Use of carbon dioxide and carbonic acid to clean contact lenses

Abstract

Simple, efficacious, easily manufacturable, convenient to use and cost-effective contact lens care cleaning compositions comprising carbon dioxide and carbonic acid as cleansing agents are disclosed. The compositions do not require abrasive agents such as polymeric beads, nor ocularly irritating agents such as enzymes or surfactants in order to effectively clean proteinaceous and nonproteinaceous deposits from the surface of contact lenses. Also disclosed is a one-step cleaning and disinfecting regimen, whereby an effervescent tablet composition capable of generating carbon dioxide and carbonic acid is dissolved in a disinfecting solution or rinsing/disinfecting/storage solution.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to contact lens cleaning methods and compositions. In particular, this invention relates to the use of carbon dioxide and carbonic acid to clean contact lenses.

2. Description of Related Art

Numerous contact lens care cleaning compositions are known. Contact lens cleaning products typically contain polymeric beads, enzymes, surfactants, or some combination thereof, as cleansing ingredients. Repeated use of cleaning compositions containing polymeric beads, such as Teflon or silicon dioxide beads, can damage the surface of contact lenses. Additionally, if all polymeric beads are not rinsed from the lens before inserting the lens in the eye, any residual beads may irritate the eye.

Enzymatic cleaners are popular cleansing agents for contact lenses, particularly for their ability to remove protein deposits. Raw material control for both enzymes and polymeric beads is often difficult. As in the case of polymeric beads, enzymes can be irritating to the eye if not thoroughly rinsed from the contact lens before it is inserted. Enzyme-containing cleaning products also suffer the disadvantage that they are generally incapable of being sterilized with heat, as the high temperatures required for sterilization can chemically degrade enzymes.

Surfactants are typically ineffective for cleaning protein deposits and are also generally irritating to the eye.

JP 01179123A (890717) discloses contact lens cleaning compositions containing percarbonate and an anionic or nonionic surfactant. The reaction of percarbonate with water generates oxygen bubbles. The reference attributes the cleaning to the mechanical cleaning action of the bubbles and the chemical cleaning action of the surfactant.

EP 93784A (831116) discloses enzymatic cleaning compositions for contact lenses. The cleaning compositions are comprised of an effervescent tablet containing trypsin, alpha-amylase, lipase, citric acid, sodium bicarbonate, calcium acetate and EDTA.

JP 88059123B (881117) discloses a foaming, contact lens cleaning tablet composition containing sodium bicarbonate, an organic or inorganic acid (or salt thereof), an enzyme, and a surfactant. When combined with clean water, the reference tablet foams, removing stains from the surface of contact lenses by the physical action of the foam. After foaming, remaining stains are removed by the enzyme and the surfactant.

Therefore, it is highly desirable to have lens care cleaning compositions which are capable of effectively cleaning proteinaceous and nonproteinaceous deposits from lenses, but which do not require the presence of polymeric beads, enzymes or cleansing amounts of surfactants.

SUMMARY OF THE INVENTION

The present invention provides contact lens care cleaning compositions comprising a cleansing amount of carbon dioxide and carbonic acid, or which are capable of generating a cleansing amount of carbon dioxide and carbonic acid. Because the compositions of the present invention do not require polymeric beads, enzymes or cleansing amounts of surfactants, they are much less likely to damage the surface of a contact lens or cause ocular irritation.

The present invention also provides a simple method of cleaning contact lenses. The method comprises contacting the lens in need of cleaning with carbon dioxide and carbonic acid for a time sufficient to achieve effective cleaning.

In the most preferred embodiment, the present invention provides a one-step cleaning and disinfecting system for contact lenses. A cleaning and disinfecting solution is prepared by dissolving an effervescent tablet in an ophthalmically acceptable disinfecting solution at a pH of less than about 7.5 such that carbon dioxide and carbonic acid are generated, and then the soiled contact lens is contacted with the resulting solution for a time sufficient to achieve effective cleaning and disinfection in a single step.

Among other factors, the present invention is based on the finding that soiled contact lenses can be effectively cleaned by compositions comprising a cleansing amount of carbon dioxide and carbonic acid, without the need for additional cleaning agents, such as polymeric beads, surfactants or enzymes, typically present in the contact lens care cleaning compositions currently marketed.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a comparison of the cleaning efficacy of cleaning solutions (with and without carbon dioxide).

DETAILED DESCRIPTION OF THE INVENTION

The contact lens cleaning compositions of the present invention comprise a cleansing amount of carbon dioxide and carbonic acid. Such compositions may contain carbon dioxide and carbonic acid in their final, packaged formulation, as in the case of compositions containing compressed carbon dioxide and water in a pressurized container. For example, carbon dioxide could be used as the pressurizing gas in an aerosol can containing purified water, a simple contact lens storage solution, or an aqueous-based multi-purpose contact lens composition, including the commercially available rinsing, disinfecting and storage solutions known as Opti-Free or Opti-One Express.

Alternatively, the compositions of the present invention may be formulated to generate carbon dioxide and carbonic acid to clean contact lenses. For example, effervescent tablets may be prepared which, upon dissolution in water or saline solution at a pH of less than about 7.5, generate a cleansing amount of carbon dioxide and carbonic acid. Compositions of the latter type are preferred for their consumer convenience, ease of manufacture, simple packaging requirements and cost.

Other ways to generate carbon dioxide and carbonic acid are possible. For example, an acidic composition can be packaged separately from an aqueous solution containing a carbonate compound. When a drop or two of the acidic composition is added to a contact lens storage case pre-filled with the aqueous solution containing a carbonate compound, carbon dioxide and carbonic acid would be generated.

A less convenient, but still effective method of adding carbon dioxide and carbonic acid into a contact lens storage case involves packaging an aqueous composition (e.g., purified water or a buffered, isotonic composition, such as Opti-Free or Opti-One Express) containing dissolved carbon dioxide in a polyethylene terephthalate (PET) bottle under pressure, much like soft drinks are packaged in PET bottles. Once the cap is removed from the bottle, the carbon dioxide composition can be combined in a suitable container with a contact lens for cleaning. After replacing the bottle cap, the dissolved carbon dioxide will escape from the bottle. PET bottles containing dissolved carbon dioxide for this use will, therefore, likely contain only enough product for one cleaning or a “single-use.”

Still another way to generate carbon dioxide and carbonic acid in a lens case involves combining an aqueous buffered, isotonic, preserved solution containing a carbonate component with heat and/or a metal catalyst fixed in the lens case. For example, a metal catalyst coating on the walls of the lens storage case would react with the carbonate from the aqueous buffered, isotonic, preserved solution to produce carbon dioxide and carbonic acid.

Because the compositions of the present invention do not require enzymes to effectively clean soiled contact lenses, they may be sterilized using conventional gamma irradiation sterilization techniques. When combined with a disinfecting solution or a rinsing, disinfecting and storage solution, the burden upon the disinfectant is lower in the case of the cleaning compositions of the present invention than in the case of conventional enzyme-containing cleaning compositions.

In a preferred embodiment of the present invention, the composition of the present invention is prepared in the form of an effervescent tablet. As those skilled in art appreciate, the effervescent tablet must contain a basic component and an acidic component, so that upon dissolution appropriate reactions occur to generate carbon dioxide and carbonic acid. If the tablet does not directly contain both acidic and basic components, it may be formulated with just one of these ingredients, with the other ingredient added by way of the diluent composition. In this way, in the event the tablet is exposed to moisture during storage, for example, premature acid-base reactions can be minimized or avoided. Suitable effervescent components include the carbonate family of basic compounds and inorganic or organic acidic compounds. The effervescent tablet can be formulated as a layered tablet, with one layer comprising the acidic component and the other the basic component, in order to minimize premature acid-base reactions during storage.

Among the carbonate family of basic compounds, preferred effervescent components for use in the compositions of the present invention are sodium carbonate, sodium bicarbonate, glycine carbonate, potassium carbonate, potassium bicarbonate, potassium dihydrogencitrate, and calcium carbonate. Most preferred is sodium bicarbonate.

Preferred acidic components for use in the compositions of the present invention are citric acid, adipic acid, tartaric acid, maleic acid, boric acid, benzoic acid, hydroxybenzoic acid, methoxybenzoic acid, mandelic acid, malonic acid, lactic acid, pyruvic acid, glutaric acid, aspartic acid, hydrochloric acid, oxalic acid, salicylic acid, succinic acid, and acetic acid. The most preferred acidic effervescent components are citric acid and adipic acid, and combinations of these two acids.

As those skilled in the art appreciate, the amounts of the basic and acidic components required in the compositions of the present invention to generate an amount of carbon dioxide and carbonic acid sufficient to clean a soiled contact lens will depend on a number of factors, including the particular basic and acidic components chosen, the period of time available for cleaning, the type and extent of the deposits on the soiled lens to be cleaned, etc. Generally, however, the amount of carbon dioxide required will be at least 5 mg or more.

In the case of sodium bicarbonate and citric acid, the amount of the basic component will typically be from 10 to 200 mg, and the amount of the acidic component will typically be from 5 to 65 mg. Particularly if acidic and basic component concentrations in the lower portion of these ranges are employed, additional ingredients, such as sodium chloride, mannitol, sorbitol, glucose, fructose or lactose, can be added to the basic and acidic effervescent components as fillers, excipients, bulking agents or tonicity agents.

Without being bound to any theory, it is believed that CO 2 produced from the reaction between the acidic and basic effervescent components of the tablet compositions of the present invention in the presence of water generates carbonic acid.

In some cases, it is desirable to include a lubricant in effervescent tablet compositions in order to facilitate the manufacture of tablets. Suitable lubricants and their typical concentrations (in weight percent based on total tablet composition) include polyethylene glycol 3,350 (0.05-10%); polyethylene glycol 8,000 (1-10%); sodium benzoate (1-10%); vegetable oils (1-4%); talc (1-5%); boric acid (0.5-5%); and sodium borate (0.5-5%). The preferred lubricant for use in the tablet compositions of the present invention is polyethylene glycol 3,350.

In addition to the basic and acidic effervescent tablet ingredients described above, the tablet composition of the present invention may also contain other excipients conventionally employed in ophthalmic tablet compositions such as lactose anhydrous, lactose, mannitol, sorbitol, glucose, fructose; compressible sugar; or sodium chloride. Sodium chloride can be used to adjust the tonicity of the tablet in order to cause the solution resulting from the dissolution of the tablet to be isotonic. Though it is not an essential ingredient, the preferred tablet compositions of the present invention may contain lactose anhydrous as a filler. As mentioned above, however, the tablet compositions do not contain polymeric beads, an enzyme, or cleansing amounts of surfactants. The compositions do not contain a disinfecting amount of hydrogen peroxide.

The tablet compositions of the present invention are obtained using tableting procedures known in the art. Generally, the tableting procedures may be summarized as follows.

1. The formulation ingredients are weighed and sized using an oscillating granulator with an 18 to 40 mesh screen (may use any of 18, 20, 26, 30, 33 or 40 mesh screen).

2. The materials are then blended using a twin shell P-K blender until uniform (generally about 30 minutes or less). Alternatively, a cone blender may be used.

3. Tablets are compressed using suitable tooling on a suitable tablet press.

4. Tablet weight can be adjusted from about 35 to 300 mg (a preferred tablet weight is about 73 mg).

5. The tablet hardness ranges from 2 to 8 strong cobb units.

6. Tablets are then pressed and strip packaged.

7. The strip packaged tablets can then be sterilized using γ (gamma) irradiation.

The effervescent tablet compositions of the present invention may be is dissolved in purified water or a simple saline solution in a contact lens holder (such as a 5 mL plastic vial). The soiled contact lens may be placed in the lens holder containing purified water or saline solution prior to, or just after, the effervescent tablet is added to the holder. Once the tablet is dissolved, typically in about 60 seconds or less, the soiled contact lens is contacted with the resulting solution for a time sufficient to achieve effective cleaning. The pH of the resulting solution is less than about 7.5. The time required for effective cleaning will vary depending upon the type and extent of deposits on the lens, etc., but is generally less than about 4 hours and preferably less than about 1 hour.

In one embodiment, the present invention provides a method of cleaning contact lenses comprising dissolving a tablet consisting essentially of a basic effervescent component and an acidic effervescent component in an aqueous composition at a pH of less than about 7.5 such that a cleansing amount of carbon dioxide and carbonic acid are produced and contacting the contact lens with the carbon dioxide and carbonic acid, wherein the tablet optionally contains one or more ingredients selected from the group consisting of fillers, lubricating agents, bulking agents and tonicity agents, but does not contain polymeric beads, an enzyme, a cleansing amount of a surfactant, or a disinfecting amount of hydrogen peroxide.

Alternatively, a simple, one-step cleaning and disinfecting regimen is obtained when the effervescent tablet compositions of the present invention are dissolved in an aqueous composition selected from the group consisting of disinfecting solutions and rinsing/disinfecting/storage solutions, instead of a purified water or a simple saline solution as described above. Suitable disinfectants include polyquaternium-1, the disinfectant contained in Opti-Free® Rinsing, Disinfecting & Storage Solution, but do not include hydrogen peroxide. Accordingly, the compositions of the present invention do not include a disinfecting amount (e.g., about 0.01 to less than 0.5% w/v) of hydrogen peroxide, nor are they combined with aqueous compositions comprising a disinfecting amount of hydrogen peroxide.

The following examples are presented to illustrate various aspects of the present invention, but are not intended to limit the scope of the invention in any respect.

Tableting Procedure: All tablets referred to in the examples presented below were prepared according to the following procedure in 20% or lower humidity conditions:

a) The formulation ingredients were weighed, sized using an oscillating granulator with a suitable mesh screen (18-40 mesh), and blended using a twin shell Patterson-Kelly blender for 30 minutes.

b) Tablets were compressed using a {fraction (3/16)}″ diameter tablet tooling on a Stokes B-2 tablet press.

c) The tablets weighed an average of 73 mg/tablet, with a hardness of about 5.0-7.0 Strong Cobb Units.

d) Tablet disintegration time was measured in purified water and found to be about 35-45 seconds for each of the tablets mentioned in Examples 1 and 2.

Cleaning Efficacy

Cleaning efficacy was determined using soiled contact lenses. Soiled lenses were obtained from two sources: (1) human study participants (“human-worn lenses”) and (2) a laboratory where lysozyme, mucin and lipids were intentionally deposited upon the lenses (“laboratory deposited lenses”).

Cleanliness of the lenses was evaluated as follows. The loosely-bound deposits on soiled lenses were removed by gently rubbing both surfaces of the lenses with Unisol Plus® saline solution in the palm of a hand. The lenses were then visually examined for remaining deposits and rated according to the Rudko system for classification of lens deposits. See Table 1 below (Equipment: Bausch and Lomb tweezers; Bausch and Lomb spotlight; Sorgs lint-free towel; and Vigor measuring magnifier 7X#EL470).

TABLE 1
Rudko Lens Deposit Classification System
Class
    Heaviness of Deposit
I   Clean
II  Visible under oblique light when wet or dry
    using 7× magnification
III Visible when dry with the unaided eye
IV  Visible when wet with the unaided eye
    Type of Deposit
C   Crystalline
G   Granular
F   Filmy
    Extent of Deposit
A   0-25% of lens
B   25-50% of lens
C   50-75% of lens
D   75-100% of lens
Definitions
C: Crystalline deposits comprised of crystal groups which may be scattered or layered and are usually iridescent, depending upon the illumination.
G: Granular deposits consisting of fine granulation, usually in mass form.
F: Film and hazes consisting of castings which are not granular or crystalline. The hazes often have a bluish tint.

After their initial cleanliness evaluation, the lenses were soaked in the designated cleaning solution for the indicated period of time (30, 60, 120 or 240 minutes) and again rated for deposits according to the cleanliness evaluation system described above. The lenses which were not cleaned after 1 hour were exposed to same cleaning solution for additional time (2 and 4 hrs), and rated again.

EXAMPLE 1

Preparation of Citric Acid/Sodium Bicarbonate Tablets

Effervescent tablets were formulated according to the procedures described above using following ingredients:

		Gm/10,000
Ingredients	mg/Tablet	Tablets
*Citric Acid, USP, Anhydrous	21.0	210.0
*Sodium Bicarbonate, USP, Powder	48.0	480.0
**Polyethylene Glycol, 3350, USP,	4.0	40.0
Fine Powder
Total	73.0***	730.0
*Effervescent components
**Tablet Lubricant
***Theoretically, 73 mg effervescent tablet gives 25 mg of carbon dioxide

EXAMPLE 2

Preparation of Adipic Acid/Sodium Bicarbonate Tablets

Effervescent tablets were formulated according to the procedures described above using following ingredients:

		Gm/10,000
Ingredients	mg/Tablet	Tablets
*Adipic Acid, N.O.C.	38.6	386
*Sodium Bicarbonate, USP, Powder	34.4	344
Total	73.0**	730.0
*Eftervescent components
**Theoretically, 73 mg eftervescent tablet gives 25 mg of carbon dioxide

EXAMPLE 3

Preparation of Sodium Citrate Solution

A cleaning solution was formulated using following ingredients:

Ingredients    amount
Sodium Citrate 2 g
Purified Water q.s. to 100 mL

EXAMPLE 4

Disintegration Time and Solution pH for Tablets of Example 1

The disintegration time and pH of solution were determined after dissolving one and two tablets of Example 1, respectively, in separate vials each containing 5 mL of purified water. The results are shown in Table 2 below.

TABLE 2
1 Tablet in 5 mL Diluent	2 Tablets in 5 mL Diluent
Observ-			Observ-
ation	Disintegration		ation	Disintegration
#	Time (sec)	pH	#	Time (sec)	pH
1	35	6.65	1	35, 35	6.54
2	36	6.43	2	38, 40	6.50
3	37	6.63	3	42, 42	6.53
4	40	6.37	4	40, 42	6.54
5	40	6.38	5	40, 40	6.55

EXAMPLE 5

Cleaning Efficacy of Tablets of Example 1 (1 Tablet/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets of Example 1 was evaluated by placing one 73 mg tablet into 5 mL of diluent (purified water). Theoretically, a 73 mg tablet gives 25 mg of carbon dioxide. After the tablet was dissolved, soiled human worn soft contact lenses were rated and placed in the solution. After soaking in the solution for one hour, the lenses were rated again. If the lens was not cleaned after one hour, the lens was returned to the solution for an additional hour. If the lens was not cleaned after the second hour, the lens was returned to the solution for an additional two hours and evaluated again. Eight soft contact lenses were evaluated. The results are presented below in Table 3.

TABLE 3
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(1 Tablet/5 mL Diluent)
With Soiled Human Worn Soft Contact Lenses
	Cleanliness Rating
	Before	After Cleaning
Lens #	Lens Type	Lens Age	Cleaning	1 Hr	2 Hr	4 Hr
1	Group II	2 years	III FA	III FA	I	—
2	Group II	2 years	III FC	III FA	I	—
3	Group II	6 months	III FC	III FA	I	—
4	Group II	6 months	III FB	III FA	III FA	I
5	Group IV	8 months	III FC	III FC	I	—
6	Group IV	8 months	III FB	III FB	I	—
7	Group IV	6 months	III FA	III FA	I	—
8	Group IV	6 months	III FA	III FA	I	—

EXAMPLE 6

Cleaning Efficacy of Tablets of Example 1 (2 Tablets/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets of Example 1 was evaluated as described in Example 5 above, except that in this case two 73 mg tablets were placed into 5 mL of diluent (purified water). Theoretically, two 73 mg tablets give 50 mg of carbon dioxide. Twelve soft contact lenses were evaluated. The results are shown in Table 4 below.

TABLE 4
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(2 Tablets/5 mL Diluent)
With Soiled Human Worn Soft Contact Lenses
	Cleanliness Rating
	Lens	Before	After Cleaning
Lens #	Type	Lens Age	Cleaning	1 Hr	2 Hr	4 Hr
1	Group IV	6 months	III FC	III FA	I	—
2	Group IV	6 months	III FB	I	—
3	Group I	6 months	III FC	III FA	I	—
4	Group I	6 months	III FB	III FA	I	—
5	Group IV	2 months	IV FD	I	—
6	Group IV	2 months	IV FD	I	—
7	Group I	6 months	III FA	I	—
8	Group I	6 months	III FC	I	—
9	Group I	12 months	III FA	III FA	I	—
10	Group I	12 months	III FA	I	—
11	Group IV	6 months	III FB	I	—
12	Group IV	6 months	III FB	I	—

EXAMPLE 7

Cleaning Efficacy of Tablets of Example 1 (3 Tablets/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets of Example 1 was evaluated as described in Example 5 above, except that in this case three 73 mg tablets were placed into 5 mL of diluent (purified water). Theoretically, three 73 mg tablets give 75 mg of carbon dioxide. Four soft contact lenses were evaluated. The results are shown in Table 5 below.

TABLE 5
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(3 Tablets/5 mL Diluent)
With Soiled Human Worn Soft Contact Lenses
	Cleanliness Rating
	Lens	Lens	Before	After Cleaning
Lens #	Type	Age	Cleaning	1 Hr	2 Hr	4 Hr
1	Group I	6 months	III FA	I	—
2	Group I	6 months	III FC	I	—
3	Group I	6 months	III FD	I	—
4	Group I	6 months	III FB	I	—

EXAMPLE 8

Cleaning Efficacy of Tablets of Example 1 (1 Tablet/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets of Example 1 was evaluated as described in Example 5 above, except that in this case six soiled human worn rigid gas permeable contact lenses were evaluated. The results are shown in Table 6 below.

TABLE 6
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(1 Tablet/5 mL Diluent)
With Soiled Human Worn Rigid Gas Permeable Lenses
	Cleanliness Rating
	Lens		Before	After Cleaning
Lens #	Type	Lens Age	Cleaning	1 Hr	2 Hr	4 Hr
1	RGP	12 months	III FB	III FA	I	—
2	RGP	6 months	III FC	I	—
3	RGP	6 months	III FD	I	—
4	RGP	6 months	III FA	I	—
5	RGP	3 months	III FA	I	—
6	RGP	3 months	III FA	I	—

EXAMPLE 9

Cleaning Efficacy of Tablets of Example 1 (2 Tablets/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets of Example 1 was evaluated as described in Example 6 above, except that in this case soiled human worn rigid gas permeable contact lenses were evaluated. Four lenses were evaluated. The results are shown in Table 7 below.

TABLE 7
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(2 Tablets/5 mL Diluent)
With Soiled Human Worn Rigid Gas Permeable Lenses
	Cleanliness Rating
	Lens		Before	After Cleaning
Lens #	Type	Lens Age	Cleaning	1 Hr	2 Hr	4 Hr
1	RGP	6 months	III FA	I	—
2	RGP	12 months	III FA	I	—
3	RGP	12 months	III FA	I	—
4	RGP	12 months	III FA	I	—

EXAMPLE 10

Cleaning Efficacy of Tablets of Example 2 (2 Tablets/5 mL Diluent)

The cleaning efficacy of the adipic acid/sodium bicarbonate tablets of Example 2 was evaluated by placing two 73 mg tablets into 5 mL of diluent (Unisol Plus Saline Solution). Theoretically, two 73 mg tablets give 50 mg of carbon dioxide. After the tablets dissolved, soiled human worn soft contact lenses or laboratory deposited soft contact lenses were placed in the solution and evaluated after soaking for one hour. Ten lenses were evaluated. After one hour of soaking, all ten lenses were effectively cleaned. The results are presented below in Table 8.

TABLE 8
Cleaning Efficacy of Adipic Acid/Sodium Bicarbonate Tablets
(2 Tablets/5 mL Diluent)
With Soiled Human Worn and Laboratory Deposited Soft Contact Lenses
	Cleanliness Rating
Lens	Before Cleaning	After Cleaning
#	Initial	30 Min	60 Min	120 Min
Human Worn Soft Lenses
5	IIIFB	IIIFA	I	—
6	IIIFA	IIIFA	I	—
7	IIIFB	IIIFA	I	—
8	IIIFB	IIIFA	I	—
24	IVFC	IIIFB	I	—
25	IVFC	IIIFA	I	—
26	IVFD	IIIFB	I	—
Laboratory Deposited Soft Lenses
1	IVFD	IIIFA	I	—
2	IVFD	IIIFB	I	—
3	IVFC	IIIFA	I	—

EXAMPLE 11

Cleaning Efficacy of Tablets of Example 2 (with CO 2 removed from solution)

The experiment of Example 10 above was repeated, except that the CO 2 was removed from the solution prior to exposing the soiled lenses to the solution. Cleaning solutions were prepared by dissolving two tablets of Example 2 in 5 mL of Unisol Plus Saline Solution. The cleaning solutions were then heated in a microwave oven at low setting for 2 minutes to remove CO 2 . The soiled lenses (human worn and lab deposited) were then soaked in the cleaning solution for the designated time and rated. The results, shown below in Table 9, for the eight lenses evaluated show no cleaning after 120 minutes.

TABLE 9
Cleaning Efficacy of Adipic Acid/Sodium Bicarbonate Tablets
(After CO 2 Removed)
With Soiled Human Worn and Laboratory Deposited Soft Contact Lenses
	Cleanliness Rating
Lens	# of	Before Cleaning	After Cleaning
#	Tablets	Initial	30 Min	60 Min	120 Min
Human Worn Soft Lenses
9	2	IVFD	IVFD	IVFD	IVFD
10	2	IIIFB	IIIFB	IIIFB	IIIFB
11	2	IIIFA	IIIFA	IIIFA	IIIFA
12	2	IIIFA	IIIFA	IIIFA	IIIFA
30	2	IVFC	IVFC	IVFC	IVFC
31	2	IVFD	IVFD	IVFD	IVFD
Laboratory Deposited Soft Lenses
9	2	IVFD	IVFD	IVFD	IVFD
10	2	IVFD	IVFD	IVFD	IVFD

EXAMPLE 12

Cleaning Efficacy of Tablets of Example 1 in Saline Solution (2 Tablets/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets of Example 1 was evaluated as described in Example 6 above, except that in this case the cleaning solutions were prepared by dissolving two tablets of Example 1 in 5 mL of diluent (Unisol Plus Saline Solution). A total of ten soiled (human worn and laboratory deposited) soft contact lenses were evaluated. The results are shown in Table 10 below. All ten lenses were cleaned within 60 minutes.

TABLE 10
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(2 Tablets/5 mL Diluent)
With Soiled Human Worn Contact Lenses
	Cleanliness Rating
Lens	# of	Before Cleaning	After Cleaning
#	Tablets	Initial	30 Min	60 Min	120 Min
Human Worn Soft Lenses
1	2	IIIFA	IIIFA	I	—
2	2	IIIFA	IIIFA	I	—
3	2	IIIFB	IIIFA	I	—
4	2	IIIFB	IIIFA	I	—
27	2	IVFC	IIIFA	I	—
28	2	IVFD	IIIFB	I	—
29	2	IVFD	IIIFA	I	—
Laboratory Deposited Soft Lenses
4	2	IVFD	IIIFA	I	—
5	2	IVFD	IIIFA	I	—
6	2	IVFC	IIIFA	I	—

EXAMPLE 13

Cleaning Efficacy of Tablets of Example 1 (with CO 2 removed from solution)

The experiment of Example 12 above was repeated, except that the CO 2 was removed from the cleaning solution prior to exposing the soiled lenses to the solution. Cleaning solutions were prepared by dissolving two tablets of Example 1 in 5 mL of Unisol Plus Saline Solution. The cleaning solutions were then heated in a microwave oven at low setting for 2 minutes to remove CO 2 . The soiled lenses (human worn and lab deposited) were then soaked in the cleaning solution for the designated time and rated. The results, shown below in Table 11, for the eight lenses evaluated show essentially no cleaning after 120 minutes.

TABLE 11
Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets
(After CO 2 Removed)
With Soiled Human Worn and Laboratory Deposited Soft Contact Lenses
	Cleanliness Rating
Lens	# of	Before Cleaning	After Cleaning
#	Tablets	Initial	30 Min	60 Min	120 Min
Human Worn Soft Lenses
13	2	IIIFB	IIIFB	IIIFB	IIIFB
14	2	IIIFB	IIIFB	IIIFB	IIIFA
15	2	IIIFB	IIIFB	IIIFB	IIIFB
16	2	IIIFB	IIIFB	IIIFB	IIIFB
32	2	IVFD	IVFB	IVFD	IVFD
33	2	IVFC	IVFB	IVFB	IVFB
Laboratory Deposited Soft Lenses
7	2	IVFC	IVFC	IVFC	IVFC
8	2	IVFD	IVFD	IVFD	IVFD

EXAMPLE 14

Cleaning Efficacy of Sodium Citrate Solution of Example 3

The cleaning efficacy of the cleaning solution of Example 3 was evaluated as follows. Eleven soiled lenses (human worn) were rated for deposits, then soaked in the cleaning solution for the designated time and rated again. The results, shown below in Table 12 show no effective cleaning after 120 minutes.

TABLE 12
Cleaning Efficacy of Sodium Citrate Solution
With Soiled Human Worn Soft Contact Lenses
		Cleanliness Rating
	Lens	Before Cleaning	After Cleaning
	#	Initial	30 Min	60 Min	120 Min
	Human Worn Soft Lenses
	17	IIIFB	IIIFB	IIIFB	IIIFB
	18	IIIFB	IIIFB	IIIFB	IIIFB
	19	IVFD	IVFD	IVFC	IVFC
	20	IIIFB	IIIFB	IIIFB	IIIFB
	21	IIIFB	IIIFB	IIIFB	IIIFB
	22	IIIFB	IIIFB	IIIFB	IIIFB
	23	IIIFA	IIIFA	IIIFA	IIIFA
	1A	IIIFC	IIIFC	IIIFC	IIIFC
	2A	IIIFB	IIIFB	IIIFB	IIIFB
	3A	IVFD	IIIFD	IIIFD	IIIFD
	4A	IVFC	IVFC	IVFC	IVFC

EXAMPLE 15

Recleaning of Laboratory Deposited Soft Lenses with Tablet of Example 1

Soiled (laboratory deposited) lenses #7 and #8 (Table 11) in Example 13 above which were not cleaned when exposed to a cleaning solution prepared by dissolving two tablets of Example 1 in 5 mL of Unisol Plus Saline Solution and then eliminating the CO 2 by heating in a microwave oven on a low setting for two minutes, were recleaned by subjecting them to a cleaning solution prepared by dissolving one tablet of Example 1 in 5 mL of Unisol Plus Saline Solution. As shown in Table 13 below, both lenses were effectively cleaned after 120 minutes. This experiment demonstrates that the presence of CO 2 is necessary for effective cleaning of soiled lenses.

TABLE 13
Recleaning of Soiled (Laboratory Deposited) Soft Contact Lenses Using
Tablet of Example 1 (1 Tablet/5 mL Diluent).
	Cleanliness Rating
	Before
Lens	Cleaning	After Cleaning
#	Initial	30 Min	60 Min	120 Min
7	IVFC	IIIFC	IIIFC	I
8	IVFD	IIIFB	IIIFB	I

EXAMPLE 16

Recleaning of Laboratory Deposited Soft Lenses with Tablet of Example 2

Soiled (laboratory deposited) lenses #9 and #10 (Table 9) in Example 11 above which were not cleaned when exposed to a cleaning solution prepared by dissolving two tablets of Example 2 in 5 mL of Unisol Plus Saline Solution and then eliminating the CO 2 by heating in a microwave oven on a low setting for two minutes, were recleaned by subjecting them to a cleaning solution prepared by dissolving one tablet of Example 2 in 5 mL of Unisol Plus Saline Solution. As shown in Table 14 below, both lenses were effectively cleaned after 120 minutes. This experiment demonstrates that the presence of CO 2 is necessary for effective cleaning of soiled lenses.

TABLE 14
Recleaning of Soiled (Laboratory Deposited) Soft Contact Lenses Using
Tablet_of Example 2 (1 Tablet/5 mL Diluent).
	Cleanliness Rating
	Before
Lens	Cleaning	After Cleaning
#	Initial	30 Min	60 Min	120 Min
9	IVFD	IIIFD	IIIFA	I
10	IVFD	IIIFB	IIIFB	I

EXAMPLE 17

Recleaning of Human Worn Soft Lenses with Tablet of Example 1

Soiled (human worn) lenses #17-22 (Table 12) in Example 14 above which were not cleaned when exposed to the sodium citrate cleaning solution of Example 3, were recleaned by subjecting to them to a cleaning solution prepared by dissolving two tablets of Example 1 in 5 mL of Unisol Plus Saline Solution. As shown in Table 15 below, most lenses were effectively cleaned after 60 minutes and all lenses were effectively cleaned after 120 minutes. This experiment demonstrates that the presence of CO 2 is necessary for effective cleaning of soiled lenses.

TABLE 15
Recleaning of Soiled (Human Worn) Soft Contact Lenses Using
Tablet of Example 1 (2 Tablet/5 mL Diluent).
	Cleanliness Rating
	Before
Lens	Cleaning	After Cleaning
#	Initial	30 Min	60 Min	120 Min
17	IIIFD	IIIFA	I	—
18	IIIFB	IIIFA	I	—
19	IVFD	IIIFC	IIIFA	I
20	IIIFB	IIIFA	I	—
21	IIIFB	IIIFA	I	—
22	IIIFB	IIIFA	I	—

EXAMPLE 18

Recleaning of Human Worn Soft Lenses with Tablet of Example 2

Soiled (human worn) lenses #23 and 1A-4A (Table 12) in Example 14 above which were not cleaned when exposed to the sodium citrate cleaning solution of Example 3, were recleaned by subjecting them to a cleaning solution prepared by dissolving two tablets of Example 2 in 5 mL of Unisol Plus Saline Solution. As shown in Table 15 below, most lenses were effectively cleaned after 60 minutes and all lenses were effectively cleaned after 120 minutes. This experiment demonstrates that the presence of CO 2 is necessary for effective cleaning of soiled lenses.

TABLE 16
Recleaning of Soiled (Human Worn) Soft Contact Lenses Using
Tablet of Example 2 (2 Tablet/5 mL Diluent).
	Cleanliness Rating
	Before
Lens	Cleaning	After Cleaning
#	Initial	30 Min	60 Min	120 Min
23	IIIFA	I	—	—
1A	IIIFC	IIIFC	IIIFC	I
2A	IIIFB	IIIFA	I	—
3A	IIIFD	IIIFA	I	—
4A	IVFC	IIIFB	I	—

EXAMPLE 19

Normalization of Cleaning Data for Human Worn Soft Contact Lenses #17-22

For comparison purposes, the cleaning results for soiled (human worn) soft contact lenses #17-22 in Table 12 were normalized with the data in Table 15. In order to plot the cleaning efficacy data against time, the lens deposit rating obtained using the Rudko rating system (Tables 12 and 15) was converted to a numerical rating using the conversion key shown below in Table 17. The number assigned for each Rudko rating for each lens was added for each time interval and the data normalized by dividing with highest number. The normalized data for cleaning efficacy with 2% Sodium Citrate Solution of Example 3 and cleaning efficacy with the citric acid/sodium bicarbonate tablets of Example 1 appears in Table 18 below and is summarized in FIG. 1 . This normalized data illustrates that complete, effective cleaning was achieved with the CO 2 -containing solution in two hours. However, most of the lenses were cleaned in one hour. In the absence of carbon dioxide, no cleaning was achieved. This is also evident from the data shown in Table 11.

TABLE 17
Rudko Lens Deposit Classification System
Conversion of Rudko Deposit Classification to Numerals
Rudko Classification Numeral Assigned
I - Clean Lens       0.00
IIFA                 1.25
IIFB                 1.50
IIFC                 1.75
IIFD                 2.00
IIIFA                2.25
IIIFB                2.50
IIIFC                2.75
IIIFD                3.00
IVFA                 3.25
IVFB                 3.50
IVFC                 3.75
IVFD                 4.00

TABLE 18
Numerical Equivalent of Rudko Rating for Cleaning Efficacy Data
(Human Worn Lenses #17-22)
Lens	Before Cleaning	After Cleaning
#	Initial	30 Min	60 Min	120 Min
Data from Table 12 (Without CO 2 )
17	2.50	2.50	2.50	2.50
18	2.50	2.50	2.50	2.50
19	4.00	4.00	3.75	3.75
20	2.50	2.50	2.50	2.50
21	2.50	2.50	2.50	2.50
22	2.50	2.50	2.50	2.50
Total	16.50	16.50	16.25	16.25
Normalized	1.00	1.00	0.985	0.985
Data from Table 15 (With CO 2 )
17	2.50	2.25	0.0	—
18	2.50	2.25	0.0	—
19	4.00	2.75	2.25	0.0
20	2.50	2.25	0.0	0.0
21	2.50	2.25	0.0	0.0
22	2.50	2.25	0.0	0.0
Total	16.50	14.00	2.25	0.0
Normalized	1.00	0.848	0.136	0

EXAMPLE 20

Osmolality and pH Measurements

Fresh samples of various cleaning solutions were prepared and their osmolality and pH determined. Osmolality and pH of Unisol Plus were also determined as a control. The data is shown below in Table 19.

TABLE 19
Osmolality and pH Measurements
		Osmolality
#	Sample	mOsm/Kg	pH
1.	Unisol Plus Saline Solution	300	7.38
2.	2% Sodium Citrate in Purified Water (Ex. 3)	186	7.85
3.	Two Adipic Acid Based Tablets (Ex. 2)	568	5.32
	dissolved in 5 mL of Unisol Plus
4.	Two Citric Acid Based Tablets (Ex. 1)	616	7.02
	dissolved in 5 mL of Unisol Plus
5.	One Adipic Acid Based Tablet (Ex. 2)	441	5.33
	dissolved in 5 mL of Unisol Plus
6.	One Citric Acid Based Tablet (Ex. 1)	461	7.09
	dissolved in 5 mL of Unisol Plus
7.	Two Adipic Acid Based Tablets (Ex. 2)	637	5.16
	dissolved in 5 mL of Unisol Plus and
	heated to remove CO 2
8.	Two Citric Acid Based Tablets (Ex. 1)	646	8.11
	dissolved in 5 mL of Unisol Plus and
	heated to remove CO 2

The invention has been described by reference to certain preferred embodiments; however, it should be understood that it may be embodied in other specific forms or variations thereof without departing from its spirit or essential characteristics. The embodiments described above are therefore considered to be illustrative in all respects and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description.

Claims

1. A method of cleaning a soiled contact lens comprising the steps of dissolving an effervescent tablet composition capable of generating a cleansing amount of carbon dioxide and carbonic acid in an aqueous composition having a pH of less than about 7.5 to form a cleaning solution, and contacting the soiled lens with the cleaning solution for a time sufficient to clean the soiled lens, wherein the effervescent tablet composition excludes polymeric beads, an enzyme, a cleansing amount of a surfactant, and a disinfecting amount of hydrogen peroxide, and further provided that the effervescent tablet is a layered tablet comprising a first layer containing a compound selected from the group consisting of alkali carbonate compounds but lacking an acidic compound and a second layer containing a compound selected from the group consisting of organic and inorganic acidic compounds but lacking an alkali carbonate compound.

2. The method of claim 1 wherein the first layer comprises an alkali carbonate compound selected from the group consisting of sodium carbonate, sodium bicarbonate, glycine carbonate, potassium carbonate, potassium bicarbonate, potassium dihydrogencitrate, and calcium carbonate; and the second layer comprises a compound selected from the group consisting of citric acid, adipic acid, tartaric acid, maleic acid, boric acid, benzoic acid, hydroxybenzoic acid, methoxybenzoic acid, mandelic acid, malonic acid, lactic acid, pyruvic acid, glutaric acid, aspartic acid, hydrochloric acid, oxalic acid, salicylic acid, succinic acid, and acetic acid.

3. The method of claim 2 wherein the first layer comprises sodium bicarbonate and the second layer comprises an acidic compound selected from the group consisting of citric acid, adipic acid and combinations of citric and adipic acids.

4. The method of claim 1 wherein the aqueous composition is selected from the group consisting of purified water; saline solutions; disinfecting solutions; and rinsing/disinfecting/storage solutions; provided that the aqueous composition does not contain a disinfecting amount of hydrogen peroxide.

5. A method of cleaning a soiled contact lens comprising the steps of dissolving an effervescent tablet composition in an aqueous composition having a pH of less than about 7.5 to form a cleaning solution, and contacting the soiled lens with the cleaning solution for a time sufficient to clean the soiled lens, wherein the effervescent tablet composition excludes polymeric beads, an enzyme, a cleansing amount of a surfactant, and a disinfecting amount of hydrogen peroxide, and further provided that only one of the effervescent tablet and the aqueous composition contains an alkali carbonate compound but no acidic component, and the other of the effervescent table and the aqueous composition contains an acidic component but no alkali carbonate compound, such that when the effervescent tablet is dissolved in the aqueous composition a cleansing amount of carbon dioxide and carbonic acid is generated.

6. A method of cleaning a soiled contact lens comprising contacting the soiled lens with an aqueous composition having a pH of less than about 7.5 comprising a cleansing amount of carbon dioxide and carbonic acid for a time sufficient to clean the soiled lens, wherein the composition excludes polymeric beads, an enzyme, a cleansing amount of a surfactant, and a disinfecting amount of hydrogen peroxide, and wherein the composition is formed by combining separately packaged first and second aqueous compositions, where the first aqueous composition comprises an alkali carbonate compound but lacks an acidic component selected from the group consisting of inorganic and organic acids, and the second aqueous composition comprises an acidic component selected from the group consisting of inorganic and organic acids but lacks an alkali carbonate compound.