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Claims  |
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What is claimed is:
1. A process for disinfecting a contact lens, comprising
(A) immersing the lens in a predetermined volume of an aqueous disinfecting
solution consisting essentially of H.sub.2 O.sub.2 at a concentration of
about 3 wt. % or less which is effective to disinfect the lens in a
disinfection period of less than about 6 hours, and
(B) decomposing the H.sub.2 O.sub.2 in said disinfecting solution by adding
to said solution, before said disinfection period has elapsed, a
neutralizer in the form of a tablet or a plurality of particles and
comprising
one or more H.sub.2 O.sub.2 -neutralizing compounds which react with
H.sub.2 O.sub.2 to form H.sub.2 O and reaction products which are
non-injurious to the eye, in an amount of said one or more compounds
effective to react with all the H.sub.2 O.sub.2 in said solution, and
thereby to form an aqueous solution containing said reaction products and
having a pH of 6.5 to 8.5 and a tonicity of 200 to 450 milliosmol per kg
of solution, and
a coating encasing said tablet or each of said particles which coating
dissolves gradually in said H.sub.2 O.sub.2 solution, so as to release
said one or more H.sub.2 O.sub.2 -neutralizing compounds only after said
disinfection period has elapsed,
whereby said released neutralizing compounds transform said H.sub.2 O.sub.2
solution in situ into a buffered, saline lens storage solution.
2. The process of claim 1 wherein said disinfection period is less than
about 3 hours.
3. The process of claim 1 wherein the concentration of H.sub.2 O.sub.2 is
about 1 wt. % or less.
4. The process of claim 1 wherein said coating is selected from the group
consisting of organically modified cellulose, polyvinyl alcohol, and
dibutyl phthalate.
5. The process of claim 1 wherein said lens and said neutralizer are placed
into said H.sub.2 O.sub.2 solution within 5 minutes of each other.
6. The process of claim 1 wherein said lens and said neutralizer are placed
into said H.sub.2 O.sub.2 solution within 1 minute of each other or
simultaneously.
7. The process of claim 1 wherein the said neutralizer also contains up to
about 10 wt. % of a mixture of an acid and a base which react in solution
to form CO.sub.2 gas.
8. The process of claim 1 wherein the concentration of H.sub.2 O.sub.2 in
said buffered, saline lens storage solution is less than about 40 ppm.
9. The process of claim 1 wherein said neutralizer also contains up to
about 1 wt. % of a chelating agent and up to about 5 wt. % of a
preservative.
10. The process of claim 1 wherein said one or more H.sub.2 O.sub.2
-neutralizing compounds comprises sodium thiosulfate or sodium sulfite.
11. The process of claim 1 wherein the lens is not removed from said
aqueous solution until after the solution has been transformed into a
buffered, saline lens storage solution.
12. The process of claim 11 wherein the lens and the tablet are sealed
together into a closed container containing said disinfecting solution,
and the container is not opened again until after said disinfecting
solution has been transformed into a buffered, saline lens storage
solution.
13. A process for disinfecting a contact lens, comprising
(A) immersing the lens in a predetermined volume of an aqueous disinfecting
solution consisting essentially of H.sub.2 O.sub.2 at a concentration of
about 3 wt. % or less which is effective to disinfect the lens in a
disinfection period of less than about 6 hours, and
(B) decomposing the H.sub.2 O.sub.2 in said disinfecting solution by adding
to said solution, before said disinfection period has elapsed, a
neutralizer in the form of a tablet or a plurality of particles and
comprising
one or more H.sub.2 O.sub.2 -neutralizing compounds which react with
H.sub.2 O.sub.2 to form H.sub.2 O and reaction products which are
non-injurious to the eye, in an amount of said one or more compounds
effective to react with all the H.sub.2 O.sub.2 in said solution;
one or more water-soluble agents in an amount thereof effective to provide
that an aqueous solution having said predetermined volume and containing
said reaction products and said water-soluble agents has a pH of 6.5 to
8.5 and a tonicity of 200 to 450 milliosmol per kg of solution, and
a coating encasing said tablet or each of said particles which coating
dissolves gradually in said H.sub.2 O.sub.2 solution, so as to release
said one or more H.sub.2 O.sub.2 -neutralizing compounds and water-soluble
agents only after said disinfection period has elapsed,
whereby said released neutralizing compounds and agents transform said
H.sub.2 O.sub.2 solution in situ into a buffered, saline lens storage
solution.
14. The process of claim 13 wherein said water-soluble agents comprise a
mixture of sodium borate and boric acid.
15. The process of claim 13 wherein the amount of said water-soluble agents
is effective to provide that said resulting solution has a pH of about 7.0
to about 7.9.
16. The process of claim 13 wherein said coating is selected from the group
consisting of organically modified cellulose, polyvinyl alcohol, and
dibutyl phthalate.
17. The process of claim 13 wherein said neutralizer also contains up to
about 1 wt. % of a chelating agent and up to about 5 wt. % of a
preservative.
18. The process of claim 13 wherein the neutralizer also contains up to 10
wt. % of a mixture of an acid and a base which react in solution to form
CO.sub.2 gas.
19. The process of claim 13 wherein said lens and said neutralizer are
placed into said H.sub.2 O.sub.2 solution within 5 minutes of each other.
20. The process of claim 13 wherein said lens and said neutralizer are
placed into said H.sub.2 O.sub.2 solution within 1 minute of each other or
simultaneously.
21. A kit for disinfecting a contact lens in a predetermined volume of an
aqueous disinfecting solution of H.sub.2 O.sub.2 having a predetermined
concentration, and for neutralizing the H.sub.2 O.sub.2 in said solution
after a disinfection period which is a function of said predetermined
concentration and for transforming the solution in situ into a buffered
isotonic lens storage solution; said kit comprising means for washing the
lens, and a neutralizer in the form of a tablet or a plurality of
particles, wherein said neutralizer comprises
one or more H.sub.2 O.sub.2 -neutralizing compounds which react with
H.sub.2 O.sub.2 to form H.sub.2 O and reaction products which are
non-injurious to the eye, in an amount of said one or more compounds
effective to react with all the H.sub.2 O.sub.2 in said disinfecting
solution and thereby to form an aqueous solution containing dissolved
therein said reaction products and having a pH of 6.5 to 8.5 and a
tonicity of 200 to 400 milliosmol per kg of solution, and
a coating encasing said tablet or each of said particles, which coating is
characterized in that when said coated tablet or particles is placed in
said H.sub.2 O.sub.2 solution before the end of said disinfection period,
said coating gradually dissolves in the H.sub.2 O.sub.2 solution, and
releases said one or more neutralizing compounds only after said
disinfection period has elapsed.
22. The kit according to claim 21, which further comprises up to 10 wt. %
of an acid and a base which react in solution to form CO.sub.2 gas and
water-soluble products which are non-injurious to the eye.
23. The kit of claim 22 wherein said acid is selected from the group
consisting of citric, tartaric, and malic acids, and said base is sodium
bicarbonate.
24. The kit of claim 21 wherein said means for washing the lens comprises a
container open at its top for receiving said predetermined volume of said
H.sub.2 O.sub.2 solution and a lens case agitator;
a lidlike member removably mounted on the top end of the container and open
at both ends and having a transverse partition intermediate its ends;
said partition having an aperture extending therethrough;
a lens case agitator pivotally mounted in said aperture in the partition
and extending into said container and having depending lens case
supporting means and an upper end extending above the partition and having
a spur gear thereon;
a knoblike member pivotally received in the upper end of the lidlike member
and having finger grasp means for rotating the same and internal gear
teeth therein;
planetary gear means pivotally mounted on said transverse top portion of
the lidlike member and interposed between said spur gear on the agitator
and said internal gear teeth in the knoblike member for imparting rotation
to said agitator member whereby a lens carried in said lens case is washed
in the liquid in the container; and
lens case means, attached to said lens case supporting means, for holding a
lens in communication with said solution.
25. The kit of claim 21 wherein said coating is characterized in that when
the neutralizer is placed in said H.sub.2 O.sub.2 solution up to 5 minutes
after the beginning of said disinfection period, said coating dissolves
only after said disinfection period has elapsed.
26. The kit of claim 21 further comprising a bottle of an aqueous solution
of H.sub.2 O.sub.2 having said predetermined concentration.
27. A kit for disinfecting a contact lens in a predetermined volume of an
aqueous disinfecting solution of H.sub.2 O.sub.2 having a predetermined
concentration, and for neutralizing the H.sub.2 O.sub.2 in said solution
after a disinfection period which is a function of said predetermined
concentration and for transforming the solution in situ into a buffered
isotonic lens storage solution; said kit comprising means for washing the
lens, and a neutralizer in the form of a tablet or a plurality of
particles, wherein said neutralizer comprises
one or more H.sub.2 O.sub.2 -neutralizing compounds which react with
H.sub.2 O.sub.2 to form H.sub.2 O and reaction products which are
non-injurious to the eye, in an amount of said one or more compounds
effective to react with all the H.sub.2 O.sub.2 in said disinfecting
solution,
one or more water-soluble agents in an amount thereof effective to provide
that an aqueous solution having said predetermined volume and containing
dissolved therein said reaction products and said water-soluble agents has
a pH of 6.5 to 8.5 and a tonicity of 200 to 400 milliosmol per kg of
solution, and
a coating encasing said tablet or each of said particles, which coating is
characterized in that when said coated tablet or particles is placed in
said H.sub.2 O.sub.2 solution before the end of said disinfection period,
said coating gradually dissolves in the H.sub.2 O.sub.2 solution, and
releases said one or more neutralizing compounds and water-soluble agents
only after said disinfection period has elapsed.
28. The kit according to claim 27 wherein said one or more water-soluble
agents are selected from the group consisting of boric acid, sodium
borate, and mixtures thereof.
29. The kit of claim 27 further comprising a bottle of an aqueous solution
of H.sub.2 O.sub.2 having said predetermined concentration.
30. A neutralizer suitable for use in a kit for disinfecting a contact lens
in a predetermined volume of an aqueous disinfecting solution of H.sub.2
O.sub.2 having a predetermined concentration, and for neutralizing the
H.sub.2 O.sub.2 in said solution after a disinfection period which is a
function of said predetermined concentration and for transforming the
solution in situ into a buffered isotonic lens storage solution, which kit
comprises means for washing the lens, and a neutralizer; which neutralizer
is in the form of a tablet or a plurality of particles and comprises
one or more H.sub.2 O.sub.2 -neutralizing compounds which react with
H.sub.2 O.sub.2 to form H.sub.2 O and reaction products which are
non-injurious to the eye, in an amount of said one or more compounds
effective to react with all the H.sub.2 O.sub.2 in said disinfecting
solution and thereby to form an aqueous solution containing dissolved
therein said reaction products and having a pH of 6.5 to 8.5 and a
tonicity of 200 to 400 milliosmol per kg of solution, and
a coating encasing said tablet or each of said particles which coating is
characterized in that when said coated tablet or particles is placed in
said H.sub.2 O.sub.2 solution before the end of said disinfection period,
said coating gradually dissolves in the H.sub.2 O.sub.2 solution, and
releases said one or more neutralizing compounds only after said
disinfection period has elapsed.
31. The neutralizer according to claim 30, which further comprises up to 10
wt. % of an acid and a base which react in solution to form CO.sub.2 gas
and water-soluble products which are non-injurious to the eye.
32. The neutralizer of claim 31 wherein said acid is selected from the
group consisting of citric, tartaric, and malic acids, and said base is
sodium bicarbonate.
33. The neutralizer of claim 30 wherein said coating is characterized in
that when the neutralizer is placed in said H.sub.2 O.sub.2 solution up to
5 minutes after the beginning of said disinfection period, said coating
dissolves only after said disinfection period has elapsed.
34. A neutralizer suitable for use in a kit for disinfecting a contact lens
in a predetermined volume of an aqueous disinfecting solution of H.sub.2
O.sub.2 having a predetermined concentration, and for neutralizing the
H.sub.2 O.sub.2 in said solution after a disinfection period which is a
function of said predetermined concentration and for transforming the
solution in situ into a buffered isotonic lens storage solution, which kit
comprises means for washing the lens, and a neutralizer; which neutralizer
is in the form of a tablet or a plurality of particles and comprises
one or more H.sub.2 O.sub.2 -neutralizing compounds which react with
H.sub.2 O.sub.2 to form H.sub.2 O and reaction products which are
non-injurious to the eye, in an amount of said one or more compounds
effective to react with all the H.sub.2 O.sub.2 in said disinfecting
solution,
one or more water-soluble agents in an amount thereof effective to provide
that an aqueous solution having said predetermined volume and containing
dissolved therein said reaction products and said water-soluble agents has
a pH of 6.5 to 8.5 and a tonicity of 200 to 400 milliosmol per kg of
solution, and
a coating encasing said tablet or each of said particles which coating is
characterized in that when said coated tablet or particles is placed in
said H.sub.2 O.sub.2 solution before the end of said disinfection period,
said coating gradually dissolves in the H.sub.2 O.sub.2 solution, and
releases said one or more neutralizing compounds and water-soluble agents
only after said disinfection period has elapsed.
35. The neutralizer according to claim 34 wherein said one or more
water-soluble agents are selected from the group consisting of boric acid
sodium borate, and mixtures thereof. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This application relates to the disinfection of contact lenses, and more
particularly to disinfection by water-borne chemical agents without the
application of heat.
Contact lenses accumulate dirt, proteinaceous matter, and microorganisms,
all of which can adversely affect the health of the eye if allowed to
accumulate on the lens. Therefore, the lenses must be cleaned and
disinfected regularly and preferably daily.
It is generally known that hydrogen peroxide, in aqueous solution at a
concentration of 3 wt. %, can be used to disinfect contact lenses and
simultaneously remove unwanted dirt and proteinaceous matter. However, the
hydrogen peroxide (hereafter, H.sub.2 O.sub.2) will irritate the eye if
even a small residual amount remains on the lens when it is re-inserted
into the eye. This problem is especially notable with soft contact lenses,
which are made from a water-permeable polymer into which the H.sub.2
O.sub.2 can penetrate. Removing the H.sub.2 O.sub.2 from such material is
particularly difficult, and has required extensive washing and soaking
with saline solution. Thus, it is desirable to be able to employ H.sub.2
O.sub.2 in disinfecting contact lenses, while avoiding the irritancy of
residual H.sub.2 O.sub.2.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 3,829,329 discloses immersing soft contact lenses in a normal
saline (NaCl) aqueous solution of 3% H.sub.2 O.sub.2, to shrink the
lenses. The lenses were then boiled for 2 hours each in distilled water
and normal saline solution. Adopting such a severe boiling regimen for the
daily treatment of soft contact lenses would be inconvenient to the user
and could cause the lenses to deteriorate.
U.S. Pat. No. 3,908,680 discloses a treatment regimen for plastic articles
such as contact lenses, which employs two boiling, aqueous baths
containing a peroxy compound such as H.sub.2 O.sub.2, followed by
cleansing with a nonionic detergent and rinsing with distilled water. This
sequence, besides being overly cumbersome for daily application, is not
sure to remove all residual H.sub.2 O.sub.2.
U.S. Pat. No. 3,912,451 discloses that H.sub.2 O.sub.2 in a solution used
to sterilize soft contact lenses can be subsequently neutralized by
contacting the solution with a metallic catalyst which decomposes the
H.sub.2 O.sub.2. This system is not sure to work quickly, as it relies on
contact between the H.sub.2 O.sub.2 and a solid metallic surface. Such a
system also becomes less and less effective as the concentration of
H.sub.2 O.sub.2 declines; unfortunately, the H.sub.2 O.sub.2 concentration
at which this system loses efficiency can still be high enough to risk
irritation to the eye of the user. In addition, this system requires
several manual or mechanical steps to bring the metallic catalyst into
contact with the H.sub.2 O.sub.2 solution. One such mechanical approach is
disclosed in U.S. Pat. No. 4,013,410, in which a mechanical timer rotates
the container holding the solution so as to bring the solution into
contact with a band of catalytic metal.
An article by A. R. Gasset et al., "Hydrogen Peroxide Sterilization of
Hydrophilic Contact Lenses", in. Arch. Ophthalmol, Vol. 93 (June, 1975)
pp. 412-415, discusses sterilizing soft contact lenses in 3% H.sub.2
O.sub.2 solution. A solution of sodium thiosulfate was used to neutralize
the residual H.sub.2 O.sub.2 remaining in the lenses after sterilization.
The authors found that sodium thiosulfate concentrations of 1.5% and 2.0%
were unable to destroy all residual H.sub.2 O.sub.2, while a 2.5% solution
was effective. Adapting this technique to everyday practice still requires
the user to take several steps that are not all performed at the same
time. This risks the omission of the neutralization step, through haste,
carelessness, or forgetfulness, and also risks miscalculation of the
amount and concentration of the sodium thiosulfate solution that is to be
added.
SUMMARY OF THE INVENTION
The present invention provides a convenient, safe, one-step process for
disinfecting a contact lens. The process comprises:
(A) immersing the lens in a predetermined volume of an aqueous solution
consisting essentially of H.sub.2 O.sub.2 at a concentration of about 3
wt. % or less which is effective to disinfect the lens in a disinfection
period of less than about 6 hours, and
(B) decomposing the H.sub.2 O.sub.2 in said solution by adding to said
solution, before said disinfection period has elapsed, a neutralizer
comprising
one or more H.sub.2 O.sub.2 -neutralizing compounds in tablet or
particulate form which react with H.sub.2 O.sub.2 to form H.sub.2 O and
reaction products which are non-injurious to the eye, in an amount of said
compounds effective to react with all the H.sub.2 O.sub.2 in said
solution, and thereby to form an aqueous solution containing said reaction
products and having a pH of 6.5 to 8.5 and a tonicity of 200 to 450
milliosmol per kg of solution, and
a coating encasing said tablet or particles which coating dissolves
gradually in said H.sub.2 O.sub.2 solution so as to release said one or
more H.sub.2 O.sub.2 -neutralizing compounds and water-soluble agents,
only after said disinfection period has elapsed,
whereby said released compounds transform said H.sub.2 O.sub.2 solution in
situ into a buffered lens storage solution.
This process is particularly useful when the lens and the tablet are placed
in the H.sub.2 O.sub.2 solution 5 minutes or less apart, and more
preferably within 1 minute or less or simultaneously.
The invention also comprises the coated neutralizer, and kits which include
such a neutralizer.
DETAILED DESCRIPTION OF THE INVENTION
The present invention effectively disinfects hard and soft contact lenses,
especially soft lenses, i.e. lenses made of a hydrophilic polymer such as
poly(hydroxyethylmethacrylate). Other such materials are well known to
those skilled in this art. The invention can be carried out in an
apparatus which holds the lenses immersed in an aqueous solution while
permitting the solution to contact all surfaces of both lenses. One such
device is known as the "Hydra-Mat II", described in U.S. Pat. No.
3,623,492, the disclosure of which is hereby incorporated herein by
reference. The present invention will be described with reference to that
device. It includes two perforated baskets for holding a pair of contact
lenses inside a container for a cleaning solution. The baskets are
connected through gears to a knob on the cap of the container; twisting
the knob spins the baskets in the cleaning solution.
The lens to be disinfected by the present invention is first removed from
the eye and then cleaned, preferably by gentle rubbing between the fingers
with a commercial lens cleaning solution for 15-20 seconds or by other
appropriate methods for cleaning. This step, while not an essential part
of the invention, helps loosen soil from the lens surface. The loosened
soil and the cleaning solution are then rinsed off of the lens with saline
solution or tap water, or can be washed off by placing the lens into the
Hydra-Mat II baskets, adding saline solution to the container, and
agitating the baskets by turning the top knob.
To disinfect the lens, it is immersed in an aqueous solution of H.sub.2
O.sub.2. While H.sub.2 O.sub.2 concentrations of 3 wt. % up to 10 wt. %
are effective, the invention can also surprisingly be carried out quite
effectively with H.sub.2 O.sub.2 concentrations of less than about 3 wt.
%, e.g. as low as 1 wt. %, preferably as low as 0.25 wt. %, and even as
low as 0.1 wt. %. The lens can be immersed in the H.sub.2 O.sub.2 solution
by placing it in one lens-holding basket of the Hydra-Mat II device, and
filling enough of the H.sub.2 O.sub.2 solution into the container (after
removing any other washing solutions) so that closing the cap over the
container submerges the lens in the solution.
The low concentration of H.sub.2 O.sub.2 that can be used in this process
is noteworthy because the lens can be effectively disinfected in a
reasonably short time. The low concentration also provides other
advantages. One advantage in particular is that there is a reduced risk of
harm to the eye from residual peroxide remaining in the lens. Another
advantage is that lower peroxide concentrations cause little or no harm to
the lens itself through chemical degradation of the polymeric structure.
There should be a sufficient concentration of H.sub.2 O.sub.2 that the
lens is disinfected in a time up to about 6 hours; this corresponds to an
H.sub.2 O.sub.2 concentration of at least about 0.25 wt. %.
The concentration of H.sub.2 O.sub.2 determines the length of time ("the
disinfection period") for which the lens should be kept immersed in the
H.sub.2 O.sub.2 for disinfection. At H.sub.2 O.sub.2 concentrations of
0.25 wt. %, the lens should be immersed in the H.sub.2 O.sub.2 solution
for about 6 hours to be sure of satisfactorily complete disinfection,
whereas at 0.5 wt. % H.sub.2 O.sub.2, the immersion time should be about 3
hours; and at 1.0 wt. % H.sub.2 O.sub.2, immersion should be for about 2
hours, whereas a concentration of 3.0 wt. % H.sub.2 O.sub.2 calls for
immersion lasting about 5 minutes. One skilled in this art can readily
determine the appropriate times for other initial concentrations of
H.sub.2 O.sub.2.
Another distinct and unobvious advantage of this process is the means by
which the peroxide is removed from the lens. Specifically, a neutralizer
is provided which is used to neutralize the H.sub.2 O.sub.2 after a
predetermined period of time and to transform the H.sub.2 O.sub.2 solution
into an essentially H.sub.2 O.sub.2 -free, buffered saline solution in
which the lens can be safely stored. The lens can be removed immediately
from the neutralized solution and reinserted into the eye, or it can be
stored in the solution for a lengthy period of time, such as overnight.
In the broadest aspect of this invention, the neutralizer is placed into
the H.sub.2 O.sub.2 solution in which the lens is immersed at any time
before the lens is completely disinfected, and the component(s) of the
neutralizer are released into the H.sub.2 O.sub.2 solution only after the
lens has been in the solution long enough to be disinfected. In the
preferred embodiment of the invention, the lens and the neutralizer are
placed into the H.sub.2 O.sub.2 solution at about the same time, that is,
within 5 minutes of each other, preferably within one minute, and more
preferably essentially simultaneously.
The present invention, in its preferred embodiment in which the neutralizer
and lens are placed into the H.sub.2 O.sub.2 solution at essentially the
same time, is particularly advantageous because it lets the lens wearer
perform all the necessary steps at one time. By placing the neutralizer
and lens into the H.sub.2 O.sub.2 together, the user does not need to
return later to remove residual H.sub.2 O.sub.2 from the lens or to
discard the H.sub.2 O.sub.2 solution. Thus, there is no chance of the user
forgetting to carry out such a subsequent step. In addition, once the
lens, neutralizer, and H.sub.2 O.sub.2 are sealed into a container (such
as the Hydra-Mat II) the user does not need to break sterility, i.e. he or
she does not need to invade the sterilized environment of the lens-H.sub.2
O.sub.2 system, and risk re-infecting the lens, to get rid of the H.sub.2
O.sub.2 solution. The neutralizer destroys the H.sub.2 O.sub.2 for the
user, inside the sterilized environment.
The neutralizer includes one or more H.sub.2 O.sub.2 -neutralizing
compounds that can react with H.sub.2 O.sub.2 to form H.sub.2 O and
byproducts that do not injure the lens or the eye of the lens wearer. The
most preferred neutralizer is sodium thiosulfate. Neutralizers that can be
used include thiourea (H.sub.2 NC(S)NH.sub.2), sodium sulfite (Na.sub.2
SO.sub.3), thioglycerol (HOCH.sub.2 CH(OH)CH.sub.2 SH), sodium formate
(HCOONa), ascorbic acid
##STR1##
isoascorbic acid (erythorbic acid)
##STR2##
oxalic acid (--COOH).sub.2), glyoxylic acid (OCHCOOH), and tartaric acid
(--CHOHCOOH).sub.2) Other neutralizers can work catalytically, such as
platinum or other metals belonging to Period 4, 5, or 6 of the Periodic
Table, or peroxidase/ catalase enzyme, but these are expensive, and do not
react to form a buffered lens storage solution.
The amount of the H.sub.2 O.sub.2 -neutralizing compound or compounds to
include in the neutralizer should be sufficient to react with all the
H.sub.2 O.sub.2 contained in the solution in which the lens is immersed.
If sodium thiosulfate is employed, there should be at least a
stoichiometric amount based on the amount of H.sub.2 O.sub.2, that is, 1
mole of Na.sub.2 S.sub.2 O.sub.3 per mole of H.sub.2 O.sub.2. A small
excess is acceptable but higher amounts of the compound(s) are not
necessary. The final concentration of H.sub.2 O.sub.2 in the solution
after all the H.sub.2 O.sub.2 -neutralizing compound is dissolved and
reaction has occurred should be less than 40 ppm, and is preferably less
than 10 ppm. The neutralization is usually complete within 2 hours.
The neutralizer can also optionally contain water-soluble buffering agents
to provide that when the neutralizer dissolves, and the H.sub.2 O.sub.2 is
completely neutralized, the resulting solution of buffering agents,
neutralization reaction products, and excess neutralizer (if any) is a
stable, buffered solution in which the lens can be safely stored.
Whether buffering agents are added or not, the resultant solution should
have a pH value of 6.5 to 8.5, and more preferably 7.0 to 7.9. The
tonicity of the solution should be such that the osmotic pressure of the
solution will permit the immersed lens to retain its normal shape, and
thus should be about 200 to about 450 milliosmolar (mOs) per kg of
solution. Those familiar with this art will recognize that this range
corresponds to a range of about 0.6-1.4% NaCl equivalents. The solution
should be isotonic with eye fluids, or up to about 1.4% hypertonic.
Satisfactory buffering agents include a mixture of sodium borate and boric
acid in amounts which permit the above pH and tonicity to be attained.
Typical amounts of a sodium borate/boric acid buffer are about 0.1 to
about 1.0 wt. % of the eventual solution. Other buffering systems that can
be used include systems based on monobasic and dibasic sodium phosphate;
sodium citrate; or sodium carbonate. It will be recognized that the amount
of buffering agent is a function of the initial liquid volume of the
H.sub.2 O.sub.2 solution, and of the amount of neutralizing agent (because
its reaction products, e.g. Na.sup.+ and SO.sub.3 -.sup.2 ions, will also
influence the pH and tonicity). The amount of buffering agent can readily
be determined by those skilled in this art, with reference to the
parameters mentioned herein.
It should be recognized, though, that frequently the reaction between the
H.sub.2 O.sub.2 and the H.sub.2 O.sub.2 -neutralizing compound will itself
form a solution whose pH and tonicity are within the indicated limits,
thereby making additional buffering agents unnecessary.
The neutralizer optionally, and preferably, also contains a small amount
(less than 1 wt. %) of a chelating agent such as EDTA to complex trace
metals that may be present in the system. This additive helps retain the
stability of the other agents in the solution, and helps any preservative
that may be present retain its activity. Examples of suitable
preservatives for inclusion in the tablet include potassium sorbate,
sorbic acid, thimerosal, chlorhexidine, methyl and propyl parabens,
chlorbutanol, benzalkonium chloride, and phenyl mercuric acetate and
nitrate. These preservatives protect the neutralizer but more importantly
act in solution, following dissolution of the tablet, to protect the lens.
The preservative can comprise up to about 5.0 wt. % of the neutralizer.
The neutralizer can also include an acid and a base which form an
effervescent couple that react in solution to generate a stream of
CO.sub.2 bubbles when the components dissolve. The base should preferably
be sodium bicarbonate, and the acid is preferably a weak organic acid such
as tartaric, citric or malic acid. The acid and base should be present in
amounts which are approximately equimolar, and the acid and base together
can comprise up to about 10 wt. % of the neutralizer. The CO.sub.2 bubbles
formed by reaction between the acid and base can aid the dispersion of any
other components in the H.sub.2 O.sub.2 solution, and can thereby decrease
the time needed to neutralize the solution. Alternatively, the user can
agitate the container of solution (as by twisting the cap of the Hydra-Mat
II) after the coating around the neutralizer has dissolved, to assist the
dispersion of the components.
The neutralizer (by which we include capsules and the like) has a coating
which provides that the neutralizing and (if any) buffering agents will
come into contact with, and dissolve into, the H.sub.2 O.sub.2 solution
only a predetermined length of time after the neutralizer is placed into
the solution. The coating is made of material which is dissolved or
decomposed gradually by H.sub.2 O.sub.2 ; suitable materials include
organically modified cellulose, such as hydroxypropylmethyl cellulose,
ethyl cellulose, cellulose acetate phthalate, hydroxypropyl cellulose;
polyvinyl alcohol; and dibutyl phthalate. The thickness of the coating can
readily be determined as follows. The length of time (t.sub.c) for which
the coating must keep the other agents from dissolving is readily
determined from the length of the disinfection period (t.sub.d), which as
discussed above is a function of the concentration of the H.sub.2 O.sub.2
solution that is being used. If the lens and the neutralizer are placed
into the H.sub.2 O.sub.2 solution at the same time, then t.sub.c equals
t.sub.d. If the neutralizer is to be added a higher number of minutes
after the lens is placed into the H.sub.2 O.sub.2 solution, then t.sub.c
is less than t.sub.d by that number; if the neutralizer is to be added a
higher number of minutes before the lens is immersed, then t.sub.c exceeds
t.sub.d by that number. One can independently determine the rate at which
a given coating material is dissolved by a solution of H.sub.2 O.sub.2 at
the concentration being used, and by multiplying t.sub.c by the rate of
the H.sub.2 O.sub.2 concentration being used, one can calculate how much
of that coating to apply to a neutralizer for use with an H.sub.2 O.sub.2
solution having that concentration. It is advantageous to make the coating
5 to 15% thicker than the calculated value, to ensure that the lens is
exposed to unneutralized H.sub.2 O.sub.2 for a sufficient disinfection
time and to compensate for any slight loss of H.sub.2 O.sub.2 due to
reaction with the coating material.
The neutralizer can be a coated tablet, which can be made by dry blending
the neutralizing and buffering agents, as well as the optional
preservative and chelating agent, to obtain a uniform mixture, and then
tabletting the blend employing conventional tabletting machinery.
Separately, an amount of the coating material sufficient to form coatings
of the desired thickness is dissolved in a solvent such as ethanol or
acetone, and the solution is sprayed onto the tablets so as to form a
uniform coating. The solvent is then evaporated, leaving the desired
coating.
Alternatively, and preferably, instead of having all desired ingredients in
one coated tablet one can prepare a number of particles each of which has
a coating with the characteristics described above, provided that the
particles provide in the aggregate a sufficient amount of the H.sub.2
O.sub.2 -neutralizing compound(s) and of the other components to achieve
the neutralization and (optional) buffering and effervescing functions
described herein. Each particle can be homogeneous, that is, contains only
one compound, or the particles can be heterogeneous, that is, they may
contain two or more of the desired compounds. For instance, if an
effervescent couple is used, it may be advantageous to put the acid and
the base into separate coated particles. The particles can be formed and
coated in the manner described above for tablets. The particles can be
sold and used conveniently in the form of foil packets, two-piece
capsules, or the like, each of which contains enough of the H.sub.2
O.sub.2 -neutralizing compound(s) and the other desired ingredients to
comprise one "dose". It will be appreciated that any number of particles,
e.g. 2 to 100 or more, can be used. After the user washes the lens and
places it into the H.sub.2 O.sub.2 solution, the user simply opens the
packet, capsule, or other container and dumps all the contents into the
H.sub.2 O.sub.2 solution, instead of dropping a tablet into the solution
in the manner described below.
It will be recognized that all components of the tablet should be
non-irritating to the eye when in solution. Standard tests for determining
non-irritability to the eye are known to those skilled in this field. The
H.sub.2 O.sub.2 solutions can contain up to 0.05 wt. % of a stabilizer,
and if so it should not react with or discolor the lens. A satisfactory
stabilizer is a mixture of sodium stannate and sodium pyrophosphate, in a
ratio of about 60:40 to 40:60 by weight.
The invention is described in the following Examples:
EXAMPLES 1-6
Mixtures of materials were compounded into preparations having the
composition given below. Each preparation was added to 7 ml of an aqueous
solution of 0.5 wt. % H.sub.2 O.sub.2. The time required for
neutralization, and the pH and tonicity of the final solution, are also
given. In each case, the final concentration of H.sub.2 O.sub.2 was less
than 40 ppm. Examples 2 and 6 were effervescent, i.e. on dissolution
bubbles of CO.sub.2 formed which dispersed the other components throughout
the solution.
______________________________________
Example No.:
Ingredients
(mg): 1 2 3 4 5 6
______________________________________
Sodium thio-
190 180 180 180 180 190
sulfate
Potassium
10 -- -- 10 10 10
sorbate
Disodium 10 2 -- 2 2 10
EDTA
Boric acid
42 -- 7.5 7.5 15 42
Sodium bicar-
-- 12 5 5 10 12
bonate
Citric acid
-- 8 -- -- -- 8
Sodium phos-
-- -- 7 7 -- --
phate (mono-
basic)
Sodium phos-
-- -- 10 10 -- --
phate (diba-
sic)
Time (hr) to
1-2 4 4 4 3 1-2
complete
neutralization
pH of neu-
7.9 7.3 7.2 7.0 7.9 7.9
tralized solu-
tion
Tonicity 410. 275. 303. 319. 316. 410.
(mOs/kg) of
neutralized
solution
______________________________________
Another embodiment of this invention comprises a kit for disinfecting
lenses with an H.sub.2 O.sub.2 solution and for neutralizing the H.sub.2
O.sub.2 solution. The kit comprises means for washing the lens, and a
tablet or particulate neutralizer of the type described herein. The lens
washer means is advantageously of the type having
a container open at its top for receiving lens washing fluid and a lens
case agitator;
a lidlike member removably mounted on the top end of the container and open
at both ends and having a transverse partition intermediate its ends; said
partition having an aperture extending therethrough;
a lens case agitator pivotally mounted in said aperture in the partition
and extending into said container and having depending lens case
supporting means and an upper end extending above the partition and having
a spur gear thereon;
a knoblike member pivotally received in the upper end of the lidlike member
and having finger grasp means for rotating the same and internal gear
teeth therein;
planetary gear means pivotally mounted on said transverse top portion of
the lidlike member and interposed between said spur gear on the agitator
and said internal gear teeth in the knoblike member for imparting rotation
to said agitator member whereby a lens carried in said lens case is washed
in the liquid in the container;
and a lens case, attached to the lens case agitator, for holding a lens in
communication with liquid in said container (a small concave bowl, having
perforations to let liquid pass through but not letting the lens fall
therethrough, and having a detachable lid, is satisfactory);
or equivalents of such a device.
The kit is employed in the manner described herein, to clean and disinfect
a contact lens. The composition of the tablet or the quantity of
particulate neutralizer is predetermined to be used with a specified
volume of aqueous H.sub.2 O.sub.2 solution having a specified
concentration, and instructions are provided with the kit to inform the
user of the strength and volume of the H.sub.2 O.sub.2 solution to use.
More advantageously, the kit includes a bottle of an aqueous solution of
H.sub.2 O.sub.2, whose concentration is predetermined (0.25-3 wt. %) in
conjunction with the composition of the tablet. In this embodiment, the
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