Note: Descriptions are shown in the official language in which they were submitted.
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VISUAL PROSTHESIS
This is a divisional application of Canadian Patent
Application Serial No. 2,323,550 filed on March 11, 1999.
Technical Field Of The Invention
This invention relates to medical ocular devices and
methods, and more particularly to intraocular electrical
retinal stimulation for phosphene generation in a visual
prosthesis device and method of using same. It should be
understood that the expression "the invention" and the like
encompasses the subject matter of both the parent and the
divisional applications.
Background of The Invention
In 1755 LeRoy passed the discharge of a Leyden jar
through the orbit of a man who was blind from cataract and
the patient saw "flames passing rapidly downwards." Ever
since, there has been a fascination with electrically
elicited visual perception. The general concepts of
electrical stimulation of retinal cells to produce these
flashes of light or phosphenes has been known for quite some
time. Based on these general principles, some early attempts
at devising a prosthesis for aiding the visually impaired
have included attaching electrodes to the head or eyelids of
patients. While some of these early attempts met with some
limited success, these early prosthesis devices were large,
bulky and could not produce adequate simulated vision to
truly aid the visually impaired.
As intraocular surgical techniques advanced, however, it
became possible to apply a more focused stimulation on small
groups and even on individual retinal cells to generate
focused phosphenes through devices implanted within the eye
itself. This has sparked renewed interest in developing
methods and apparatuses to aid the visually impaired.
Specifically, great effort has been expended in the area of
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intraocular retinal prosthesis devices in an effort to restore
vision in cases where blindness is caused by photoreceptor
degenerative retinal diseases such as retinitis pigmentosa and
age related macular degeneration which affect millions of
people worldwide.
One such device is described in U.S. Patent No.
4,628,933, issued to Michelson on December 16, 1986, for a
METHOD AND APPARATUS FOR VISUAL PROSTHESIS. The Michelson
'933 apparatus includes an array of photosensitive devices on
its surface which are connected to a plurality of electrodes
positioned on the opposite surface of the device to stimulate
the retina. These electrodes are disposed to form an array
similar to a "bed of nails" having conductors which impinge
directly on the retina to stimulate the retinal cells. The
Michelson '933 device is powered by a separate circuit
through electromagnetic or radio frequency induction. To
receive this energy, an inductor is included with the
Michelson '933 device either wound on the periphery of the
device or formed on one of the surfaces through
photolithographic circuit techniques. The induced signal is
then rectified and filtered to power the circuit elements.
Such a device, however, increases the possibility of
retinal trauma by the use of its "bed of nails" type electrodes
which impinge directly on the retinal tissue. Additionally,
by including the photosensitive elements integral with the
implanted device within the eye, the processing of the
perceived image is quite limited. It is first limited by the
quality of the lens of the patient's eye and her ability to
focus that lens. If the lens is occluded by cataracts or
otherwise not clear, it will need to be replaced to allow
proper operation of the prosthesis. Likewise, prescription
glasses or contact lenses may be required to focus the
image on the prosthesis for patients who would otherwise
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be near or far sighted.
The Michelson `933 device is also limited by the
physical size available within the ocular cavity. Since
this cavity is small and since the device must be
supported by the retinal tissue itself, the amount of
image processing circuitry which can be included therein
is limited. Furthermore, the amount of image processing
circuitry is also limited by the power availability and
utilization requirements within the ocular cavity. As=a
result of these limiting factors, the Michelson 1933
device does not include any image processing circuitry
other than common signal amplifiers which simply tune
the responses to the frequency response bandwidth of the
retinal neurons, to shape the output waveform in a
charge-balanced square wave, and trim the voltage and
current output to acceptable levels for the neurons.
Brief Summary Of The Invention
In view of the above, it is therefore an object of
the instant invention to overcome at least some of these
and other known problems existing in the art. More
particularly, it is an object of the instant invention
to provide a new and improved visual prosthesis.
Specifically, it is an object of the instant invention
to provide a visual prosthesis which will at least
partially restore vision in cases where blindness is
caused by photoreceptor degenerative retinal diseases.
It is a further objective of the instant invention to
provide a visual prosthesis which provides a level of
functional vision which will improve a patient's
mobility and enable reading. Additionally, it is an
object of the instant invention to provide such a visual
prosthesis which can be worn during routine daily
activities and which is aesthetically acceptable to the
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patient. Furthermore, it is an object of the instant
invention to provide a method of restoring vision.
In view of these objectives, it is a feature of the
visual prosthesis of the instant invention to provide
both intra-ocular and extra-ocular components to
maximize the visual quality produced and minimize the
retinal effect caused by the visual prosthesis. It is a
further feature of the instant invention to provide a
means of transmitting the visual signal of the perceived
environment from the extra-ocular components to the
intra-ocular components without physical contact
therebetween. Additionally, it is a feature of the
instant invention to extract the required power for the
intra-ocular components from the visual signal without
the need for a separate power signal transmission.
Furthermore, it is a feature of the instant invention to
provide a visual prosthesis whose intra-ocular
electrodes do not pierce the retina.
Therefore, in accordance with the above objectives
and features, it is an aspect of the instant invention
to provide a visual prosthesis having an extra-ocular
image capturing and encoding element, and a radio
frequency based transmission element. It is a further
aspect of the instant invention to provide an intra-
ocular stimulating electrode on the surface of the
retina. In accordance with another aspect of the
instant invention, a radio frequency receiving,
decoding, and demultiplexing element is provided to
receive the radio frequency transmitted visual signals.
An aspect of one embodiment of the instant invention
includes providing the radio frequency receiving,
decoding, and demultiplexing element intra-ocular, while
another aspect of another embodiment includes providing
the radio frequency receiving, decoding, and
demultiplexing element extra-ocular.
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In one embodiment, the present invention provides a
visual prosthesis, comprising:
(a) retinal tissue stimulation means comprising an
electrode array configured to stimulate retinal cells to
5 produce phosphenes in a pattern to stimulate vision;
(b) a circuit block on the body of a user outside the wall
of the sclera; and
(c) an electrical cable or wire piercing the sclera and
connecting said circuit block to said retinal tissue
stimulation means.
An embodiment of the visual prosthesis of the instant
invention comprises a camera for converting a visual image
to electrical impulses, image sampling circuitry for
selecting an image at a given point in time, and encoder
circuitry for encoding the selected image to allow a
pixelized display of it. A signal corresponding to the
selected image is then used to modulate a radio frequency
carrier signal so that it can be transmitted into the eye by
a tuned coil pair having a primary and a secondary coil.
A demodulator circuit is coupled to the secondary coil
for extracting the visual signal output from the radio
frequency carrier signal. A decoder is coupled to the
demodulator for decoding the visual signal output into a
plurality of individual stimulation control signals which
are coupled to current generation circuitry which generates
stimulation current signals in response. An electrode array
has a plurality of electrodes which are operatively coupled
to the current generation circuitry means. The electrodes
stimulate the retinal tissue in response to these individual
stimulation control signals.
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5a
A method of at least partially restoring vision to
users who suffer from photoreceptor degenerative retinal
conditions of the eye is included and comprises the steps
of: a) perceiving a visual image and producing a visual
signal output in response thereto; b) wirelessly
transmitting the visual signal output into the eye; and c)
stimulating retinal tissue of the user in accordance with
the visual signal output.
These and other aims, objectives, and advantages of the
invention will become more apparent from the following
detailed description while taken into conjunction with the
accompanying drawings.
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Brief Description Of The Drawings
FIG. 1 is a simplified schematic block diagram of a
visual prosthesis in accordance with an embodiment of
the instant invention;
FIG. 2 is an expanded schematic block diagram of
visual acquiring, encoding, and radio frequency
transmission components of an embodiment of the visual
prosthesis of the instant invention;
FIG. 3 is an expanded schematic block diagram of
radio frequency visual signal receiving, decoding, and
retinal stimulation components of an embodiment of the
visual prosthesis of the instant invention;
FIG. 4 is a simplified cross-sectional view of an
embodiment of the visual prosthesis of the instant
invention as implanted within the eye;
FIG. 5 is a simplified cross-sectional view of an
alternate embodiment of the visual prosthesis of the
instant invention as implanted within the eye;
FIG. 6 is a simplified cross-sectional view of a
further alternate embodiment of the visual prosthesis of
the instant invention as implanted within the eye;
FIG. 7 is a simplified schematic view of an intra-
ocular stimulation electrode array in accordance with an
aspect of an embodiment of the visual prosthesis of the
instant invention;
FIG. 8 is a partial schematic view of a section of
an intra-ocular stimulation electrode array illustrating
attachment details thereof in accordance with an aspect
of an embodiment of the visual prosthesis of the instant
invention;
FIG. 9 is a partial schematic view of a section of
an intra-ocular stimulation electrode array illustrating
attachment details thereof in accordance with an aspect
of an alternative embodiment of the visual prosthesis of
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the instant invention; and
FIG. 10 is a partial schematic view of a section of
an intra-ocular stimulation electrode array illustrating
attachment details thereof in accordance with an-aspect
of a further alternative embodiment of the visual
prosthesis of the instant invention.
While the invention is susceptible of various
modifications and alternative constructions, certain
illustrative embodiments thereof have been shown in the
drawings and will be described below in detail.. It
should be understood, however, that there is no
intention to limit the invention to the specific forms
disclosed, but on the contrary, the intention is to
cover all modifications, alternative constructions,
methods, and equivalents falling within the spirit and
scope of the invention as defined by the appended
claims.
Detailed Description Of The Preferred Embodiment
As discussed briefly above, the apparatus of the
instant invention is a medical device which will at
least partially restore vision in cases where blindness
is caused by photoreceptor degenerative retinal diseases
such as retinitis pigmentosa and age related macular
degeneration which affect millions of people worldwide.
The partial restoration of vision is intended to improve
the patient's mobility and enable at least large print
reading, and thus provide an increased sense of
independence. Briefly, visual perception is achieved by
converting an image of the scene before the patient into
a series of electrical pulses that are mapped onto the
retina by electrically stimulating the viable nerve
cells beyond the dysfunctional photoreceptors. It is
therefore a goal of the instant invention to provide a
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level of functional vision in a package that can be worn
during routine daily activities and is aesthetically
acceptable to the patient. The entire system of the
instant invention is contained in a portable body worn
package which functions without the use of implanted
batteries or connector penetrations of the eye. The
intraocular portions of the visual prosthesis of the
instant invention are designed to be implanted in the
patient's eye using standard ophthalmic surgical
techniques.
Specifically, therefore, a visual prosthesis in
accordance with a preferred embodiment of the instant
invention comprises a means for perceiving a visual
image which produces a visual signal output in response
thereto, a retinal tissue stimulation means adapted to
be operatively attached to a retina of a user, and a
wireless visual signal communication means for
transmitting the visual signal output to the retinal
tissue stimulation means. Preferably, the means for
perceiving a visual image comprises a camera means for
converting a visual image to electrical impulses, image
sampling means coupled to the camera means for selecting
an image at a given point in time, and encoder means
coupled to the image sampling means for encoding the
selected image to allow a pixelized display thereof.
Additionally, in a preferred embodiment of the
instant invention, the retinal tissue stimulation means
comprises a decoder means responsive to the visual
signal output for decoding the visual signal output into
a plurality of individual stimulation control signals,
current generation circuitry means coupled to the
decoder means and responsive to the plurality of
individual stimulation control signals for generating
stimulation current signals, and an electrode array
having a plurality of electrodes operatively coupled to
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the current generation circuitry means. These
electrodes are responsive to the individual stimulation
control signals, and generate stimulation pulses
sufficient to stimulate retinal tissue.
Furthermore, in a preferred embodiment of the
instant invention, the electrode array further comprises
attachment means adapted for attaching the electrode
array to the retina of a user. In an embodiment, the
electrode array defines at least one mounting aperture
therein, and the attachment means comprises at least one
retinal tack positioned within the at least one mounting
aperture. Alternatively, the electrode array includes
an outer surface edge defining at least two scalloped
portions therein, and the attachment means comprises a
retinal tack positioned within each of the scalloped
portions. In a further alternate embodiment, the
electrode array includes at least a first magnet
attached thereto, and the attachment means comprises a
second magnet adapted to be attached on the outside of
the sclera of a user opposite a desired point of
attachment of the electrode array on the retina. In yet
a further embodiment, the attachment means comprises
adhesive placed on a surface of said electrode array to
be attached to the retina.
In a further embodiment of the instant invention,
the wireless visual signal communication means comprises
a carrier generator means for generating a radio
frequency carrier signal, a modulator means responsive
to the radio frequency carrier signal and to the visual
signal output for modulating the radio frequency carrier
signal by the visual signal output, producing a radio
frequency modulated image signal. Additionally, this
embodiment includes a tuned coil pair having a primary
and a secondary coil. The primary coil is operatively
coupled to the modulator means to transmit the radio
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frequency modulated image signal. The secondary coil is
tuned to receive the radio frequency modulated image
signal. A demodulator means is coupled to the secondary
coil for extracting the visual signal output from the
5 radio frequency carrier signal.
A preferred embodiment of the instant invention
further comprising power supply means coupled to the
secondary coil for powering the retinal tissue
stimulation means and the demodulator means. This is
10 accomplished preferably by extracting energy from the
radio frequency modulated image signal. The power
supply means rectifies the radio frequency carrier
signal from the radio frequency modulated image signal
received by said secondary coil to produce the dc power
output to power the retinal tissue stimulation means and
the demodulator means.
A preferred method of at least partially restoring
vision to users who suffer from photoreceptor
degenerative retinal conditions of the eye, therefore,
comprises the steps of perceiving a visual image and
producing a visual signal output in response thereto,
wirelessly transmitting the visual signal output into
the eye, and stimulating retinal tissue of the user in
accordance with the visual signal output. Preferably,
the step of perceiving a visual image and producing a
visual signal output in response thereto comprises the
steps of converting a visual image to electrical
impulses, sampling the electrical impulses corresponding
to an image at a given point in time, and encoding the
selected image to allow a pixelized display thereof.
Additionally, preferably the step of wirelessly
transmitting the visual signal output into the eye
comprises the steps of generating a radio frequency
carrier signal, modulating the radio frequency carrier
signal by the visual signal output to produce a radio
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frequency modulated image signal, transmitting the radio
frequency modulated image signal, receiving the radio
frequency modulated image signal, and extracting the
visual signal output from the radio frequency carrier
signal. Moreover, in a preferred embodiment the step of
stimulating retinal tissue of the user in accordance
with the visual signal output comprises the steps of
decoding the visual signal output into a plurality of
individual stimulation control signals, generating
stimulation current signals, and applying stimulation to
the retinal tissue in accordance with the stimulation
current signals.
In an exemplary embodiment of the above described
invention illustrated in block diagram form in FIG. 1, a
visual prosthetic device, illustrated as retinal
prosthesis 10, includes an image capturing element, such
as a standard charge coupled device (CCD) camera 12,
whose visual signal output is processed and encoded in
circuit block 14. This processed and encoded image
signal is then transmitted via primary coil 16 as a
radio frequency encoded image signal. A secondary coil
18 receives the radio frequency encoded image signal and
passes it to the decoding and demultiplexing circuit
block 20. This circuit block 20 then communicates the
decoded image signal to an electrode array 22 which
stimulates the retinal cells to produce phosphenes in a
pattern to simulate vision.
It should be noted that the dashed line 24 in FIG.
1 is included to separate the image acquiring and
transmitting portion 26 from the image receiving and
stimulation portion 28 of the visual retinal prosthesis
10, and may or may not indicate the separation of the
extra-ocular region from the intra-ocular region as will
be described more fully below with reference to FIGs. 4-
6. It should also be noted that while the figures
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illustrate the use of a CCD camera, the scope of the
invention is not so limited but includes other
technologies of image acquisition equipment such as
video cameras, digital cameras, CMOS cameras, etc.
The image acquiring and transmitting portion. 26 of
the visual prosthesis of the instant invention is
illustrated in greater detail in FIG. 2, and reference
is now made thereto. As may be observed from this
figure, the image signal captured by the camera 12 is
output to an image sampler circuit 30, and this sampled
image is passed to the pixel encoder 32. Once this
sampled image signal is properly encoded, it is passed
to the signal modulator 34 which uses it to modulate a
radio frequency carrier signal generated by the carrier
generator 36. This radio frequency modulated image
signal is then transmitted via the primary coil 16.
The encoding scheme is optimized for the target
image resolution which is determined by the size of the
implanted electrode array, as discussed more fully
below. The encoded information includes such parameters
as the magnitude, timing, and sequence of the
stimulation pulses which will be generated by the array
to simulate the image through retinal stimulation. The
modulation technique is consistent with the data rate,
and maximizes the fidelity of the recovered information
over the intended transmission path.
The radio frequency modulated image signal is
received by the image receiving and stimulation portion
28 of the visual prosthesis, as illustrated in greater
detail in FIG. 3. Once this signal is received by the
secondary coil 18, it is passed to the demodulator 38
where the carrier signal is removed from the encoded
image signal. The encoded image signal is then.passed
to a decoder/demultiplexer 40 which in turn outputs the
image information to a current generator 42 which drives
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the individual electrodes of the electrode array 22.
The electric power for this image receiving and
stimulation portion 28 of the visual prosthesis is
derived from the energy contained in the carrier-..:Signal
through rectifier 44. This carrier signal is rectified
to provide the direct current to power the implanted
electronics and generate the stimulation pulses. In
this way a separate power transmission signal is not
required.
The image receiving and stimulation portion 28 of
the visual prosthesis serves to demodulate and decode
the stimulation information and generate the proper
stimulation pulses which are transmitted to the
electrode array 22 implanted on the retina. The decoded
transmission is used to determine the characteristics of
the stimulation pulse and where this pulse is applied on
the electrode array 22. The pulses are transferred by
means of a miniature ribbon cable 46 that lies within
the intraocular cavity, or by other appropriate means
such as, for example, fiberoptic cable.
One embodiment of the physical implantation of the
visual prosthesis of the instant invention is
illustrated in FIG. 4 to which reference is now made.
As discussed above, the primary coil 16 is used to
transmit the radio frequency encoded image signal to the
secondary coil 18. This primary coil is located
preferably either in an eyeglass lens, frame, or in a
soft contact lens. This coil 16 is used to inductively
couple the radio frequency encoded image signal to the
secondary coil 18 which, in this embodiment, is
implanted behind the iris 48. This secondary coil 18 is
coupled to and collocated with the decoding/
demultiplexing circuitry 20. The small ribbon cable 46
is located along the interior wall of the eye and
couples the circuitry 20 to the electrode array 22 which
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is placed on the retina 50 near the fovea 52.
Alternatively, the circuitry 20 can be integrated with
the electrode array 22, in which case only a small wire
from the secondary coil 18 is needed to couple the
visual signal to the combined circuitry and array, (not
illustrated). The details of the attachment mechanisms
for securing the electrode array 22 to the retina 50
will be described in detail below with reference to
FIGs. 8-10.
In an alternate embodiment of the instant invention
illustrated in FIG. 5, the decoding/demultiplexing
circuitry 20 is no longer collocated with the secondary
coil 18 behind the iris 48, but is instead attached to
the outside of the sclera 54. The attachment may be by
suturing or other appropriate means. In this embodiment
the decoding/demultiplexing circuitry 20 is placed in a
hermetically sealed package and is coupled to the
secondary coil by a small wire 56 which pierces the
sclera 54. The small ribbon cable 46 coupling the
decoding/demultiplexing circuitry 20 to the electrode
array 22 mounted on the retina 50 also pierces the
sclera 54.
In a further alternate embodiment of the instant
invention, as illustrated in FIG. 6, the secondary coil
may also be attached to the sclera 54 instead of being
implanted within the eye. As with the decoding/
demultiplexing circuitry 20, the attachment of the
secondary coil 18 to the sclera 54 may be by suturing or
other appropriate means. In this way, only the small
ribbon cable 46 which attaches the decoding/
demultiplexing circuitry 20 to the electrode array 22
mounted on the retina 50 is required to pierce the
sclera 54. The extra-ocular attachment of the decoding/
demultiplexing circuitry 20 allows increased access to
this circuitry which eases the replacement or updating
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of these components.
As discussed above, the electrode array 22,
illustrated schematically in FIG. 7, is a biocompatible
device which is mounted onto the surface of the retina
5 near the fovea. This array 22 can either be a passive
element that only serves to transfer the charge in the
stimulation pulses to the retinal tissue, or an active
network that can control the selection of the
stimulation sites using information encoded in its
10 input. The stimulation sites 58 in the array are spaced
to provide a level of visual acuity consistent with the
ability of the patient to discriminate the activation of
adjacent sites. The stimulation sites 58 are composed
of a material designed to maximize the transfer of
15 charge between the electrode and the surrounding tissue.
While the array 22 illustrated in FIG. 7 has only a 5X5
array of stimulation sites, this number may be increased
or decreased. If the size of the array 22 increases, it
is preferable that the array 22 be flexible to allow
surface contact with all appropriate areas of the
retina. An electrode design which is compatible with
electrode array 22 of the instant invention is disclosed
in U.S. Patent No. 5,109,844, issued to de Juan, Jr. et
al. on May 5, 1992, for RETINAL MICROSTIMULATION.
The attachment of the electrode array to the
surface of the retina is accomplished using any suitable
method. In one embodiment illustrated in FIG. 8, a
mechanical fixation device, such as titanium tack 60
commonly employed to aid in retinal re-attachment by
holding the detached section of retina against the
choroid, is used. The tack 60 is passed through a
circular hole 62 in each corner of the body of the array
22 and holds the array in place by piercing the retina,
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choroid, and sclera. As an alternative to the tack 60,
suturing may also serve as the mechanical fixation
device.
In an alternate embodiment, as illustrated in FIG.
9, the array may be secured to the retina by placing the
tack 60 into a scalloped portion illustrated as a
semicircular notch 64 in each corner of the array 22,
and the resulting compression of the array 22 holds it.
in place. This method of attachment offers the
advantage of easier replacement since the tack 60 does
not penetrate the body of the array.
A less intrusive alternate method of attaching the
array 22 to the retina is illustrated in the alternate
embodiment of FIG. 10. This embodiment utilizes inert
miniature rare earth magnets 66 which are embedded into
each corner of the silicone array 22 during casting. A
second set of magnets (not shown) are sewn onto the
outside of the eye directly across from the desired
position of the array 22. The magnetic attraction
between the intraocular magnets 66 in the array 22 and
the magnets sewn on the outside of the eye serves to
hold the array 22 in place. This method obviates the
need to pierce the eye wall with a tack and allows for
easier replacement of the array.
An alternate embodiment of the instant invention
utilizes a medically approved adhesive, such as
cyanoacrylate or other appropriate adhesive, to secure
the array to the retina. In this embodiment, the
adhesive is applied to the edges of the array prior to
its final placement on the retina. A temporary air
pocket is then created in the vitreous to allow the
adhesive to cure.
In a preferred embodiment of the visual prosthesis
of the instant invention, the materials utilized in the
components which are part of the retinal implant are
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those used in current day cochlear implants. It should
be noted, however, that designation of such materials
does not limit the scope of the invention as other,
possibly better and more. appropriate materials may be
approved for intraocular implantation. In a preferred
embodiment, the packaging for the implanted electronics
is preferably titanium covered by silicone. The
secondary coil is preferably made of platinum and also
embedded in silicone. In this embodiment the electrode
array is preferably composed of platinum wires within a
silicone matrix. All of these materials have been
approved by the FDA for intraocular use and exhibit
proper electrical and biological characteristics for use
in such a visual prosthesis.
Numerous modifications and alternative embodiments
of the invention will be apparent to those skilled in
the art in view of the foregoing description.
Accordingly, this description is to be construed as
illustrative only and is for the purpose of teaching
those skilled in the art the best mode for carrying out
the invention. The details of the structure and
architecture may be varied substantially without
departing from the spirit of the invention, and the
exclusive use of all modifications which come within the
scope of the appended claims is reserved-
