Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Utilizing plasma – electric – electromagnetic – particulate – or...
Patent
1987-09-30
1989-10-17
Lowe, James
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Utilizing plasma, electric, electromagnetic, particulate, or...
264 11, 264 26, B29D 1100
Patent
active
048745626
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a soft contact lens comprising a poly(vinyl alcohol) (PVA) of a high mechanical strength, high water content, excellent transparency, and high oxygen permeability, and a method of manufacturing the same.
BACKGROUND OF THE INVENTION
There are two kinds of contact lenses, soft and hard. The material for the hard contact lens(HCL) is a synthetic resin with network structure containing poly(methyl methacrylate)(PMMA) as a main component and a crosslinking agent. This polymer is widely used in clinical field for HCL because the transparency, the molding processability, the biostability, and the durability are excellent, but this HCL is not suitable for extended wear because the oxygen permeability is not high enough for the respiratory metabolism of the eyeballs and the hard nature of the material gives a feeling of foreign body to the patient.
Materials widely used for the soft contact lens(SCL) in clinical field include a silicone elastomer and a copolymer of butyl acrylate(BA) and butyl methacrylate(BMA) as hydrophobic ones and poly(hydroxyethyl methacrylate)(PHEMA) and a copolymer of methyl methacrylate(MMA) and vinyl pyrrolidone(VP) as hydrophobic ones. These materials are superior to the HCL in oxygen permeability. However, the hydrophobic materials have disadvantages such as poor wear feeling caused by lower water wettability, remarkable adsorption of lipids, and surface damage due to high electrostatic charging, while the hydrophilic ones are very high in production cost, strongly adsorbed with proteins, and very low in mechanical strength, although they give excellent wear feeling and minimum damage to cornea.
The PVA hydrogels have already been proposed as materials for SCL, for instance PVA gels crosslinked with glyoxal (U.S. Pat. No. 3,408,429) and PVA contact lens crosslinked with borates (Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 75111/1983). However, these may stimulate the patient cornea through unreacted compounds remaining in the gel or degradation products with the lapse of time, since these gels are chemically crosslinked with glyoxal and borates. On the other hand, a PVA contact lens is proposed which is prepared through annealing (Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 214128/1982, but this is not sufficient in water content and mechanical strength and needs a complicated and long fabrication process.
As a result of the present inventors' intensive study for solving the defects of the conventional PVA hydrogel SCL, and for developing a simple and unexpensive method of production of SCL which is improved in mechanical strength and has a high water content, an SCL of a high strength, water content and oxygen permeability fabricated in a simple and unexpensive method can be obtained by dissolving PVA in a mixed solvent consisting of water and an organic solvent, followed by crystallizing the PVA between its molecular chains at a temperature of not more than ordinary temperature.
DISCLOSURE OF THE INVENTION
The present invention relates to a soft contact lens of PVA which has a tensile strength of not less than 10 kg/cm.sup.2, a water content ranging from 40 to 95 % by weight, a visible light transparency of not less than 90 %, and an oxygen permeability of not less than than 30.times.10.sup.-11 cm.sup.3 (STP).cm/cm.sup.2.sec.mmHg. The PVA soft contact lens having an excellent strength, water content and oxygen permeability can be obtained by dissolving PVA in a mixed solvent consisting of water and an organic solvent, followed by pouring the PVA solution into a convex and concave mold substantially corresponding to the contact lens shape and subsequent cyrstallization of PVA at a temperature of not more than ordinary temperature.
The PVA soft contact lens of the invention is excellent in transparency and oxygen permeability as well as in mechanical strength and water content. The reason for formation of such a PVA soft contact lens with a high water content and strength is seemed in the following. The s
REFERENCES:
patent: 4559186 (1985-12-01), Lee
Hyon Suong-Hyu
Ikada Yoshito
Biomaterials Universe Inc.
Lowe James
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