Agent for contact lenses

Details Agent for contact lenses Agent for contact lenses

1999-03-23

2001-01-23

Warden, Jill (Department: 1743)

Colloid systems and wetting agents; subcombinations thereof; pro

Continuous liquid or supercritical phase: colloid systems;...

Aqueous continuous liquid phase and discontinuous phase...

C516S072000, C516S110000, C510S112000, C510S383000, C510S489000, C424S078040, C514S496000

Reexamination Certificate

active

06177480

ABSTRACT:

The present invention relates to an agent for contact lenses. Particularly, it relates to an agent for contact lenses, which is useful for cleaning, preserving, rinsing, stabilizing, disinfecting or fitting contact lenses.
Heretofore, as one type of an agent for contact lenses to be used for treatment such as cleaning, rinsing, preserving or disinfecting contact lenses, an agent of high viscosity type is known which has a viscosity of a solution type agent for contact lenses increased from the viewpoint of handling efficiency or efficiency for an operation of treatment of contact lenses with it. For example, a high viscosity type cleaning agent for contact lenses, is known wherein the viscosity of a cleaning solution is increased by means of a common thickener such as carboxymethyl cellulose.
However, if such a high viscosity type cleaning agent is employed for cleaning a contact lens, such a cleaning agent is likely to remain on the contact lens surface, and it has been difficult to adequately wash it off even if rinsing of the contact lens is repeated. Further, in a case where an organic polymer thickener is used to increase the viscosity of the solution, such a thickener itself becomes a nutrient for bacteria, and accordingly there has been a problem that bacteria are likely to propagate in the agent for contact lenses, such as a cleaning agent.
Therefore, various preservatives are incorporated to most of high viscosity type liquid agents to be used for such care of contact lenses, in order to control or prevent the propagation of bacteria due to the presence of a thickener. However, such preservatives are likely to be absorbed by contact lenses, and if a contact lens having a preservative absorbed, is put on the eye, the user of the contact lens may suffer from a corneal trouble such as an allergy.
Under these circumstances, the present invention has been made, and it is an object of the present invention to provide an agent for contact lenses, whereby high viscosity and rinsing efficiency can both be satisfied, while cleaning power is improved, and the surface wettability of contact lenses can be improved, and the anti-lipid staining property can also be improved.
In order to solve the above mentioned problems, the present invention provides an agent for contact lenses, which comprises an aqueous medium and synthetic smectites particulates consisting essentially of primary particles having a particle size of at most 200 nm, dispersed in the aqueous medium.
Thus, with the agent for contact lenses according to the present invention, the prescribed synthetic smectite particulates are dispersed in the aqueous medium, whereby a proper high viscosity can be imparted to the aqueous medium (the liquid agent) due to the thixotropic properties of such particulates. On the other hand, when applied to a contact lens, excellent rinsing efficiency can be obtained as compared with one employing a usual thickener such as carboxymethyl cellulose. In addition, such prescribed synthetic smectite particulates are adsorbed on the lens surface to form a coating film, whereby the hydrophilic property (water wettability) of the contact lens will be effectively improved, and the particulates themselves will adsorb a stain of lipids, proteins, etc., whereby the cleaning power will be improved. Further, deposition or adsorption of a stain to the contact lens will be thereby controlled, and improvement of the anti-lipid staining property can effectively be accomplished.
In a preferred embodiment of the agent for contact lenses according to such present invention, the synthetic smectite particulates are dispersed and incorporated in the aqueous medium in a proportion of from 0.001 to 15 wt %, and the pH of the agent for contact lenses thereby obtained, is adjusted to be within a range of from 8.0 to 11.0, particularly preferably within a range of from 8.5 to 10.5.
In the present invention, as the synthetic smectite particulates, particulates of synthetic sodium-magnesium silicate are advantageously used.
In another preferred embodiment of the agent for contact lenses according to the present invention, at least one of a surfactant, a polyhydric alcohol and a peptizer is further incorporated. As the surfactant, an anionic surfactant may be advantageously used, and as the polyhydric alcohol, propylene glycol may advantageously be used. Propylene glycol serves also as an isotonic agent.
The agent for contact lenses according to the present invention may be prepared in the form of a usual liquid formulation or may advantageously be prepared in the form of a gel formulation having no substantial fluidity due to the high viscosity. In such a gel formulation, it is possible to prevent proliferation of bacteria and thereby to make it substantially unnecessary to use a preservative. Namely, the synthetic smectite particulates are inorganic material and will not themselves serve as a nutrient source for e.g. bacteria, whereby bacteria will scarcely propagate. Accordingly, when the agent for contact lenses is made into a gel type, it is possible to effectively control propagation or proliferation of bacteria and therefore to make it unnecessary to incorporate a disinfectant or a preservative. Accordingly, by using no disinfectant or preservative, it is possible to avoid an allergy or a corneal trouble which may otherwise be caused by such a disinfectant or a preservative.
The synthetic smectite particulates to be dispersed in an aqueous medium to prepare the agent for contact lenses according to the present invention, are usually particulates having a fine flat plate or disk shape, formed as separated from each layer of a crystal structure in the layered structure of a smectite type synthetic clay mineral. As is well known, in a state where they are dispersed in an aqueous medium, the surfaces of the particulates are negatively charged, and their end portions are positively charged. Accordingly, by an increase of the particle concentration or by an increase of the ion concentration, the repulsion due to the surface negative charges tends to decrease, and a so-called card house structure tends to be formed due to the attraction between such surface negative charges and end portion positive charges, thus exhibiting excellent thickening and thixotropic properties.
As such synthetic smectite particulates, various types have been known. Among them, those having a particle size of at most 200 nm, preferably at most 100 nm, are used in the present invention, in view of the transparency, the thickening effect, the reproducibility of the quality, etc. In addition, if the particle size of the particulates is too large, adsorption on the lens surface tends to be inadequate, and formation of a coating film by such particulates tends to be inadequate, thus leading to a problem that improvement in the water wettability (hydrophilic property) tends to be inadequate. The lower limit in the particle size of such particulates is about 10 nm for the reason of their synthesis, and the plate thickness of such particulates is generally at most 5 nm, usually substantially at most about 1 nm, from the molecular structure.
Further, it is usually preferred that such synthetic smectite particulates have a BET specific surface area of at least 100 m
2
/g, preferably at least 200 m
2
/g, whereby improvement in the water wettability of the contact lens surface can advantageously be realized. The maximum BET specific surface area of such synthetic smectite particulates is usually about 500 m
2
/g.
Various types of synthetic smectite which give such particulates have heretofore been known or commercially available as clay minerals such as synthetic montmorillonite, synthetic hectorite, etc. However, in the present invention, a synthetic sodium-magnesium silicate represented by the following basic structural formula, which is commercially available under a trade name of LAPONITE (available from Nippon Silica Kogyo K.K.), can be used particularly advantageously:
[Si
8
(Mg
5.34
Li
0.66
)O
20
(OH)
4
]Na
0,66
In the present invention, s

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