes and photovoltaic layer accordingly, the surface area of the photovoltaic layer may be set in a predetermined manner. Preferably, the electrodes occupy a surface portion of between 10% and 50%.
In another preferred embodiment of the invention the electrodes comprise a switch adapted to be actuated optically and feeding through the voltage as the stimulus when being in a closed state.
This measure has the advantage that the implant generates the stimuli on exactly those points on the implant surface corresponding to the effectively viewed image.
In a first modification of this embodiment the switch is configured as an area in a second layer of the substrate, the second layer being electrically non-conductive when exposed to the non-visible light and being electrically conductive when exposed to the visible light.
This measure has the advantage that the electrode surface is exactly just as large as it corresponds to the bright, i.e. to the to-be-stimulated areas of the entire image. In all dark areas of the image in which no stimulation of the cells shall be effective, the non-visible light may be used for generating additional energy.
In this context it is further preferred in another embodiment of the invention to use amorphous, hydrogenized silicon (a-Si:H) as a material for the second layer. However, one may also use alloys of amorphous, hydrogenized silicon, for example alloys with carbon (a-SiC:H) o
Graf Heinz Gerhard
Graf Michael
Hierzenberger Anke
Nisch Wilfried
Schubert Markus B.
Eberhard-Karls-Universitat Tubingen Universitatsklinkum
Hamrick Claude A. S.
Manuel George
Oppenheimer Wolff & Donnelly LLP
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