Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Retina
Reexamination Certificate
1998-07-29
2002-10-01
Manuel, George (Department: 3737)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Retina
Reexamination Certificate
active
06458157
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns an apparatus for electrical stimulation of physiologically excitable retinal nerve cells.
BACKGROUND OF THE INVENTION
The invention described is primarily for an implantable retinal stimulator or visual prosthesis or bionic eye or artificial eye. That is, a system of components designed for the restoration of some visual faculties to the profoundly blind or severely vision impaired. The main objectives of the invention is to restore the differentiation between light and dark and to offer some visual input from the environment.
In many patients who are blinded by degenerative conditions whereby the photoreceptors of the retina become dysfunctional, the retinal ganglion cells can remain largely in tact. It is the objective of the retinal -stimulator to by-pass the dysfunctional photoreceptors and electronically stimulate the surviving retinal ganglion cells, eventuating the perception of a spot of light or phosphene within the brain.
The invention described herein comprises an implanted receiver/decoder/stimulator connected to a multi site electrode array implanted on, near or under the surface of the retina. Through a tuned, inductive communication circuit, power and configuration data for the receiver/stimulator is obtained from an externally worn image processor/encoder/transmitter wherein images from the environment are obtained and processed into a grid of discreet sites of varying intensity and corresponding to the electrode sites of the array. Said intensities are then scaled in stimulus charge (amplitude x duration) in accordance with the individual patient comfort parameters such that the stimulus will be both useful, painless, and safe.
Understanding of the invention will be improved by an understanding of some of the anatomy and physiology of the human eye.
STRUCTURE OF THE HUMAN EYE
The majority of the human eye is protected within the orbital cavity. The exposed section is protected in a limited fashion by various appendages such as the eyelids and brow. Surrounded by the capsule of Tenon, a thin membrane which provides isolation and facilitates movement, the eyeball is embedded within the fatty media of the orbit.
The form of the globe itself is maintained by a hard, dense and unyielding fibrous membrane called the Sclerotic Coat (sclera). Its anterior surface is covered by the Conjunctiva, a membrane which provides the white colouring and is reflected to line the inner surface of the eyelids.
Forming approximately 15% of the anterior of the globe, the Cornea is a transparent quad layer structure consisting of epithelial cells (continuous with the conjunctiva), a central fibrous structure (Substantia Propria), an elastic lamina, and endothelial cells which line the anterior chamber. The cornea is a non vascular structure and is continuous with the sclera.
Approximately 85% of the posterior of the globe is comprised by the Choroid. A thin, highly vascular membrane, the choroid is loosely connected externally to the sclera and internally to the retina. At the point of exit of the optic nerve, the choroid is relatively thick in comparison to other sections and is firmly adhered to the sclera.
The Ciliary Body is comprised of the orbiculus ciliaris, ciliary processes and the ciliary muscle. It is primarily involved with the formation of aqueous humour and in adjusting the eye to the vision of near objects (accommodation).
The orbiculus ciliaris is continuous with the choroid. It is comprised of ridges which are arranged radially and is on the order of four millimetres in width.
The ciliary processes vary between 60 and 80 in number and are similar in structure to the choroid with the exception being that the vessels are larger and are primarily longitudinal in direction.
The ciliary muscle consists of two sets of fibres, circular and radial. By drawing upon the ciliary processes, this muscle contracts and thus relaxes the suspensory ligament of the lens causing the anterior surface of the lens to become more convex.
The Iris, (Latin for rainbow) so named from the various colours observed in different individuals, is a circular curtain which is suspended within the aqueous humour immediately behind the cornea. At its centre (slightly nasal to be precise) is the pupil, a circular aperture for the transmission of light, which changes in size with contractions of the iris. The circumference of the iris is continuous with the ciliary body and is connected to the cornea's elastic lamina by ligament.
The retina forms the interior surface of the eye from the fovea centralis which corresponds with the axis of the eye to the ora serrata near the ciliary body.
A highly complex structure, the retina consists of ten layers between the choroid at its outer surface and the vitreous humour at its inner surface. The ten layers are as follows:
Membrana limitans interna—the most internal layer, comprised of fibres known as the fibres of Muller.
Stratum opticum—a layer of nerve fibres formed by the expansion of the optic nerve.
Ganglionic layer—a single layer of retinal ganglion cells.
Inner molecular layer—a dense layer of fibrils which are interlaced with the dendrites of the ganglion cells and those of the inner nuclear layer (described below).
Inner nuclear layer—comprised of amnacrine, bipolar and horizontal cells.
Outer molecular layer—a dense layer (thinner than the inner molecular layer) of fibrils interlaced with the processes of the horizontal and bipolar cells of the previous layer and the bases of the rods and cones (described below).
Outer nuclear layer—comprised of clear oval nuclear bodies named the rod-granules and cone-granules. Rod-granules being the more populous.
Membrana limitans externa—similar to that of the membrana limitans interna, this layer is also comprised of fibres of Müller.
Jacob's Membrane—the layer of rods and cones. These are the photoreceptors and will be described in more detail later.
Tapetum nigrum—a single layer of hexagonal epithelial cells containing pigment-granules.
Optical or Refracting Media:
Little more than water (with some small amounts of Na and Cl), aqueous humour fills the anterior chamber (bounded by the back of the cornea and the front of the iris) and the posterior chamber (bounded by the back of the iris, the ciliary body and the lens) of the eye.
Filling approximately 80% of the volume of the eye, the vitreous body is perfectly transparent. Bound within a thin and delicate membrane (membrana hyaloidea), the vitreous body is believed to be comprised of numerous laminations of nearly pure water with small amounts of salts and albumen. It is bounded by the retina, the ciliary body and the lens.
The lens is a transparent body consisting of concentric layers ranging from soft on the surface to firm towards the centre. Surrounded by a brittle but highly elastic membrane, the lens is approximately 10 mm in diameter and 4 mm in thickness.
PHYSIOLOGY OF THE HUMAN EYE
The function of the non-retinal components of the ocular anatomy is to maintain a focused, clear image of visual stimuli fixed on the surface of the retina. As the mechanisms involved in this process are analogous to that of a photographic camera, comparisons shall be made for illustrative purposes.
Light enters the eye at the anterior surface of the cornea. It acts in much the same way as the lens of a photographic camera. Approximately two-thirds of the bending of light necessary for providing focus takes place at the air-cornea interface.
Richly supplied with nerves, the cornea is highly sensitive to touch and pain. Its cleanliness is maintained by the tear gland secretion of lubricating fluid which is swept across the surface by the eyelids. This cleaning mechanism is amplified by the presence of dust particles or other foreign objects whereby a reflex leads to blinking and the secretion of additional lubricant.
While the lens provides light bending power in addition to the cornea, its primary role is distance compensation required to maintain focus on the retinal surface. Similar to adjusting focus of a camer
Alston & Bird LLP
Manuel George
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