Note: Descriptions are shown in the official language in which they were submitted.
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BACK~ROUND OF THE INVENTION
The present invention relates to a process for
removing contaminants sticking to the surface o~ contact
lenses.
Contact lenses put presently on the market are
classified into two large groups, i.e. contact lenses of
water-nonabsorptive type and water-absorptive type. In
contact lenses of both types, contaminants such as lipids
and proteins contained in tears stick to the lens surface
during wear of the lenses in the eyes. Accordingly,
removal of contaminants sticking to the lens surface
becomes a serious problem in handling the contact
lenses.
When such contaminants are not sufficiently
removed, the optical property of lenses is impaired, and
also the contaminants not only make a feeling in use of
the lenses bad, but also become a cause bringing about
a serious trouble on ocular tissue. Therefore, it is
necessary to promptly remove contaminants sticking to
the lens surface after taking off the lenses from the
eyes.
It is known that use of a surface active
agent is effective for the removal of contaminants,
particularly lipids, sticXing to the lens surface.
However, a surface active agent has little effect on
- removal of contaminants other than lipids, especially
removal of protein contaminant. Therefore, washing of
contact lenses with only a usual cleaning solution
containing a surface active agent still causes unremoved
contaminants such as proteins to remain on the lens
surface, and when such lenses are left, the contaminants
strongly stick to the lens surface in the form of white
crystal or thin film and remarkably shorten the life of
contact lenses for which the optical property is the
most important.
This tendency is particularly noticeable in
water-absorptive contact lenses made of a polymer of a
hydrophilic monomer as a main component such as
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2-hydroxyethvl methacrylate or N-vinyl pyrrolidone.
That is to say, these water-absorptive contact lenses
are made of water-absorptive materials and, therefore,
the lens itself is easy to become a hotbed of the
propagation of various microorganisms and it is essential
to conduct a boiling sterilization treatment at regular
time intervals in order to prevent the propagation.
However, during the boiling treatment, contaminants
such as proteins on the surface of the lens are denatured
so as to stick more strongly to the lens surface.
Also, in addition to well known ~ater-non-
absorptive contact lenses made of predominantly
polymethyl methacrylate, silicone rubber contact lenses
and contact lenses made of materials containing silicone
component h~ve spread in recent years. These contact
lenses are more easy to adsorb contaminants such as
proteins on the lens surface than the polymethyl
methacrylate contact lenses.
It is common to contact lenses of all kinds
that stic~ing of contaminants onto the lens surface is
a serious problem in handling them, though the degree
of stic~ing of contaminants varies depending on materials
of contact lenses, state of the eye of user, manner of
handling and term of use.
It is an object of the present invention to
provide a process for removing contaminants on the
surface of contact lenses.
A further object of the present invention is
to provide a process for easily removing contaminants,
especially proteins, on the surface of contact lenses
in a short period of time.
These and other objects of the present
invention will become apparent from the description
hereinafter.
SU~ARY OF THE INVENTION
It has now been found that a hypohalogenous
acid salt is very effective for removing contaminants,
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particularly proteins, sticking to the surface of
contact lenses in a short period of time.
In accordance with the present invention,
there is provided a process for removing contaminants
on the surface of contact lenses which comprises
immersing a contact lens in an aqueous solution containing
a hypohalogenous acid salt for an effective period of
time.
DETAILED DESCRIPTION
The term "hypohalogenous acid salt" as used
herein comprehends a water-soluble compound capable of
producing a hypohalogenite ion in water.
Examples of the hypohalogenous acid salt
employed in the present invention are alkali metal or
alkaline earth metal salts of hypohalogenous acids such
as hypochlorous acid, hypobromous acid and hypoiodous
acid, e.g. lithium, sodium, potassium, magnesium or
calcium hypochlorite, hypobromite and hypoiodite. These
hypohalogenous acid salts may be employed alone or in
admixture thereof. AlXali metal hypobromites and
al~aline earth metal hypobromites are preferred among the
above-mentioned salts in point of the effect.
The hypohalogenous acid salt is employed in
the form of aqueous solution in cleaning contact lenses.
The preparation of an aqueous solution of a hypohalo-
genous acid salt may be conducted in various manners,
for instance, hy a process (1~ in which an aqueous
solution of a hypohalogenous acid salt is prepared and
reserved in a suitable vessel, and is used as it is or
after diluting it to a desired concentration with
distilled water or purified water; a process (2) in which
there is prepared a hypohalogenous acid salt in the form
of tablet, powder or granule, and upon treating contact
lenses, it is dissolved in distilled water or purified
water to prepare an aqueous solution of the hypohalo-
genous acid salt having a desired concentration; or a
process (3) in which there is employed a tablet, powder
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or granule of a compound capable of dissolving in water
such as distilled or purified water and producing a
hypohalogenite ion.
The above process (1) is the most convenient,
but an aqueous solution of a hypohalogenous acid salt is
generally unstable and cannot be reserved for a long term.
Therefore, the above processes (2) and (3) are more prac-
tical.
Explaining a typical example of the process
(2), in case that the hypohalogenous acid salt is calcium
salts such as calcium hypochlorite, a tablet, powder or
granule thereof is preferably employed. It is also
possible to employ an alkali metal or alkaline earth
metal hypochlorite such as calcium hypochlorite in com-
bination with an alkali metal or alkaline earth metal
bromide such as potassium bromide to produce hypobromite
ion in an aqueous solution thereof. For instance, a
tablet, powder or granule of calcium hypochlorite is
employed in combination with an aqueous solution, tablet,
powder or granule of potassium bromide.
Examples of the compound used in the above
process (3) are sodium salt of N,N-dichlorotaurine,
N,N'-dichloro-5,5-dimethylhydantoin, N-bromosuccinimide
and N,N-dichloroglycine. These compounds may be employed
in the form of tablet, powder or granule.
The amount of the hypohalogenous acid salt
used and the immersion treatment time of contact lenses
are not critical in the present invention, but in gene-
ral, it is desirable that the concentration of the hypo-
halogenous acid salt in an aqueous solution for immersion
treatment is from about 1 p.p.m. to about 20,000 p.p.m.
and that the immersion treatment time is from about 3
minutes to about 24 hours~
In general, the higher the concentration of a
hypohalogenous acid salt, the shorter the immersion
treatment time. However, in case of treating water-
absorptive contact lenses, it is desirable to employ a
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i. :
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hypohalogenous acid salt in as low concentration as
possible so as to remove contaminants by a mild action of
the hypohalogenite ion, since removal of the hypohalo-
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genous aci~ salt remaining in the lenses after treatment
is made easy and an undesirable influence of the sal~ such
as deterioration of the lens material is avoided. For
instance, water-absorptive contact lenses are immersed in
an aqueous solution containing about~l to about 50 p.p.m.
of a hypohalogenous acid salt for about 3 to 24 hours.
After the completion of the immersion treatment,
the contact lenses are taken out from the aqueous
solution and the remaining hypohalogenous acid salt is
removed from the treated contact lenses. In case of
water-nonabsorptive contact lenses, the hypohalogenous
acid salt remaining on the surface of contact lenses
can be easily removed by sufficiently rinsing the contact
lenses with water such as tap water. In case of water-
absorptive contact lenses, it is difficult to sufficientlyremove the remaining hypohalogenous acid salt in such a
manner as mere rinsing because of the water-absorptivity
of the contact lens material. Therefore, in that case, it
is necessary to subject the immersion-treated contact
lenses to a treatment for making the hypohalogenous acid
salt harmless before rinsing.
The treatment for making the remaining
hypohalogenous acid salt in water-absorptive contact
lenses can be conducted by employing a reducing agent,
e.g. alkali metal or al~aline earth metal salts of
thiosulfuric acid such as sodium thiosulfate, potassium
thiosulfate and calcium thiosulfate, ascorbic acid, and
saccharides such as glucose, mannose, galactose and
lactose. After the completion of the immersion treatment,
the contact lenses are taken out from the immersion
solution and are then immersed in an aqueous solution of
a reducing agent in order to make the remaining
hypohalogenous acid salt harmless. It is of course
possible to after immersing contact lenses in an aqueous
solution containing a hypohalogenous acid salt for a
sufficient period of time, add and dissolve a reducing
agent in the aqueous solution.
When the saccharides such as glucose, mannose,
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galactose and lactose are used as a reducing agent, it
is also possible to make such a reducing agent present
in an aqueous solution of a hypohalogenous acid salt
from the beginning of the immersion treatment for
removing contaminants. The reducing agent is dissolved
in an aqueous solution of a hypohalogenous acid salt
before conducting the immersion treatment of contact
lenses. In that case, it is possible to reduce the
hypohalogenous acid salt, in other words, to make the
treating solution harmless, without impairing the
removal action of the hypohalogenous acid salt on
contaminants sticking to the lens surface, since the
action of the hypohalogenous acid salt on the reducing
agent is slower than the action on the contaminants.
Therefore, this manner is particularly desirable, since
the failure such that contact lenses are immersed in the
treating solution over a prescribed time is prevented.
Witn respect to the amount of the reducing
agent, there is no particular problen~., so far as the
reducing agent is employed in an amount enough to react
with all the hypohalogenous acid salt used.
After making a hypohalogenous acid salt or an
aqueous solution thereof harmless, the contact lenses
are sufficiently rinsed with a 0.9 % by weight
physiological saline water so that the lenses can be
worn on the eyes without any problems.
The process of the present invention is more
particularly described and explained by means of ~he
following Examples.
Example_l
A protein contaminant was stuck to water-
absorptive cuntact lenses (commercial name "MENICON SOFT
made by Toyo Contact Lens Co., Ltd.) as follows:
Five pieces of the contact lenses were
immersed in 100 ml. of an aqueous solution of 1 g. of
lysozyme and 0.9 g. of sodium chloride dissolved in
distilled water for 6 hours, and a~ter taking out from
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the aqueous solution, were rinsed with a slight amount
of physiological saline water. Each lens was placed in
a vessel filled with 1 ml. of a physiological saline
water, and the vessel was sealed with a cap and was
heated to boil for 15 minutes. The contact lenses were
- taken out from the vessels, and the lens surfaces were
cleaned with a puff for contact lens (commercial
name "NE~'CLEAN PUFF" made by Toyo Contact Lens Co., Ltd.)
and a cleaning liquid (commercial name "P~ENI CLEAN"
made by Toyo Contact Lens Co., Ltd.). This cleaning
procedure was repeated ~ times on each lens. It was
confirmed that each lens was completely covered with a
white film of protein, i.e. lysozyme.
The thus contaminated contact lenses were
immersed in 5 ml. of each of ~ p.p.m., lO p.p.m., 20
p.p.n..., 30 p.p.m. and 50 p.p.m. aqueous solutions of
sodium hypochlorite for 16 hours, respectively. The
degree of the removal of contaminant was observed by a
stereoscopic microscope (JrI Tr Type of darX ground
2Q stereoscopic microscope made by OLY~IPUS OPTICAL CO~lPAN~'
LI~IITED).
In case of the treatment with the 30 p.p.m.
and 50 p.p.m. aqueous solutions, the contaminant was
completely remo~ed to restore the transparency of the
lens. In case of the treatment with the 20 p.p.m.
aqueous solution, unremoved contaminant was partly
remained on the lens surface. In case of the treatment
with the 4 p.p.m. and lO p.p.m. aqueous solutions, more
than half of the contaminant remained unremoved.
However, the above aqueous solutions o sodium
hypochlorite in low concentrations, i.e. 4 p.p.m.,
lO p.p.m. and 2n p.p.m., are still effective in practical
use where the treatment is periodically conducted in
order to prevent sticking of contaminants to the
surface of water-absorptive contact lenses.
Example 2
Removal of a protein contaminant with
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hypobromite ion produced by reaction of potassium
bromide and calcium hypochlorite in distilled water was
tested as follows:
Five pieces of water-nonabsorptive contact
lenses (commercial name "~IENICON 2" made by Toyo
Contact Lens Co., Ltd.) contaminated with a protein
were immersed in an aqueous solution of 20 mg. of
potassium bromide dissolved in 10 ml. of distilled water,
and in the a~ueous solution was dissolved 25 mg. of
calcium hypochlorite having 61 % of available chlorine.
After 5 minutes, the lenses were taken out and
sufficiently washed with tap water. The state of the
lens surface was then observed by a stereoscopic
microscope.
In all the contact lenses, the contaminant
was removed to restore the orginal transparency of the
lens.
Example 3
The same water-absorptive contact lens as
used in Example 1 was treated in the same manner as in
Example 2.
After 5 minutes from dissolution of calcium
hypochlorite, five pieces of the lenses were sufficiently
rinsed with a 0.9 % physiological saline water, and the
degree of removal of the contaminant was observed by a
stereoscopic microscope. In all the contact lenses,
the contaminant was removed and the lenses were
transparent.
This process is suitable for use in removing
contaminants on the surface of contact lenses in a
short time in an ophthalmic hospital or an optician.
Example 4
Five pieces of the same wa~er-absorptive
contact lens as used in Example 1, the surface of which
was contaminated with a protein, were immersed in an
aqueous solution of 0.25 mg. of potassium bromide and
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63 mg. of glucose dissolved in 10 ml. of distilled
water, and in the aqueous solution was dissolved 25 mg.
of calcium hypochlorite having 61 % of available
chlorine. After 2 hours, the lenses were taken out and
sufficiently rinsed with a 0.9 % physiological saline
water. The degree of removal of the contaminant was
observed by a stereoscopic microscope.
All the contact lenses so treated had no
contaminant on the surface and had the original
transparency. Also, the presence of hypohalogenite ion
was not observed in the aqueous solution after the
treatment for 2 hours.
Example 5
A treating liquor was prepared by adding 30 mg.
of N,N'-dichloro-5,5-dimethylhydantoin, 25 mg. of potassium
bromide and 50 mg. of sodium carbonate to 10 ml. of
distilled water and thoroughly shaking. Five pieces of the
same water-nonabsorptive contact lens as used in Example
2, the surface of which was contaminated with a protein,
were immersed in the treating liquor for 10 minutes, and
the state of the lens surface was observed in the same
manner as in Example 2. All the contact lenses so treated
had no contaminant on the surface and had the original
transparency.
