The prior art is replete with innovations in contact lens designs. One such innovation is the rigid gas permeable (RGP) contact lens. This optical device has been successfully used in corneal lens to provide visual corrections of hyperopia, presbyopia, and myopia. The lenses have also been used for limited corneal molding. Examples of such applications are described in U.S. Pat. Nos. 4,952,045, 5,192,365 and 5,349,395 issued to Nick Stoyan. Many disadvantages still exist, however, with conventional contact lens designs. Corneal lens, for example, are generally prone to dislodgement from the eye if the wearer is subjected to sharp changes in motion, as often encountered during participation in sports and other physical activities. Dislodging of the lens can be both uncomfortable and dangerous.
Another type of lens is the scleral contact lens. A scleral lens covers most of the sclera and all of the cornea of the eye. Additionally, the scleral lens is wholly supported by the scleral portion of the eye and vaults the cornea to provide a cavity for tears or a tear substitute. These lenses have been conventionally formed of blown glass and have been relatively thick, being on the order of 2.0 to 3.0 mm thick. The concave, or posterior, surface of the lenses had two primary areas of curvature, the first being an outer peripheral area that approximated the scleral curvature, and the other being a central curved area that vaulted the cornea by as much as 2.0 mm providing a chamber that was filled with a tear substitute. The convex, or anterior, surface of the lens had a contour approximating that of the inner surface except in the center which was ground to provide optical correction. In addition to being thick, scleral lenses are also relatively large, having a typical diameter of about 25 mm, often causing eye irritation if worn for more than several hours.
Prior art scleral contact lenses have also been manufactured of plastic materials based on a casting of the eye. In this arrangement, the center of the lens has minimal vaulting and does not require a tear substitute. However, the diameter and thickness of the lens is virtually the same as the above mentioned glass, and similar glass-plastic composite lenses.
Plastic scleral contact lenses were also produced by lathing and polishing a plastic preform. The concave surface contained at least two, and as many as 10, curves to approximate the shape of the eye. These designs produced a relatively thinner lens (albeit still very thick by today's standards) with little or no clearance in the scleral area and little to extreme clearance in the corneal area. While some of the above designs were considered improvements over earlier lenses, the ability to wear scleral contact lenses has, heretofore, been very limited, both as to wearing time and in the number of patients able to tolerate them.
One attempt to provide a smaller diameter contact lens is described in U.S. Pat. No. 4,194,815 issued Mar. 25, 1980 to Wayne E. Trombley for a SEMI-SCLERAL CONTACT LENS. The Trombley lens is aligned with, i.e., contacts, the central corneal area of an eye, then vaults the limbus and a portion of the scleral area of the eye before coming down and making contact, at the very outer peripheral area of the lens, with the sclera. Thus, the Trombley lens vaults all of the eye area between the central cornea and a point contact line on the sclera. If formed of a rigid material, a possibility suggested by Trombley, the very small bearing surface on the sclera would be very uncomfortable and would permit the lens to move, particularly in the up and down directions, creating displacement of the lens' curvature at the center. In order to avoid adverse movement of the lens in view of the small scleral bearing area, the teaching in Trombley is obviously only applicable to a pliable lens in which the sagittal depth is not critical.
The present invention is directed to solving the problems set forth above. It is therefore desirable to have a contact lens that conforms with the limbus and a small portion of the sclera to provide a distributed outer bearing area for the lens, and extends under a portion of the eyelid so that the lens is not easily dislodged, such as is often the case with corneal contact lenses. It is also desirable to have a contact lens that is relatively thin, comfortable to wear, and easy to insert and remove. Furthermore it is desirable to have a contact lens that can be worn after corneal surgery, such as keratotomy, in cases where the surgical procedure was not completely successful in achieving the desired visual acuity. Still further, it is desirable to have a contact lens that can mold the cornea to a desired shape by controllably distributing the bearing pressure of the eyelid on both the corneal and scleral portions of the eye.