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Methods for improving damaged retinal cell functionRelated Patent Categories: Surgery: Light, Thermal, And Electrical Application, Light, Thermal, And Electrical Application, Electrical Therapeutic Systems, Promoting Optical FunctionMethods for improving damaged retinal cell function description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060142818, Methods for improving damaged retinal cell function. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims the benefit of provisional application Ser. No. 60/301,877, entitled "METHOD OF IMPLANTING A RETINA STIMULATION DEVICE FOR GENERALIZED RETINAL ELECTRICAL STIMULATION", filed Jun. 26, 2001; Attorney reference no. 3614/62, and is hereby incorporated by reference in its entirety. FIELD OF THE INVENTION [0002] The present invention is directed to improving retinal cell visual function in partially damaged and/or degenerated retinas and also to protecting retinal cells from degeneration. BACKGROUND [0003] Many human retinal diseases cause vision loss by partial to complete destruction of the vascular layers of the eye that include the choroid and choriocapillaris, both of which nourish the outer anatomical retina and a portion of the inner anatomical retina of the eye. [0004] Many other retinal diseases cause vision loss due to partial to complete degeneration of one or both of the two anatomical retinal layers directly, due to inherent abnormalities of these layers. The components of the retinal layers include Bruch's membrane and retinal pigment epithelium which comprise the "outer anatomical retinal layer", and the photoreceptor, outer nuclear, outer plexiform, inner nuclear, inner plexiform, amacrine cell, ganglion cell and nerve fiber layers which comprise the "inner anatomical retinal layer", also known as the "neuroretina". The outer portion of the neuroretina is comprised of the photoreceptor and bipolar cell layers and is also known as the "outer retina" which is to be distinguished from the "outer anatomical retinal layer" as defined above. Loss of function of the outer retina is commonly the result of dysfunction of the outer anatomical retinal layer that provides nourishment to the outer retina and/or to direct defects of the outer retina itself. The final common result, however, is dysfunction of the outer retina that contains the light sensing cells, the photoreceptors. Some of these "outer retina" diseases include age-related macula degeneration, retinitis pigmentosa, choroidal disease, long-term retinal detachment, diabetic retinopathies, Stargardt's disease, choroideremia, Best's disease, and rupture of the choroid. The inner portion of the neuroretina, however, often remains functionally and anatomically quite intact and may be activated by the appropriate stimuli. [0005] While researchers have reported efforts to restore visual function in humans by transplanting a variety of retinal cells and retinal layers from donors to the subretinal space of recipients, no sustained visual improvement in such recipients has been widely accepted by the medical community. [0006] Multiple methods and devices to produce prosthetic artificial vision based on patterned electrical stimulation of the neuroretina in contact with, or in close proximity to, the source of electrical stimulation are known. These devices typically employ arrays of stimulating electrodes powered by photodiodes or microphotodiodes disposed on the epiretinal side (the surface of the retina facing the vitreous cavity) or the subretinal side (the underneath side) of the neuroretina. Such methods and implantable prosthetic electrical devices, designed to replace missing and damaged cells, are used to partially treat blindness in which the outer retinal cells have degenerated, but where the inner retinal layer is at least partially intact. Known devices typically employ arrays of stimulating electrodes powered by photodiodes or microphotodiodes (components that produce an electrical current or voltage potential in response to light) disposed on the epiretinal side or the subretinal side of the neuroretina. These devices can improve light perception. For example, subretinal implantation at discrete retinal locations has been shown to mimic light perception-mediated signaling; in one study (Chow and Chow, 1997), electrodes powered by external photodiodes were implanted in the subretinal space of adult rabbits. When the photodiodes, but not the rabbits' eyes themselves, were exposed to a flash of light, signaling in the brain visual cortex resembled that induced by light stimulation of the eyes. Further animal studies have demonstrated the safety and efficacy of such devices (Peachey and Chow, 1999). [0007] Examples of devices designed to be implanted predominantly subretinally include "Surface Electrode Microphotodiodes" (SEMCPs) (Chow, U.S. Pat. No. 5,024,223, 1991), Independent Surface Electrode Microphotodiodes (ISEMCPs and ISEMCP-Cs) (Chow and Chow, U.S. Pat. No. 5,397,350, 1995; Chow and Chow, U.S. Pat. No. 5,556,423, 1996), multi-phasic microphotodiode retinal implants (MMRIs, such as MMRI-4) (Chow and Chow, U.S. Pat. No. 5,895,415,1999), and VGMMRIs (Chow and Chow, U.S. application Ser. No. 09/539,399, 2000). All these devices can be generically called Silicon Retinal Prostheses (SRP). MMRIs and VGMMRIs are designed to be used by themselves alone, or with an externally worn adaptive imaging retinal stimulation system (AIRES). These implants effectively improve perception of light and dark. [0008] Cellular electrical signals also play important developmental roles, enabling nerve cells to develop and function properly. For example, nerve cells undergo constant remodeling, or "arborization", during development related to electric signaling. First an extensive preliminary network is formed that is then "pruned" and refined by mechanisms that include cell death, selective growth, loss of neurites (axonal and dendritic outgrowths), and the stabilization and elimination of synapses (Neely and Nicholls, 1995). If a neuron fails to exhibit or is inhibited from transducing normal electrical activity during arborization, axons fail to retract branches that had grown to inappropriate positions. [0009] The application of electric currents to organ systems other than the eye is known to promote and maintain certain cellular functions, including bone growth, spinal cord growth and cochlear spiral ganglion cell preservation (Acheson et al., 1991; Dooley et al., 1978; Evans et al., 2001; Kane, 1988; Koyama et al., 1997; Lagey et al., 1986; Leake et al., 1991; Leake et al., 1999; Politis and Zanakis, 1988a; Politis and Zanakis, 1988b; Politis and Zanakis, 1989; Politis et al., 1988a; Politis et al., 1988b). [0010] In other studies, the application of growth and neurotrophic-type factors was found to promote and maintain certain retinal cellular functions. For example, brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4), neurotrophin-5 (NT-5), fibroblastic growth factor (FGF) and glial cell line-derived neurotrophic factor (GDNF) have been shown to enhanced neurite outgrowth of retinal ganglion cells and to increase their survival in cell culture. GDNF has been shown to preserve rod photoreceptors in the rd/rd mouse, an animal model of retinal degeneration. Nerve growth factor (NGF) injected into the intra-ocular area of the C3H mouse, also a model of retinal degeneration, results in a significant increase of surviving photoreceptor cells compared to controls (Bosco and Linden, 1999; Caleo et al., 1999; Carmignoto et al., 1989; Cui et al., 1998; Frasson et al., 1999; Lambiase and Aloe, 1996; Reh et al., 1996). No methods or devices, however, to improve the general inherent visual function of damaged retinal cells distant from a source of electrical stimulation through the use of chronic electrical stimulation applied to the neuroretina from either within the eye or in direct contact with the outside of the eye are known. Also unknown is the application of growth or neurotrophic-type factors to further improve the ability of an electrical retina prosthesis that applies chronic electrical stimulation to the eye to improve retinal visual function. SUMMARY [0011] In one aspect, the invention provides a method of improving visual function that includes the perception of brightness in the presence of light, the perception of darkness in the absence of light, the perceptions of contrast, color, resolution, shape, motion, and visual field size of a damaged retina in a human eye by applying electrical stimulation to the damaged retina, eye or to both with a source of electrical stimulation wherein this electrical stimulation improves visual function of at least a portion of the damaged retina not in contact with the source of electrical stimulation. [0012] In another aspect, the invention provides methods of treating primary and secondary visual degradation resulting from a damaged retina by applying electrical stimulation to the eye with the damaged retina with a source of electrical stimulation, wherein a portion of the damaged retina not in contact with the source of electrical stimulation is treated. The damaged retina, for example, may comprise damaged photoreceptor cells, and such cells peripheral to the source of electrical stimulation exhibit improved visual function as a result of the electrical stimulation. [0013] Both of these aspects of the invention may have the following characteristics. Conditions that result in damaged retinas that may be treated with the various embodiments of the invention include age-related macular degeneration, retinitis pigmentosa, long-term retinal detachment, diabetic retinopathies, Stargardt's retinopathy, Leber's congenital amaurosis, Best's Disease, and choroidal disease or damage. Electrical stimulation may be, for example, provided to the retina or eye. Electrical sources include, e.g., a device or devices that contacts the eye or retina; when electrical stimulation is provided via this device or devices, at least a portion of the damaged retina distant, peripheral (or both) to the portion of the retina in contact with the device exhibits improved visual function. Suitable devices that provide electrical stimulation may have at least one photoactive surface (having one or more photodiodes) that is electrically connected to at least one stimulating electrode. Useful devices include Retinal Stimulation Devices (RSDs) comprising at least one of each: substrate, photoconductive/photovoltaic photodetector, such as a photodiode and/or related devices, stimulating electrode, and ground return electrode. RSDs may further comprise an electrical ground and an insulated conductor and a silicon tail. The substrate may also be fenestrated. The stimulating electrode of an RSD may be, for example, an anode or a cathode; the ground return electrode comprising an opposite polarity of the stimulating electrode. Examples of RSDs include ISEMCPs, ISEMCP-Cs and MMRIs. Electrical stimulation may be applied in response to light or may be applied intermittently in concert with or independently of light. The device may also comprise an inductive receiver and/or a solar cell, and/or a battery. The device may also comprise at least one electrode placed in contact with any portion of the eye and electrically connected to a source of stimulating current. Suitable locations of the eye for stimulation include, but are not limited to, the subretinal space, the epiretinal space, the subscleral space, the subconjunctival space, the vitreous cavity and the anterior chamber. Useful voltage potentials (V.sub.p's) of electrical stimulation are -20V.ltoreq.V.sub.p.ltoreq.+20V. [0014] In a further aspect, the invention provides a method of improving visual function in a damaged macula of a human eye by first selecting at least one device that is configured to generate an electrical current in response to light exposure; the device having at least one pixel; and implanting this device (or devices) in the subretinal space in a position that is peripheral to the macula. [0015] In another aspect, the invention provides a method of improving visual function by implanting a device in an eye of a patient having an outer neuroretina disease (such as age-related macular degeneration, retinitis pigmentosa, long-term retinal detachment, diabetic retinopathies, Stargardt's retinopathy, Leber's congenital amaurosis, Best's Disease or choroidal disease or injury), the method comprising selecting at least one device configured to generate an electrical current in response to exposure to a source of light, each of the at least one devices comprising at least one pixel; and implanting the device in a subretinal space in an eye of the patient having the outer retina disease, wherein the device is positioned in one of a peripheral and mid-peripheral region in the subretinal space outside of a macula of the eye. The device or devices may be implanted at a position in the subretinal space between about a 5.degree. and an 80.degree. angle off-axis from the macula, wherein the angle is defined by an intersection of an axis line extending from the macula to a central portion of the pupil and an off-axis line extending from the device to the central portion of the pupil. The device or devices may be implanted in any region of the retina, e.g. the temporal and/or nasal half retina region of the eye, or symmetrically around a region centered by the macula. [0016] In another aspect, the invention provides methods of implanting a device in a human eye, the method comprising implanting at least one device in one of a peripheral and mid-peripheral region in the subretinal space outside of the macula, wherein the device(s) is configured to generate an electrical current in response to exposure to a source of light, the device(s) comprising at least one pixel, and wherein the device is positioned away from a region of damaged retinal cells. [0017] In all aspects of the invention, the devices used in these methods to improve visual function of a damaged retina may be surgically implanted into the subretinal space at an angle between about 5.degree. and 80.degree. off-axis from a macula, wherein the angle is defined by an intersection of an axis line extending from the macula to a central portion of a pupil, and an off-axis line extending from the device to the central portion of the pupil. The device (with or without at least one fenestration) may be surgically implanted in at least one sector of a retina, excluding the macula. The device or devices may be implanted in the temporal or nasal (or both) half retina region of the eye, or symmetrically around a region centered by the macula. BRIEF DESCRIPTION OF THE DRAWINGS [0018] FIG. 1A presents top cross-section of a human eye. [0019] FIG. 1B presents a cross-section through the human eye that include the layers of the outer and inner anatomical retina, as indicated by the inset of FIG. 1A. [0020] FIG. 2A is a plan view of a preferred embodiment of RSD, showing the general plan structure of RSDs. Continue reading about Methods for improving damaged retinal cell function... 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