Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-06-09
1998-10-13
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
523106, C08L 3306
Patent
active
058213066
DESCRIPTION:
BRIEF SUMMARY
The present invention is related to the field of intraocular lenses and especially to materials based on polyacrylate based polymers to be used in the production of deformable lenses facilitating small incision surgery procedures.
When an ophthalmic surgeon operates on an eye to remove a cataract (s)he replaces the defective natural lens with a small artificial lens. The material most commonly used for the manufacture of such intraocular lenses (IOLs) is the rigid amorphous plastic poly(methylmethacrylate) (PMMA).
In order to remove the natural lens as well as for introducing the IOL an incision into the eye has to be made. The minimum size of an incision required for a rigid lens to be implanted is about 5-6 mm. Such large incisions might give rise to various wound-related problems, including infection, wound leak and astigmatism. During the last years small incision surgery has become increasingly popular among ophthalmic surgeons. The problems indicated above are eliminated with such a technique which in addition allows less restricted early postoperative physical activity and more rapid optical rehabilitation. The phacoemulsification technique for removing the natural lens, while the major part of the capsule bag is maintained, was one essential step in the development of the small incision technique. These techniques involve implanting intraocular lenses through incision as small as about 2 mm and therefore, lenses to be used in these procedures have in common the feature of being deformable to a cross-section area small enough to match the small incision. The development of such lenses is therefore another essential step. A number of lens materials which fulfill this criteria, at least to some extent, have been suggested, for instance soft silicone materials which can be deformed, for instance folded or rolled-up, prior to insertion, and hydrogels, which are deformed and dehydrated to over-all small size prior to insertion and which in contact with aqueous humor inside the eye swell to the desired size.
Whilst the advantages of elastomeric silicone IOLs is well established, these lenses have some limitations, in particular silicones have a lower refractive index than PMMA (1.49), which has been adopted as the standard for IOL materials.
A further consequence of the lower refractive index of the silicone elastomer is the requirement for a thicker lens for any given dioptre than is necessary for e.g. PMMA. This factor taken together with its high rubber elasticity, results in its rapid and powerful recovery from folding, which is undesirable in the context of its use for posterior chamber lenses.
To overcome some of these disadvantages alternative flexible lens materials have been sought which combine a high refractive index with a lower elasticity. Acrylic polymers have been favoured because of their ease of preparation, high level of atacticity - ensuring low crystallinity, good processing characteristics, high optical quality and long term stability to UV.
A typical method of producing such acrylic polymers is by copolymerisation. Thus in U.S. Pat. No. 5,290,892 (Nestle SA) is reported the preparation of copolymers of 2-phenylacrylate and 2-phenylethylmethacrylate for use in the manufacture of IOLs. These polymers have refractive indices close to 1.55, glass transition temperatures (Tg) near to 37.degree. C. and an elongation of 200%.
I have now found that new improved materials for the preparation of intraocular lenses can be prepared from blends of certain polyacrylate-based polymers. The invention is accordingly related to the preparation of such homogenous blends with desired optical and mechanical characteristics as well as the use of such materials for the preparation of intraocular lenses.
In theory, depending on the thermodynamics of the interactions between the component polymers of a mixture and the mixing kinetics, polymer blends may be homogeneous or heterogeneous. A homogeneous blend of amorphous polymers is a single phase system which is totally transparent and has other physical prope
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Michl Paul R.
Pharmacia & Upjohn Groningen BV
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