Method of Treating Intraocular Lens and the Like

H. E. Kaufman, M.D. and others have identified a serious problem in intraocular lens implantation dealing with the destruction of corneal endothelium cells. It is generally recognized that the corneal endothelium will not regenerate itself and is extremely important as a boundary layer between the outer layers of the cornea and the aqueous humor in the anterior chamber of the eye. The corneal endothelium is extremely delicate in that the endothelium is only one cell thick.

The intraocular lenses commonly implanted are of a polymethylmethacrylate (PMMA) material which has excellent optical qualities and biocompatibility once it is surgically implanted. Once implanted the location of the intraocular lens is such that, when in its proper position, it does not contact or damage the corneal endothelium. There is a continuous washing or flushing of the anterior chamber including the corneal endothelium.

During surgical implantation of an intraocular lens, the cornea is surgically opened and the intraocular lens manipulated in place frequently with retention loops placed behind the iris. Sometimes the manipulation includes puncturing the iris with a miniature safety pin type prong or clip to attach the lens to the iris.

During the surgical implantation and manipulation, it frequently happens that the corneal endothelium is staticly touched or dynamically scraped with a PMMA lens or surgical tool. Dr. Kaufman and others have recognized the problem of corneal endothelium damage during surgery and have proposed dipping the lens in a coating of methylcellulose (MC) or polyvinylpyrrolidone (PVP). These coatings were applied by the ophthalmologist immediately prior to surgery as a wet and slippery coating on the lenses.

Dipping of the lenses in MC or PVP is useful to protect the corneal endothelium. However, because of a fast dissolution rate of these polymers and the difficulty of placing a controlled amount of such polymers on the lenses, the extent and length of the protection is uncontrollable. Because of the wet and slippery nature of the lenses dipped during surgery, the lenses are difficult to handle and a portion of the coating may drip off. In addition, MC and PVP solutions must be sterilized prior to dipping. Subsequently, Dr. Fechner (citation below) published the results of a repeat of the Dr. Kaufman et al experiments with a complicated attempt to sterilize methylcellulose in very small quantities to keep it from coalescing and changing viscosity. In practice, the complicated procedure described for the sterile methylcellulose coating is not feasible for the ophthalmologist to perform in the operating room.

The background publications by Dr. Kaufman et al explaining the corneal endothelium damage during intraocular lens implantation and experiments with methylcellulose and polyvinylpyrrolidone coating are as follows.

Kaufman, H. E. and J. I. Katz, "Endothelial Damage From Intraocular Lens Insertion," Inv. Ophth., Vol. 15(12), Dec. 1976, p. 996-1000

Kaufman, H. E., Jeffry Katz, et al, "Prevention of Endothelial Damage From Intraocular Lens Insertion," Tr. Am. Acad. Ophth. & Otol., Vol. 83, Mar-Apr. 1977, p. 204-212

Kaufman, H. E. and J. I. Katz, "Pathology of the Corneal Endothelium," Inv. Ophth. Visual Sci., Vol. 16(4), April 1977, p. 265-268

Fechner, P. U., "Methylcellulose In Lens Implantation," Jour. Amer. Intraocular Implant Society, Vol. 3(3 & 4), July-October 1977, p. 180-181

Kaufman, H. E., Jeffrey Katz, et al, "Corneal Endothelium Damage with Intraocular Lenses: Contact Adhesion Between Surgical Materials and Tissue," Science, Vol. 198(4316), Nov. 4, 1977, p. 525-527.

The present invention includes a method of precoating an intraocular lens or surgical tool with a liquid media containing a water-soluble adherent film forming material, such as polyvinyl alcohol, and then removing the liquid media by evaporation. The lens or tool with its firmly adherent dry coating is then packaged and sterilized, such as by ethylene oxide.

Immediately prior to its use in surgery, the ophthalmologist rehydrates the lens or tool simply by dipping it into a sterile liquid of normal saline or a balanced salt solution. This swells the coating into a spongey sluffable protective layer that protects the corneal endothelium during static touch contact as well as dynamic sliding contact with the coated lens or surgical tool. After implantation, the continual flushing action of the anterior chamber of the eye removes the coating from the lens in a period of several hours.

The present application deals with the method of treating the intraocular lens or surgical tool. A related application by the same inventors is entitled "Intraocular Lens And Surgical Tool For Implanting Same," filed Nov. 30, 1977, Ser. No. 855,961, relates to the coated lens and surgical tools themselves.

FIG. 1 is a rear prospective view of an intraocular lens which has been coated according to such process;

FIG. 2 is a schematic view showing the dip coating step of the process;

FIG. 3 is an enlarged sectional view of the lens after its coating has been dehydrated;

FIG. 4 is a schematic view showing the lens submerged in a liquid during the rehydrating step;

FIG. 5 is an enlarged sectional view showing the swollen coating in rehydrated state; and

FIG. 6 is a prospective view of an ophthalmic surgery forceps with the rehydrated coating on such tip sections.

FIG. 1 shows a typical intraocular lens with an optical section shown generally at 1 with a pair of looped sections 2 and 3 that are joined to the optical section by shank portions, such as at 4. The optical section 1 has a coating 5 that covers its entire front surface, its outer edge, and a circumferential band 6 at its rear portion. If desired, circumferential band 6 could be eliminated with the coating covering only the optical section's front and peripheral edge.

It is preferable that loop sections 2 and 3 not be coated, because such coating tends to bridge the loop sections and introduce more coating material into the eye than is actually needed. The front and peripheral edges of the optical section 1 are those areas of the intraocular lens most likely to contact the corneal endothelium.

The method of making the intraocular lens of this invention includes forming the lens, and then dipping only that portion intended to be coated in a water solution of the water-soluble material. Excellent results have been obtained by dip coating the lens in a 5% aqueous solution of polyvinyl alcohol. Although 5% concentration of polyvinyl alcohol (PVA) is used, the concentration could be varied from 1% to 60% depending upon the thickness of coating desired and the number of dips. Preferably two dip coats are applied with an air drying step between the coats.

Once the complete coating has been applied, the water or other liquid media is removed by evaporative drying. A substantially dry very adherent film remains on the lens. It is important that the coating material be a good film former and not "bead up" to expose certain uncoated areas of the lens. Polyvinyl alcohol is an excellent film former.

The lens as shown in FIG. 3 with its substantially dry coating is then packaged and subjected to sterilization, such as by ethylene oxide. Because there are many different package designs that could be used, it is not believed necessary to schematically show a package nor to illustrate the equipment for sterilizing such packaged lens.

The lens in its packaged sterilized form with its dehydrated coating is supplied to the ophthalmologist. Immediately prior to insertion of the lens, the ophthalmologist rehydrates the lens by submerging it in a sterile liquid, such as normal saline or a balanced salt solution. After this rehydration step, which takes approximately 1 to 10 minutes at room temperature, the coated lens has a swollen cushion as shown in FIG. 5. Good results have been obtained with rehydration for 5 minutes. It is estimated that the hydrated coating has a thickness of approximately 10 to 1000 microns, while the dehydrated coating has a thickness of approximately 5 to 300 microns.

Once the intraocular lens has been surgically implanted, the continuous biological flushing action of the aqueous humor in the anterior chamber dissolves the coating from the lens. The coating is believed to eventually be excreted through the urine.

FIG. 6 shows a rehydrated coating 7 and 8 on tip sections 9 and 10 of an ophthalmic surgery tool that is likely to contact the corneal endothelium. An example of such tool is a Hirshman spatula.

Once the intraocular lens or surgical tool has been rehydrated as explained above, it is important that a rehydrated film does not quickly dehydrate when exposed to air. It has been found that the polyvinyl alcohol in rehydrated form will maintain its rehydrated state in a time range of 20 minutes 11/2 hours. In a typical intraocular lens implant, the cornea is surgically opened for about 1/2 hour. Also during the surgery, the coated lens or tool is flushed with liquid and also in contact with the aqueous humor of the anterior chamber which tends to delay a dehydration of the coating by air drying.

The polyvinyl alcohol coating is much superior to the previously proposed methylcellulose or polyvinylpyrrolidone coatings. A sample of methylcellulose used by Dr. Kaufman as the basis for his publications was obtained from him. Tests showed that this material "beaded up" and exposed edges of the lens. It also dissolved too quickly. A polyvinylpyrrolidone coated lens was submerged in approximately 0.2 ml of water simulating a surgical site. Approximately 25% of PVP remained after 30 minutes.

The polyvinyl alcohol performs exceptionally well as a coating for intraocular lenses or the like. It is hydrophilic, soluble in water, swellable upon rehydration, an excellent film former, performs well on both static touch and dynamic sliding tests on the corneal endothelium has slower dissolution rate than other materials previously reported. It also does not dehydrate in the operating room for a period of 20 minutes after it has been rehydrated, and is easily cleared from the anterior chamber of the eye through biological processes. When the PVA is submerged in a simulated anterior chamber, i.e. 0.2 ml of water, approximately 75% of the PVA remains on the lens.

Other water-soluble polymers besides polyvinyl alcohol meeting the above criteria could also be used. Examples of such other materials are hydroxypropyl methylcellulose, and hydroxypropyl cellulose which retain approximately 50% of the coating weight when submerged in a simulated ocular surgical site as explained above. In this invention, it is preferable that the coating retain at least 40% of its weight after such submersion for 30 minutes. Should different materials meeting the above criteria be used, they would still be processed through the dehydrating, sterilization, and rehydrating step to provide very convenient precoated intraocular lenses and surgical tools to the ophthalmologist.

This method could be used with anterior chamber lenses, posterior chamber lenses, and lenses which use retention means other than iris loops.

In the previous description, specific examples have been used to describe the invention. However, it is understood by those skilled in the art that certain modifications can be made to these examples without departing from the spirit and scope of the invention.