Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-06-12
2004-03-09
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S292300, C526S292500, C526S307500, C526S312000, C526S323100, C623S006110, C623S006560, C359S642000
Reexamination Certificate
active
06703466
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to intraocular lenses. In particular, the present invention relates to foldable intraocular lens optics having a reduced risk of posterior capsule opacification.
BACKGROUND OF THE INVENTION
Foldable intraocular lens (“IOL”) materials can generally be divided into three categories: silicone materials, hydrogel materials, and non-hydrogel acrylic materials. Many materials in each category are known. See, for example, Foldable Intraocular Lenses, Ed. Martin et al., Slack Incorporated, Thorofare, N.J. (1993). Biocompatibility varies among different IOL materials within and among each category.
One measure of biocompatability for an IOL can be the incidence of posterior capsule opacification (“PCO”). A number or factors may be involved in causing and/or controlling PCO. For example, the design and edge sharpness of an IOL may be a factor. See, Nagamoto et al., J. Cataract Refract. Surg., 23:866-872 (1997); and Nagata et al., Jpn. J. Ophthalmol., 40:397-403 (1996). See, also, U.S. Pat. Nos. 5,549,670 and 5,693,094. Another factor appears to be the lens material itself. See, for example, Mandle, “Acrylic lenses cause less posterior capsule opacification than PMMA, silicone IOLs,” Ocular Surgery News, Vol. 14. No. 15, p.23 (1996). See, also, Oshika, et al., “Two Year Clinical Study of a Soft Acrylic Intraocular Lens,” J. Cataract. Refract. Surg., 22:104-109 (1996); and Ursell et al., “Relationship Between Intraocular Lens Biomaterials and Posterior Capsule Opacification,” J. Cataract Refract. Surg., 24:352-360 (1998).
One method of addressing the PCO problem involves administering a pharmaceutical agent to the capsular bag area at the time of, or immediately after, extracapsular cataract extraction. See, for example, U.S. Pat. Nos. 5,576,345 (pharmaceutical agent=the cytotoxic agent taxol or an ophthalmically acceptable derivative); 4,515,794; and 5,370,687. Alternatively, the pharmaceutical agent may be tethered to the surface of the IOL material. See, for example, U.S. Pat. No. 4,918,165. The pharmaceutical agents are intended to kill or prevent the growth of proliferating cells that might cause PCO or “secondary cataracts.” Yet another method involves the physical destruction or removal of lens epithelial cells. See, Saika et al., J. Cataract Refract. Surg., 23:1528-1531 (1997).
Another method of addressing PCO is the prophylactic laser therapy is method disclosed in U.S. Pat. No. 5,733,276. According to this method, the lens capsule is irradiated with laser irradiation to destroy cells that remain in the lens capsule after extraction of a cataract.
Other methods theorized for reducing the risk of PCO involve adhering the posterior capsule to the IOL at the time of implantation, as in U.S. Pat. No. 5,002,571. According to the '571 patent, a non-biological glue or, preferably, a biological glue, such as fibrin, collagen, or mussel glue, is used to adhere the posterior lens capsule to the posterior surface of an. IOL. The glue may be applied over the entire posterior surface of the IOL or just as an annulus around the outer perimeter of the posterior surface of the IOL.
In contrast, U.S. Pat. No. 5,375,611 discloses a method of reducing the risk of PCO by preventing the adherence of the posterior capsule to the IOL. According to the '611 patent, the posterior surface of the lens capsule itself is chemically modified at the time of extracapsular cataract extraction. The chemical modification is achieved by depositing a water-insoluble stable or permanent layer of a cell attachment-preventing compound onto the posterior surface of the lens capsule. The stable or permanent layer may be a polymer, such as polyethylene glycol, polysaccharides, polyethylenepropylene gylcol, and polyvinyl alcohol derivatives.
What is needed are foldable IOLs having a reduced risk of PCO.
SUMMARY OF THE INVENTION
The present invention provides such foldable IOLs. According to the present invention, foldable IOL optics are prepared so that they have a glassy surface and rubbery bulk state. Specifically, the IOL optics have a T
g
(bulk) of about −20 to +25° C., but a T
g
(surface) of +30° C. or higher. The IOL optics of the present invention also have an elastic modulus (surface) of about 800 MPa or greater.
Without being bound to any theory, it is believed that IOL optics having mobile surfaces are more susceptible to PCO than those that have less mobile surfaces. IOL optics with rigid surfaces and rubbery cores exhibit improved adhesion to the capsular bag. The rubbery core allows the optic to conform more closely to the shape of the capsule, thus maximizing the contact area between the optic and capsule. At the same time, the rigid optic surface allows sustained or more complete contact with the capsular bag than mobile surfaces.
DETAILED DESCRIPTION OF THE INVENTION
Unless indicated otherwise, all component amounts are presented on a % (w/w) basis.
As used herein, “elastic modulus (surface)” is the elastic modulus determined on the IOL optic surface using an atomic force microscope (using cantilevers having a spring constant of at least 50 N/m, calibrated by the spring against spring method) under normal laboratory (i.e., ambient) conditions. The elastic modulus (surface) value is calculated as the average of elastic modulus (surface) values obtained from at least nine randomly chosen points across the IOL optic surface.
As used herein, “T
g
(surface)” is the extrapolated onset of the glass transition of the IOL optic determined using a Micro-Thermal Analyzer 2990 (TA Instruments), calibrated with amorphous polymers at a rate of heating of 10° C./s, under normal laboratory (i.e., ambient) conditions. The T
g
(surface) value is calculated as the average of T
g
(surface) values obtained from at least nine, preferably at least 18, randomly chosen points across the IOL optic surface.
As used herein, “T
g
(bulk)” is the midpoint of the heat capacity increase at the glass transition for a sample of the IOL optic material, measured by differential scanning calorimetry at 10° C./min. under normal laboratory conditions using nitrogen or air as a purge gas.
According to the present invention, IOL optics are prepared so that they have a T. (bulk), which affects the optic's folding and unfolding characteristics, of about −20 to +25° C., but a T
g
(surface) of +30° C. or higher. Preferably, the IOL optic has a T
g
(bulk) of about −5 to +18° C. and a T
g
(surface) of +35° C. or higher. The IOL optics of the present invention also have an elastic modulus (surface) of about 800 MPa or greater, preferably about 1000 MPa or greater.
In addition to the T
g
(surface), T
g
(bulk) and elastic modulus (surface) properties defined above, the IOL optics of the present invention have an elongation of at least about 150%, preferably at least 200%, and most preferably about 300-600%. This property indicates that the IOL optic generally will not crack, tear or split when folded. Elongation of polymer samples is determined on dumbbell-shaped tension test specimens with a 20 mm total length, length in the grip area of 4.88 mm, overall width of 2.49 mm, 0.833 mm width of the narrow section, a fillet radius of 8.83 mm, and a thickness of 0.9 mm. Testing is performed on samples at ambient conditions using an Instron Material Tester (Model No. 4442 or equivalent) with a 50 Newton load cell. The grip distance is set at 14 mm and the crosshead speed is set at 500 mm/minute, and the sample is pulled until failure. The elongation (strain) is reported as the displacement at failure relative to the original grip distance in percentage terms.
The IOL optic has a refractive index of at least about 1.45, and preferably at least about 1.50, as measured by an Abbe′ refractometer at 589 nm (Na light source).
The T
g
(surface), T
g
(bulk), elastic modulus (surface), elongation and refractive index are determined once all processing steps, such as any post-cure polishing or surface treatments (e.g., plasma treatment acco
Freeman Charles
Karakelle Mutlu
Menczel Joseph D.
Scott Robert A.
Alcon Inc.
Ryan Patrick M.
Zalukaeva Tatyana
LandOfFree
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