It is well known to those skilled in the art that intraocular lenses are predominantly designed to replace a previously or simultaneously removed lens in a cataract patient (see, for example, U.S. Pat. No. 5,628,798). However, although the implantation of intraocular lenses has constituted an appreciable surgical advance, such implantation has been known to cause immediate or latent damage to the corneal endothelium, immediate or latent inflammatory responses in the anterior and/or posterior segments of the eye, immediate or latent secondary fibrosis and/or neovascularization, and other problems.
Intraocular lenses have been surgically implanted into an aphakic eye in order to take the place of the natural lens. (See, U.S. Pat. No. 2,834,023). Intraocular lenses have been implanted into the posterior chamber of the phakic eye, i.e., an eye having a natural lens in situ, to compensate for refractive errors or to create a specific refraction to assist in visual function. (See, U.S. Pat. No. 4,769,035).
Certain difficulties are associated with implanting an intraocular lens in the phakic eye that are not encountered when implanting a lens in the aphakic eye. The phakic eye is a substantially more reactive environment than the aphakic eye. Inflammatory reactions tend to be greater in the phakic eye resulting in a concomitant increase in damage to the eye caused by implanting intraocular lenses. One reason is that in the aphakic eye, the natural lens does not pull on the highly reactive ciliary body thus, the ciliary body is in a "resting state" and tends to undergo some degree of atrophy. Additionally, the presence of the natural lens in the phakic eye crowds the area in which an intraocular implant can be placed in the eye.
Placements of intraocular lenses in the posterior chamber of the phakic eye also have been known to cause cataract formation in the natural lens that remains in situ due to contact between the implant and the natural lens. In contrast, implanting intraocular lenses in patients having cataract removal cannot induce such an effect since the natural lens has been removed.
The anterior chamber of an eye is that area in front of the iris and behind the cornea. The iris acts as a divider between the anterior chamber and the posterior chamber. The anterior chamber was originally studied as a preferred location for aphakic intraocular implants particularly when no posterior capsule was present. However, significant drawbacks were discovered.
The phakic eye has a shallower anterior chamber (i.e., the average antero-posterior depth is less) than the aphakic eye, and the iris is in contact with the anatomic lens. Therefore, if an inflammatory reaction occurs in the phakic eye, there can be adherence of the iris to the anterior surface of the anatomic lens. Furthermore, if posterior chamber implants were to cause an inflammatory reaction in the phakic eye, cataract formation may occur in the natural lens which remains in situ.
For intraocular lenses implantation, it was known in the art that the preferred location of the implant was in the posterior chamber, i.e., that area behind the iris and in front of the natural lens in situ. Intraocular implants for the posterior chamber have been designed to treat myopia (nearsightedness) and hyperopia (farsightedness).
However, a drawback existed for correcting refractive errors in patients with high myopia, extreme nearsightedness, with posterior chamber ocular lenses. Because of the high degree of corrective refraction of the optic, which causes the optical zone to be quite small, a myopic posterior chamber lens may irritate the iris and potentially touch the natural lens. Anterior chamber intraocular lenses for high myopia were explored for implantation in the phakic eye which would not be in contact with uveal tissue or the human lens. Hyperopic posterior lenses would not cause similar damage because the edge of a hyperopic lens is thinner and does not project the peripheral iris forward. In addition, the vault of a hyperopic posterior lens prevents human lens touch. Therefore, there is no incentive to place a hyperopic lens into the anterior chamber.
U.S. Pat. No. 4,676,792 discloses an uncoated minus power anterior chamber implant for the treatment of myopia. Uncoated minus power implants have been used in patients having high myopia that is not satisfactorily corrected with spectacles or contact lenses (see, for example, Colin et al., 1990, Refractive and Corneal Surgery 6:245-251 and Baikoffet al., 1990, Refractive and Corneal Surgery 6:252-260). The prior art does not disclose implanting a positive power implant into the anterior chamber of a phakic eye for the treatment of hyperopia. Moreover, due to the shallowness of the anterior chamber in hyperopic eyes, surgical location of a positive power implant in the anterior chamber of the phakic eye for the treatment of hyperopia would be in contravention of, and counterintuitive to, the state of the art.
It has been generally acknowledged by those skilled in the art that there are significant risks involved with the use of anterior chamber angle supported implants in the aphakic eye (reviewed in Apple et al., in Intraocular Lenses: Evolution, Designs, Complications and Pathology (William and Wilkens, Baltimore) 1989, Chapter 4, pp. 59-105) and more so in the phakic eye (Id. at p. 65, col. 1). For example, when such an implant is inserted into the eye, temporary or permanent adhesions of the implant to iris tissue may result, causing damage to these structures to ensue either immediately or over the long term affecting pupillary mobility and contour. In addition, once the implant is in position, it may cause similar angle adhesions due to mechanical and/or chemical inflammation which may lead to fibrosis of a progressive nature. This would make subsequent removal of the implant a complex, dangerous surgical procedure. Other problems associated with such implants are cataract formation, secondary glaucoma, corneal edema, hyphema, and progressive endothelial cell loss, in addition to other complications.
As observed in Ophthalmology Alert, Vol. 1, No. 11 (Nov. 1990), pp. 41-42, Comment on page 42, several American manufacturing companies that were preparing to begin clinical trials of phakic anterior chamber ocular implants in the United States are now likely to abandon these studies, due to the attendant risks associated with anterior chamber implants in the phakic eye and the difficulty of obtaining approval of the U.S. Food and Drug Administration (FDA) for the use of the implants. A significant risk involved in the use of such anterior chamber implants in the phakic eye is the potential for the implanted lens to contact the corneal endothelium, the anatomic lens or the iris with resultant complications, even with the enhanced vault design theorized in the studies discussed in Ophthalmology Alert because such design would bring the lens optic edge quite close to the midperipheral corneal endothelium. One alternative to avoid contact with the corneal endothelium is to reduce the diameter of the optic of the minus power lens, however, such a modification creates significant drawbacks, including glare and haloing under low light conditions, ovalization of the pupil, and, as reported in Perez-Santonja et al., J. Cataract Refract Surg 22:183-187 (1996) (discussing Baikoff ZB5M), induces an inflammatory response.
It would clearly be advantageous to employ an uncoated positive power anterior chamber ocular implant that would avoid the occurrence of the above-described problems associated with anterior chamber implants for the treatment of hyperopia.
Hyperopia, a condition commonly known as farsightedness, has been known to be treated by wearing positive power eyeglasses, contact lenses, and/or surgically implanted iris supported or posterior chamber intraocular lenses. Plastic rings have also been surgically sutured to the sclera for the treatment of hyperopia and presbyopia. It was generally believed by persons of skill in the art that the anterior chamber of the phakic eye of those individuals suffering from hyperopia was more shallow than in the phakic eye of those individuals suffering from myopia. Therefore, attempts to correct hyperopia did not involve implantation of a positive power implant into the anterior chamber of the phakic eye.
U.S. Pat. No. 4,769,035 discloses a posterior chamber implant for implantation in the phakic eye for correction of hyperopia. This posterior chamber implant is designed specifically to come into immediate and direct contact with the anterior surface of the natural lens. The surgical procedure for implanting this posterior chamber implant requires a pre-implantation determination of the precise shape and contouring of the surface of the natural lens and the specific amount of optical correction required for placement of such a lens in direct contact with the natural lens.
U.S. Pat. No. 5,489,299 discloses a method of treating hyperopia and presbyopia wherein the effective working distance of the ciliary muscle can be increased by expanding the sclera in the region of the ciliary body by suturing to the sclera a relatively rigid band having a diameter slightly greater than that of the sclera in the region of the ciliary body. Rings are surgically implanted, and intraocular lenses are not used at all in this procedure.
U.S. Pat. No. 5,192,319 discloses an intraocular lens surgically positioned in the anterior chamber to be used in addition to the natural lens to correct refraction by fixation of such lens on the iris using one or more pairs of pincer-like extensions for holding the position of the lens to the iris tissue. This patent discloses a positive power implant for placement in the anterior chamber of the phakic eye for correction of hyperopia, specifically designed to attach to the iris. Although such positioning on the iris may provide for safe clearance away from vital structures such as the natural lens and the corneal endothelium, the implant has a number of significant drawbacks. Damage may occur to the sensitive iris tissue and the damage is increased when adjusting the position of the implant in cooperation with the existing lens. Also, deterioration of the iris tissue occurs, thereby decreasing the ability to place future replacement implants on the iris. Contact with vital intraocular structures may occur. The patent states at column 4, lines 25-27, that "[a]ll designs are a compromise between the anatomical limitations caused by the position of the intraocular lens in the anterior chamber and the optical requirements." In addition the disadvantages of iris mounted anterior chamber implants are discussed by Apple et al., in Intraocular Lenses: Evolution, Designs, Complications and Pathology (William and Wilkens, Baltimore) 1989 Chapter 3, pp. 45-58, which states on page 58 that such lenses have become obsolete due to numerous complications.
U.S. Pat. No. 4,871,363 also discloses a corrective intraocular lens positioned in the anterior chamber in a phakic eye for correcting high myopia wherein a leading haptic is shorter than the trailing haptic. Such a lens would necessarily be a minus power lens, even though the illustration of FIG. 3 is drawn showing what appears to be a positive power lens, because it is designed specifically for treatment of myopia. The specification of '363 does not provide any disclosure of a positive power ocular lens in a phakic eye for treatment of hyperopia since the invention is limited to the treatment of myopia. Moreover, the intraocular lens that is disclosed in the '363 patent is admitted to be designed primarily for the replacement of a natural lens in an aphakic eye at col. 3, lines 36-44. The '363 patent does not appreciate the problems associated with positive power ocular implants actually implanted into the phakic eye.
U.S. Pat. No. 4,676,792 discloses a minus power intraocular implant for placement in the anterior chamber of the phakic eye for the treatment of myopia. Although FIG. 2 of the '792 patent shows a convex anterior surface of the optic, the optic is minus power due to the concave curvature of the posterior surface of the optic. The '792 patent does not appreciate the complications associated with a planar or convex posterior surface of the optic in combination with a convex or planar anterior surface.
To Applicant's knowledge, there has not been a successful implantation of a positive power anterior chamber ocular implant angle supported in the phakic eye for the treatment of hyperopia. In view of the problems and risks encountered with the development of minus power anterior chamber intraocular lenses, it would have been unexpected for positive power anterior chamber intraocular lenses to be successfully modified for use in the phakic eye for the treatment of hyperopia.
It is an object of the present invention to provide a positive power ocular implant for placement in the anterior chamber of a phakic eye to correct refractive errors caused by hyperopia.