1. Field of the Invention
The present invention relates to prismatic intraocular devices and related methods and systems for using such devices to improve, and more desirably restore vision. In a particularly preferred embodiment, the devices and related methods and systems are useful for patients having central field vision loss, such as encountered with degenerative retinal conditions, including but not limited to age-related macular degeneration, diabetic macular edema, lebers optic neuropathy, myopic macular degeneration, retinitis pigmentosa, and the like. In another preferred embodiment, the devices and related methods and systems are useful for patients having binocular misalignment, such as esotropia, exotropia, and vertical imbalances.
2. Description of the Related Art
Retinal degenerative conditions (RDCs) adversely affect eyesight and often lead to partial or complete blindness. An RDC such as macular degeneration leaves the afflicted individual with “blind spot” or scotoma usually at or near the center of a person's visual field. The blind spot or scotoma may appear as a black, gray, or distorted image. Objects in the central field of vision falling within the scotoma are not visible, thus permitting the afflicted individual to view only peripheral images around the blind spot. The visual field provided by such peripheral images is often insufficient to allow the individual to perform routine activities such as reading, driving a vehicle, or even daily chores and errands. For example, when an individual having a RDC attempts to recognize another person at a distance, the individual may be able to discern the eccentric body portions of the viewed person peripherally, but the scotoma may “wipe out” the facial details of the viewed person, rendering the person unrecognizable.
To understand RDCs, it is necessary to have a basic understanding of the human eye and the afflictions that lead to RDCs. Generally, the most outwardly visible structures of the human eye include an optically clear anterior cornea, the iris sphincter sitting behind the cornea, and the pupil, which is an aperture defined by the inner rim of the iris. The pupil appears as a circular opening concentrically inward of the iris. A physiological crystalline lens in a capsular bag is positioned posterior to the iris. Ciliary muscle concentrically surrounds the capsular bag, and is coupled to the physiological crystalline lens by suspensory ligaments, also known as zonules. The chamber between the posterior cornea and the front surface of the capsular bag is commonly referred to in the art as the anterior chamber, which contains a fluid known as the aqueous humor. A posterior chamber, filled with vitreous humor, is behind the anterior chamber, and includes the capsular bag and the physiological crystalline lens.
Light entering the eye through the cornea is converged by the crystalline lens towards the retina, and more particular to a central part of the retina known as the macula, arriving at a point focus known as the fovea. The cornea and tear film are responsible for the initial convergence of entering light. Subsequent to refraction by the cornea, the light passes through the physiological crystalline lens, where the light is refracted again. When focusing on an object, ideally the physiological crystalline lens refracts incoming light towards a point image on the fovea of the retina. The amount of bending to which the light is subjected is termed the refractive power. Generally, an RDC involves damage to the fovea, and can spread into the macula. In most patients, even in those with advanced macular degeneration, the macula is not completely damaged, but retains healthy or functional areas.
The person who suffers from a RDC is typically treated optically by using magnification or prism in lens form. At distance, a Galilean telescopic magnifying device may be placed in front of the eye or in the eye and customized to the user's needs. The magnification of the device enlarges the image viewed, expanding the image into more healthy areas of retina peripheral (eccentric) to the scotoma. At near, the person suffering from a RDC usually needs magnification in the form of magnifying plus powered lenses and/or prisms—the former (i.e., the plus lenses and magnifiers) to help enlarge the image outside of the scotoma as in the telescopic example and the latter (e.g., the prisms) to help shift the images to different, more functional areas of the retina.
The prismatic lens approach typically involves mounting a prism in an eyeglass frame. The prism is designed to redirect incoming or incident light rays, thereby angling the departing rays into healthy or functional portions of the retina. Angling the light rays in this manner shifts the scotoma out of the visual line of sight. It has been theorized to place a prism in an intraocular lens replacing the natural or physiological lens of the eye. Examples of theoretical, implantable prismatic lens devices are found in U.S. Pat. Nos. 5,728,156, 5,683,457, and 4,581,031, which disclose using prism wedges for shifting light away from the diseased center of the retina to a functional portion, and purportedly thereby restoring the central field vision to a patient.
The addition of a prism wedge to an intraocular lens would increase the overall thickness of the optic. The thickness of the prism wedges of such theoretical devices would need to be sufficient to permit redirection of the image a sufficient distance (or diopter) away from the damaged portion of the macular, to a healthy area of the retina. However, the relatively large thickness required of an intraocular prism to attain such an image shift would be problematic in several respects. Implantation of a thick prism carries certain surgical risk. During implantation of a thick prism-containing lens, the capsular bag intended to hold the lens would be susceptible to breakage and tearing, which would necessitate removal of the lens and vitrectomy and create risk of ultimately more macular damage. Further, the insertion incision for creating an opening to receive a thick prism-containing lens would be larger than required with a thinner prism-containing lens. Another drawback is a thick prism lens would preclude a second device from being implanted in the capsular bag to enhance magnification and/or allow for minification, such as in the case of creating a Galilean telescopic effect.
Another visual defect afflicting a large segment of the population is known generally as strabismus or binocular misalignment. A person's processing of viewed three-dimensional objects depends on proper alignment of the eyes. When both eyes are properly aligned and targeted on the same object, a single object is viewed. On the other hand, when one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain, causing loss of depth perception and binocular vision.
Strabismus, more commonly referred to as cross-eye, generally is characterized by a misalignment of the eyes. Esotropia, the most common form of strabismus, involves deviations in which the eyes are misaligned inwards, and more specifically one eye deviates inward while the other fixates normally. With esotropia, visual axes are turned inward so that they cross when focused on distance objects. (The visual axis is described as the axis of the eye that extends directly outward from the macula through the visual axis of the cornea towards optical infinity.) Another form of strabismus known as exotropia involves a condition in which one eye deviates outward so that the eyes do not cross when focused on distant objects.
Binocular function is commonly restored in patients with strabismus using prismatic lenses designed to realign images toward the binocular retinal locus. For example, eso-deviations as corrected by placing eyeglasses with a “base-in” prism lens in front of the eye. Exo-deviations are corrected by placing eyeglass with a “base-out” prism lens in front of one or both of the eyes. Vertical deviations, where the plane(s) of one or both eyes are not aligned in the vertical direction, are corrected with “base-up” or “base-down” prism(s) in the eyeglasses. A drawback of these conventional solutions is that the user becomes dependent upon eyeglasses.