WO1985003247A1

WO1985003247A1 - Method for cleaning contact lenses

Info

Publication number: WO1985003247A1
Application number: PCT/US1985/000079
Authority: WO
Inventors: Daniel Perlman
Original assignee: Eye Products Limited Partnership
Priority date: 1984-01-20
Filing date: 1985-01-17
Publication date: 1985-08-01
Also published as: AU3889685A; EP0168487A1

Abstract

A method for cleaning a contact lens wherein the lens is contacted with a solution containing a heat stable proteolytic enzyme at an elevated temperature for a period of time sufficient to clean said lens. Preferably, the method is accomplished during a conventional heat disinfection cycle where the lens is conveniently cleaned and disinfected in one step.

Description

METHOD FOR CLEANING CONTACT LENSES

Field of the Invention

This invention relates to methods for cleaning contact lenses, particularly to methods involving the use of enzyme solutions, and more particularly to methods using enzyme solutions at elevated temperatures and to methods for accomplishing a one-step process for thermal disinfection and cleaning of contact lenses.

Background of the Invention

As contact lenses are worn, matter from the tear film such as proteins, lipids and salts deposit on the lens. Likewise, foreign materials such as oils, handcreams, grease, hairspray, and the like, can contaminate the lens surface. These deposits must be cleaned from the lens periodically to maintain clear vision and to avoid irritation to the eye. This cleaning step generally must be followed by a separate disinfection step, necessitating a two-step process which is both time-consuming and inconvenient. This has limited proper cleaning of lenses to less than optimal frequency for most wearers. Indeed, most wearers disinfect daily but clean with enzymes only about once a week. Thus, a more convenient and less time-consuming method for accomplishing these two steps is highly desirable.

Numerous procedures and solutions have been devised to clean lenses with only partial success. Procedures include mechanical rubbing of the lens, ultrasonic cleaning, hypertonic solutions, surfactant cleaners, enzymatic cleaners, and oxidative cleaners.

Certain enzymes known as proteases or as peptidases have long been known to degrade proteins. This function of proteases or peptidases has been used for cleaning soft contact lenses. Lo, Silverman and Korb, J. Am. Optom. Assoc., 40 (11) (1969) published a finding that commercial protease-containing detergents specifically removed protein from contact lenses. U.S. 3,910,296 describes the removal of proteinaceous material on the surface of contact lenses, especially soft contact lenses, by contacting the lens for a time sufficient to clean the lens with a substantially isotonic, aqueous solution containing an effective amount of a protease such as papain. Non-toxic compounds containing sulfhydryl groups are included to activate the papain.

U.S.4,096,870 describes the removal of proteinaceous material on the surfaces of hydrophilic gel contact lenses (soft lenses) by contacting the lenses with an aqueous suspension of pancreatin without absorption of pancreatin into the lens structure. Pancreatin is an enzyme mixture purified from animal pancreas that contains protease, lipase (lipid or fat-digesting enzyme) and carbohydrase (carbohydrate-digesting enzyme) activities and is active without the addition of compounds containing sulfhydryl groups. The pancreatin is commercially formulated as tablets using sodium chloride and boric acid to provide a measured amount of pancreatin for cleaning contact lenses.

U.S.4,285,738 describes the removal of proteinaceous matter lodged on the surface of a contact lens by immersion of the lens in an aqueous bypertonic composition containing urea or a salt of guanidine and a reducing agent such as a sulfite, a pyrosulfite, etc., and preferably by adding a proteolytic enzyme, even in an amount not effective when the enzyme is used in the absence of urea or a guanidine salt.

European Patent Application Publication No. 0005131 describes hypertonic cleaning solutions for soft contact lenses wherein the solution contains a lipolytic enzyme (or lipase) and, optionally, a proteolytic enzyme (or protease). The resulting degradation products are removed by rinsing. The lenses are then disinfected by boiling in a physiological saline solution. Another description of cleaning solutions for contact lenses containing a combination of enzymes can be found in Japanese Kokai Tokkyo Kbho JP 82/48,712 (Chem. Abs.97:78933d).

Enzyme cleaning of contact lenses typically is achieved by placing the lenses in an enzyme cleaning solution for a period varying from two hours to overnight. Generally the cleaning is then followed by disinfection of the lens in saline solution. The disinfection step is required because enzyme cleaning solutions are typically non-sterile and are potential growth media for microorganisms. Since the lens must be disinfected prior to insertion in the eye, disinfection must always follow this type of enzyme cleaning. Further, protein which is deposited on the lens is believed to be baked on when the heat disinfection process is used, making removal more difficult or impossible. An ideal cleaning and disinfection regime always would remove protein deposits prior to any heat disinfection step.

Some enzyme cleaning solutions have been combined with chemical disinfection to avoid the heat disinfection step. See, for example, Japanese Tokkyo Koho JP 82/24,526 (Chem. Abs. 97:168953g) . However, chemical disinfection frequently leaves residues which cause various ocular problems including ocular irritation and long term allergic responses.

Because of the time required for prior art cleaning of proteinaceous deposits with enzyme (at least two hours and preferably overnight) and the requirement for heat disinfection thereafter (typically forty-five minutes to one hour), in practice lenses are not cleaned as often as is medically desirable. Thus, the deposits of protein and lipids build up and eventually become virtually impossible to remove, requiring replacement of the lenses.

Hence, it is desirable to have a more convenient method for cleaning soft contact lenses so that they will be cleaned more frequently. It is also desirable to have a method for cleaning heavy deposits from lenses that would otherwise be discarded. summary of the Invention

The present invention provides a substantially more convenient and efficacious method for cleaning and disinfecting contact lenses, particularly soft or bydrophilic lenses. In accord with the present invention, enzyme cleaning and thermal disinfection can be accomplished conveniently in one step. Any lens which can tolerate thermal disinfection temperatures can be treated in one step by this technique. This method can also clean contact lenses which were uncleanable by prior art methods. The method of the invention comprises contacting a contact lens with a solution containing a heat stable proteolytic enzyme at an elevated temperature, that is sufficiently high to soften lipid deposits on said lens, for a predetermined period of time to clean said lens.

In one embodiment, during a normal heat disinfection cycle this invention surprisingly and conveniently cleans contact lenses, particularly soft contact lenses, having light to moderate deposits of protein and lipids during a normal heat disinfection cycle, making it extremely convenient to both clean and disinfect such lenses in one convenient step. Recently, it has been recognized that heat disinfection prior to complete cleaning compromises both the lens and the eye because protein deposits are baked onto the lens by the elevated temperatures. Indeed, protein deposits do build up on lenses and become impossible to clean off by prior art methods, thus necessitating the discarding of such lenses. However, it now has been found that some lenses that would have been discarded as uncleanable by prior art methods are remarkably cleaned by the method of the present invention and can continue to be used.

For purposes of this invention, a "heat stable" (thermostable) enzyme is an enzyme that has a half-life of activity, tig, of fifteen minutes or more at 60°C.

Brief Description of the Drawings FIGS. 1A-1D are photographs taken at 320x of representative fields of sectors of a contact lens cleaned with solutions having various concentrations of enzyme in accord with the present invention.

FIGS. 2A-2D are photographs taken as 320x of representative fields of sectors of another contact lens cleaned with solutions having various concentrations of enzyme in accord with the present invention.

FIGS. 3A-3F are photographs of sectors of a contact lens which were cleaned by various methods for comparison and then stained with dye to visualize the amount of protein remaining on the lens sector.

FIGS.4A-4F are photographs of sectos of another contact lens which were cleaned by variousmethods for comparison and then stained with dye to visualize the amount of protein remaining on the lens sector.

Detailed Description of the Invention

In accord with one embodiment of the present invention, proteinaceous and lipid materials on the surface of soft hydrophilic contact lenses are removed and the lenses disinfected by heating the lenses in a solution containing a heat stable proteolytic enzyme for a period of time sufficient to achieve both cleaning and disinfection. Preferably, the proteolytic enzyme is employed in solution at a temperature sufficiently high and for a suitable period of time to:

1. soften lipid and/or other deposits on said lenses;

2. increase substantially the enzyme reaction rate; and

3. provide proper thermal disinfection. Further, the cleaning solution is preferably isotonic or substantially isotonic. Thus, the lens can be rinsed briefly with saline and ready to wear. While it is desirable that the heating process meet the minimum requirements for heat disinfection, thereby achieving both cleaning and disinfecting in a one-step process, this technique can be utilized in temperatures lower than those required for disinfection providing that a temperature of at least 60°C is used. This may be necessary for certain types of lenses which cannot tolerate conventional disinfection temperatures.

Any proteolytic enzyme that is heat stable or that can be stabilized in solution so that it has a t½ of fifteen minutes or more at a temperature of 60°C is useful for the practice of the present invention. Enzymes suitable for the practice of this invention are thermolysin, papain and chymopapain (available from Calbiochem Behring or Sigma Chemical Co.,) caldolysin, (see European Patent Application Publication No.0024182), aminopeptidase I, endopeptidase of Bacillus stearothermophilus thermitase, thermcmycolin, and the like. Suprisingly, papain in its pure crystalline form or in its crude form has been found highly useful in the practice of the present invention. I have found that papain retains its activity in solution for a sufficient length of time at temperatures below about 82°C to obtain remarkable and rapid cleaning in accord with the invention.

A temperature of at least 60°C should be used for cleaning contact lenses in accord with the method of the present invention. Preferably, the temperature should be at least 70°C and, more preferably, 80°C or higher. The only limitations on temperature are those imposed by the nature of the contact lenses and by the thermostability of the enzyme utilized. The temperature should not be too high so that the lens is deformed or otherwise degraded, or so that the enzyme is denatured before cleaning can be accomplished. It is highly preferred that the temperature cycle used for cleaning be the same as that required for heat disinfection, i.e. at least 80°C for a minimum of 10 minutes.

The time required for cleaning will vary depending upon the concentration of enzyme in the cleaning solution, the composition of the cleaning solution, the temperature used for cleaning, the amount of protein and lipid deposits on the lens, etc. It has been found that very good cleaning for normally dirty lenses can be obtained using the enzymes thermolysin, papain and chymopapain with the temperature cycle and time period for conventional heat disinfection processes (reaching at least 80°C for minimum 10 minutes). Heating for 15 minutes at 80°C using 1.0mg/ml crude papain (Prolase 300) has been found to clean most lenses. More than one cleaning cycle may be used to clean lenses having unusually heavy deposits.

The cleaning solution can contain, in addition to the proteolytic enzyme, other agents to stabilize the enzyme, to enhance and/or facilitate the activity of the enzyme, facilitate the removal of enzyme degradation products, etc., or agents to enhance cleaning by other mechanisms. Examples of such agents include, for instance, buffering agents, surfactants, solvents, hypertonic solution additives, sulfhydryl containing compounds, oxidizing agents, reducing agents, lipases, carbohydrases, and the like, etc. For example, an amount of calcium ion in the range of 1 to 10mM is important for the thermostability of thermolysin and caldolysin. Cysteine has been found to enhance the cleaning activity of many proteases. Polyethylene glycol (PEG, MW: 4000-6000) has been found to be beneficial as a wetting agent in amounts as low as 0.02% (w/v).

A simple borate-buffered isotonic saline solution containing a low concentration (5mM) of calcium ion has proved effective for enzymatic cleaning using thermolysin. A typical composition for this buffer (which is hereinafter called CBS buffer) is 0.9% Nad, 10mM boric acid, 0.4mM sodium borate, and 5mM CaCl₂, which is hereinafter called CBS buffer.

When using papain, in either its crude form or its pure crystalline form, a conventional buffer system comprising 0.02% KH₂PO₄, 0.2% NaHCO₃; 0.08% Na₂EDTA, 0.73% NaCl, 0.02% PEG 4000 and 0.1% cysteine hydrochloride (hereinafter PBS solution) has been found to provide highly effective cleaning. However, it has been found that the pH of this buffer system may increase to a value above 9 during heating and/or subsequent storage due to the evolution of CO₂. Such a pH may cause eye irritation if the solution is not thoroughly washed from the lens.

Thus, a thermostable buffer system is preferred for the practice of the present invention. By thermostable buffer is meant a buffer which maintains a nearly constant pH when heated in the cleaning and disinfection cycle in accord with the present invention. A buffer which contains a heat unstable component (such as NaHCO₃, which decomposes liberating CO₂) is not thermostable. A suitable thermostable buffer system for use with papain comprises 10mM boric acid, 5mM to 10mM sodium borate, 2mM disodium EDTA (ethylenediaminetetra acetic acid), 125mM sodium chloride, 0.02% PEG 4000, and 0.1% cysteine.

The particular buffer system preferably is chosen to control the pH of the solution for optimal cleaning and to provide a pH which is compatible with that of the patient's eye. This buffering function can be controlled in many ways. The buffer system may be a thermostable system or the amount of volatile or unstable components can be carefully controlled to keep variations of pH within acceptable limits. Thus, the buffer system used for cleaning solutions in accord with the present invention at least should provide control of pH in a range wherein: (1) the enzyme has good activity; (2) the components of the cleaning solution remain in solution; and (3) eye irritation is minimized even though the lens is not rinsed thoroughly.

Enzymes preferred for the practice of this invention are natural proteases such as those listed above which have good activity within a broad range of pH. With regard to component solubility, cysteine oxidizes to form cystine, which is quite insoluble between pH 2 and 8. Thus, it is desirable to have a pH greater than 8, and preferably in the range of 8.2 to 8.6, when using cysteine in the cleaning solution in accord with the present invention. The pH of tears is variable with the norm considered to be 7.4 to 7.5. However, it can be as low as 5.2 or as high as 8.35. A typical pH range of comfort for the average eye is considered to fall between 6.6 and 7.8. The approximate limits of pH outside of which tissue epithelial damage occurs are 4.0 and 10.0.

Using a pH up to 8.6 in the cleaning solution in accord with this invention does not cause discomfort to the typical patient.

Ohe ingredients for preparing a cleaning solution in accord with the present invention are conveniently packaged as a powder or in tablet form as a unit dose sufficient to prepare from about 1 to 10 ml of cleaning solution for one cleaning. One composition suitable for making one milliliter of thermolysin-based cleaning solution comprises 1.5mg thermolysin, 0.87mg boric acid, 1.2mg sodium borate .1H₂O, 0.75mg calcium chloride .2H₂O, 1.0mg cysteine hydrochloride, 7.3mg sodium chloride, and distilled H₂O to make 1ml. Preferably, 0.4mg of PEG 4000 also is added. The ingredients can be formulated in a tablet with or without the enzyme, the enzyme being supplied separately in a packet, if desired. Alternatively, the entire composition can be packaged as a powder to facilitate dissolution. Formulations may differ depending upon whether the intended use is for regular maintenance or heavy duty cleaning.

In another embodiment of the invention, a papain-based cleaning solution can be formulated from the following ingredients: 0.5mg cystalline papain or 5.0mg crude papain (commercially available as Prolase 300) , 3.1mg boric acid, 10.9mg sodium borate.1H₂O, 3.7mg disodium EDTA, 36.5mg sodium chloride, 1.0mg PEG 4000, 5.0mg cysteine, and distilled H₂O to make 5ml. As with the thermolysin formulation above, this papain formulation can be provided as a powder or in tablet form. The enzyme can be included in the tablet or powder, or packaged separately.

All percentages above are weight/volume percents. I have found that layers of lipid materials are formed on top of and/or between protein layers on soft contact lenses. Although not wishing to be bound by theory, I have found that at room temperature these lipid deposits are waxy, semi-solid and water-repellant, thus protecting the protein layer from proteolytic degradation. At elevated temperatures, approximately 60°C and above, these lipid materials soften and become mobile and oily. The lipid materials then move about and the protein layer becomes accessible to enzyme degradation, thereby enabling the remarkable cleaning obtained by the method of the present invention.

Many lenses which have proven refractory to cleaning by conventional methods (using commercial Allergan papain preparation or Alcon pancreatin preparation as recommended by the manufacturers), and which lenses had been retired from use were,in fact, remarkably cleaned by the method of the present invention. This was achieved with, for example, thermolysin, papain and chyraopapainrbased cleaning solutions. The heating and disinfection which accompanies heat stable enzyme cleaning in accord with the present invention has additional benefit. Conventional enzyme solutions in physiological buffers are non-sterile. Because these solutions can support growth of microorganisms, the lens must be disinfected after enzyme cleaning prior to wearing. Debris from the growth of these microorganisms during the conventional cleaning step may renain and be baked onto the lens in the course of disinfection. Heat disinfection of the enzyme solution during cleaning in accord with the present invention prevents this problan.

The invention will be further illustrated by the Examples which follow.

Example 1.

A Hydromarc hydrophilic soft contact lens which was heavily and uniformly coated during human use was treated first with Allergan commercial papain preparation and second with Alcon commercial pancreatin preparation according to the furnished directions. No cleaning was detectable by microscopic analysis. The lens was then divided by razor blade into four equal sectors, one piece being placed in each of four solutions of CBS buffer containing 0, 0.1, 0.4 or 1.6mg/ml thermolysin. The lens sectors were incubated at 80°C for 2 hours. The lens sectors were rinsed with saline, stained with Coomassie Brilliant Blue Stain for one minute, rinsed with an aqueous methanol solution and photographed at 320x magnification using 35 mm Kodak Plus-X-pan film. A photograph of a representative field from each piece is illustrated in FIG. 1A through 1D, respectively. It is readily seen that dramatic cleaning occurred with 0.4mg/ml thermolysin and almost complete cleaning occurred with 1.6mg/ml.

Example 2.

A Syntex CSI hydrophilic soft contact lens was heavily and uniformly coated during human use. As in Example 1, the lens was not cleaned by either Allergan's papain preparation or Alcon's pancreatin preparation. Subsequently, the lens was divided into sectors and the sectors incubated as in Example 1 with 0.0, 0.2, 0.4, or 1.6mg/ml thermolysin. The lens sectors were analyzed as in Example 1. Photographs of representative fields of the sectors cleaned with enzyme concentrations of 0, 0.2, 0.4 and 1.6mg/ml are shown in FIG. 2A through 2D, respectively. Again, increasing enzyme concentrations yielded increasingly clean lens sectors. A concentration of 1.6mg/ml thermolysin produced essentially clean lens surfaces.

Example 3.

Two Syntex CSI lenses lightly coated with intermittent film and debris visible by light microscopy were cut into sectors and enzymatically treated and examined as in Example 1. In both lenses, thermolysin concentrations of 0.2 - 0.4mg/ml produced essentially clean lenses.

Example 4.

Eight hydrophilic soft contact lenses coated with protein and lipid materials after human use and refractory to conventional enzyme cleaning by the patients were soaked in normal saline and each was cut into six equal sectors. These sectors designated A through F were incubated for 3 hours as follows:

(A) with Allergan commercial papain preparation as per user directions;

(B) with 0.5mg/ml recrystallized papain (Sigma P4762) in buffer containing 20mM tris-HCl pH 8.0, 5mM cysteine and 2mM EDTA;

(C) with Alcon pancreatin as per user directions;

(D) with 1mg/ml commercial pancreatin (Sigma, P1750) suspended in 0.9% saline;

(E) with 0.5mg/ml thermolysin (Calbiochem-Behring) dissolved in CBS buffer; and

(F) with 0.9% saline (control).

The incubation temperature was 23°C for all samples except the (E) samples, which were incubated at 80°C in accord with the teachings of the present invention. Following incubation the lens sectors were rinsed with saline, stained as in Example 1, examined by light microscopy and photographed using a conventional camera fitted with a macrolens. Photographs of the stained sectors for two of the lenses are shown in Figures 3(A-F) and 4(A-F) , for illustration. Both macroscopic and microscopic examination revealed negligible cleaning of any lens sectors treated under protocols A, B, C and D (i.e. they showed comparable contamination to that of the untreated sector F, the control sample). In contrast, thermolysin (treatment E) produced dramatic and effective cleaning of most lens sectors. The thermolysin-treated lens sectors are designated by the letter E in Figures 3 and 4. Example 5.

Several hydrophilic soft contact lenses were cleaned with 1.5mg/ml thermolysin in CBS buffer at 80°C for 3 hours to determine whether enzyme treatment at elevated temperature had any effect on the optical prescription of the lenses. The lenses and prescriptions were as follows:

Lens Type Optical Strength Diameter

1. Hydrocurve II +13.00 15.1

2. CSI - 6.50 15.0

3. Hydromarc - 5.00 14.9

4. CSI + 7.75 13.8

5. CSI + 7.50 13.9

6. Hydromarc - 3.75 14.5

No detectable change in these prescriptions occurred with enzyme treatment.

Example 6.

A Bausch & Lomb Softlens and a CSI lens were boiled for 30 minutes in a solution containing 0.1% Lysozyme (w/v) in a modified CBS buffer. The modified CBS buffer solution was formulated as follows: 14mM H₃BO₃; 5.5mM Na₂B₄O₇.10H₂O; 5mM CaCl₂.2H₂O; 5.7mM Cysteine.HCl; and 125mM NaCl.

The lenses were incubated at 84°C for 30 minutes in modified CBS buffer solution containing 0.5mg/ml of thermolysin. The denatured protein deposited from the Lysozyme solution was completely removed from both lenses.

Example 7.

Three hydrophilic lenses which had been subjected to human use were cut into sectors and were treated by incubation for two hours at 80°C in 1ml of cleaning solution as follows: (A) a CBS buffer solution with 1mg/ml cysteine hydrochloride (control);

(B) a thermolysin solution (0.5mg/ml) buffered with CBS containing 1mg/ml cysteine hydrochloride; and

(C) a Prolase 300 solution (1mg/ml) buffered with PBS. After treatment of lens 1, a Hydromarc lens, inspection of the three sectors under a microscope revealed:

I. Control-Treatment (A) : a course granular continuous coating;

II. Thermolysin-Treatment (B): almost clean, thin patches of deposits remaining, tiny droplets of oily substance on surface; and

III. Prolase 300-Treatment (C) : same results as for treatment (B) as described above.

Lens 2, another Hydromarc lens, and lens 3, a CSI lens, showed similar results to those for lens 1.

Example 8.

The experiment of Example 7 was repeated using additional sectors from each of the same three lenses. The cleaning solutions were the same as in Example 7 with the exception that 0.25mg/ml of crystalline papain was substituted for the Prolase 300 of treatment (C) . Results were virtually identical to those of Example 7.

Example 9.

A Bausch & Lomb lens having a heavy coating and a CSI lens having a very heavy coating, both from actual human use, were cut into sectors and treated as in Example 7 except that in treatment (C) crystalline papain at 0.5mg/ml was substituted for the Prolase 300.

The Bausch & Lomb lens sectors were not able to be cleaned using either treatment. The sectors of the CSI lens after incubation at 80°C for 2.5 hours appeared as follows: I. Control-Treatment (A): rough continuous, non-granular coating (very heavy) over entire lens;

II. Thermolysin-Treatment (B) : about 30% of the lens surface was still coated; and

III. Crystalline Papain-Treatment (C) : lens almost clean, with only thin trace patches of protein remaining.

Example 10.

A new Ciba and a new hydromarc lens were coated with

Lysozyme as described in Example 6. Both lenses were then cleaned with the Prolase 300 solution of Treatment (C) of Example 7 at a temperature of 80°C. Rates of cleaning were monitored for each lens by observing change in optical density at 280 nm. The lenses were completely cleaned with this procedure. Thai the lenses were recoated as above and the experiment was repeated substituting crystalline papain at a concentration of 0.1mg/ml for the Prolase 300. Rates of protein removal were approximately 3 times more rapid with the crystalline papain treatment. This invention has been described in detail with reference to the preferred embodiments thereof. However, it will be appreciated that modifications and improvements may be made by those skilled in the art upon consideration of the specification.

Claims

I Claim:

1. A method for cleaning a contact lens, said method coπprising contacting said lens with a solution containing a heat stable proteolytic enzyme at an elevated temperature for a period of time sufficient to clean said lens.

2. The method of claim 1 wherein said heat stable enzyme is thermolysin, caldolysin, aminopeptidase I, endopeptidase of Bacillus stearothermophilus thermitase, thermomycolin, papain or chymopapain.

3. The method of claim 1 wherein said enzyme is thermolysin or caldolysin.

4. The method of claim 1 wherein said enzyme is papain or chymopapain.

5. The method of claim 1 wherein said solution contains cysteine.

6. The method of claim 1 wherein said temperature is 80°C or more.

7. The method of claim 1 wherein said teπperature and time period are achieved in a conventional heat disinfection cycle.

8. The method of claim 1 wherein said solution comprises thermolysin or caldolysin as the heat stable enzyme, calcium chloride, and a buffer.

9. The method of claim 8 wherein said buffer comprises boric acid and sodium borate.

10. The method of claim 8 wherein said solution is isotonic.

11. The method of claim 8 wherein said solution further contains cysteine.

12. The method of claim 8 wherein said solution further contains a wetting agent.

13. The method of claim 8 wherein said wetting agent is polyethylene glycol.

14. The method of claim 1 wherein said enzyme is papain.

15. The method of claim 14 wherein the temperature is maintained at about 80°C for about fifteen minutes.

16. The method of claim 14 wherein said solution comprises a heat stable buffer system.

17. The method of claim 16 wherein said buffer system comprises boric acid and sodium borate.

18. The method of claim 17 wherein said solution further contains Na₂EDTA and cysteine.

19. The method of claim 18 wherein said solution contains a wetting agent.

20. The method of claim 19 wherein said wetting agent is polyethylene glycol.

21. The method of claim 14 wherein said papain is pure crystalline papain.

22. The method of claim 14 wherein said papain is crude papain.

23. A method for cleaning a contact lens, said method coπprising contacting said lens with a solution containing a heat stable proteolytic enzyme for a period of time sufficient to clean and disinfect said lens.

24. The method of claim 23 wherein said heat stable enzyme is thermolysin, caldolysin, aminopeptidase I, endopeptidase of Bacillus stearothermophilus thermitase, thermomycolin, papain or chymopapain.

25. The method of claim 23 wherein said enzyme is thermolysin or caldolysin.

26. The method of claim 23 wherein said enzyme is papain or chymopapain.

27. The method of claim 23 wherein said solution comprises thermolysin or caldolysin as the heat stable enzyme, calcium chloride, and a buffer.

28. The method of claim 27 wherein said buffer comprises boric acid and sodium borate.

29. The method of claim 23 wherein said enzyme is papain.

30. The method of claim 29 wherein said solution comprises a heat stable buffer system.

31. The method of claim 30 wherein said buffer system comprises boric acid and sodium borate.

32. A composition useful for cleaning contact lenses, said composition comprising thermolysin, boric acid, sodium borate, calcium chloride and sodium chloride.

33. The composition of claim 32 further including cysteine and polyethylene glycol.

34. The composition of claim 32 wherein thermolysin is replaced with caldolysin.

35. The composition of claim 32 in tablet form.

36. A unit package of a cleaning composition suitable for forming 1 ml of a cleaning solution for contact lenses, said package comprising 1.5mg thermolysin, 0.87mg boric acid, 2.1mg sodium borate .10H₂O, 1.0mg cysteine hydrochloride, 0.75mg calcium chloride .2H₂O, and 7.3mg of sodium chloride.

37. The unit package of claim 36 formulated as a tablet.

38. The package of claim 36 further comprising 0.4mg of polyethylene glycol.

39. The package of claim 38 formulated as a tablet.

40. The package of claim 36 wherein caldolysin is substituted for thermolysin.

41. The unit package of a cleaning composition suitable for forming 5ml of a cleaning solution for contact lenses, said package comprising 0.5mg crystalline papain or 5.0mg Prolase, 3.1mg boric acid, 10.9mg sodium borate-1H₂O, 3.7mg disodium EDTA, 36.5mg sodium chloride, 1.0mg polyethylene glycol and 5.0mg cysteine.

42. The package of claim 41 formulated as a tablet.

43. The package of claim 41 wherein chymopapain is substituted for papain.

44. A composition for cleaning contact lenses comprising papain, (a heat stable buffer), disodium EDIA, sodium chloride, and cysteine.

45. The composition of claim 44 wherein said buffer system comprises boric acid and sodium borate.

46. The composition of claim 44 further comprising polyethylene glycol.

47. The composition of claim 44 wherein the papain is crystalline papain.

48. The composition of claim 44 wherein the papain is crude Prolase.

49. The composition of claim 44 wherein the papain is replaced with chymopapain.

50. The composition of claim 44 in tablet form.