Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2001-05-03
2003-03-18
Hayes, Michael J. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C128S898000, C623S006560
Reexamination Certificate
active
06533769
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to cataract surgery, specifically to a method for preventing proliferation of remaining lens epithelial cells after cataract surgery.
BACKGROUND OF THE INVENTION
The crystalline lens of the human eye is located in the posterior chamber between the posterior iris surface and the vitreous body. It is a biconvex transparent tissue without nerves and blood vessels, weighing approximately 0.2 g. The lens is enveloped in a capsule, a structureless, transparent and elastic membrane bag. Approximately 80 zonular fibres, extending between the capsule and the ciliary body, suspend the lens. The inside of the lens capsule consists of lens epithelial cells and lens fibres. The lens epithelial cells form a monolayer underlying the capsule from the anterior pole to the equator of the lens. These cells continue to undergo cell mitosis throughout life in the area located between the anterior pole and the lens equator. The lens epithelial cells that underwent cell mitosis gradually move toward the lens equator and differentiate into lens fibres. These cells make up the rest of the lens. New layers of fibre cells are constantly formed on top of those previously formed. The older fibre cells become denser and during the 3
rd
decade of life a hard nucleus is formed in the middle of the human lens, consisting of old dehydrated fibre cells.
A cataract is defined as every form of opacity in the lens or its capsule; the lens becomes cloudy, resulting in a loss of visual ability. A cataract is a painless phenomenon, but decreases the quality of life if the lens is not surgically extracted and replaced by an artificial lens.
When the lens is surgically extracted, an incision is made in the anterior part of the eye, i.e., the cornea or the sclera. Then, a viscoelastic material is usually introduced into the anterior chamber to maintain the anterior chamber depth during surgery. An opening is made in the lens capsule by a procedure called capsulorhexis.
Following capsulorhexis, the lens is removed according to one of two principles: extracapsular cataract extraction (ECCE)—the cataractous lens is squeezed out through an opening in the anterior lens capsule and then removed through a 10-12 mm corneal incision, or phacoemulsification—the cataractous lens is dissolved with a special instrument, phaco-probe, by high frequency sonification and rinsed out through a 3-4 mm corneal incision.
Remaining parts of the lens, i.e. lens fibres and lens epithelial cells, are then removed using an irrigation and aspiration device. After complete removal of the lens, the lens capsule is filled with a viscoelastic material and an artificial lens is implanted into it.
Dyeing of the anterior lens capsule has been used to facilitate capsulorhexis in advanced/white cataract, to enhance critical steps during phacoemulsification and to perform capsulorhexis of the posterior lens capsule. Earlier studies have evaluated dyes, such as crystal violet, fluorescein, and indocyanine green, for dyeing the anterior lens capsule. Some dyes are applied by injection under the anterior surface of the capsule. Others are applied by a certain technique in which the anterior chamber is filled by air, and the dye is applied on top of the anterior surface of the capsule. After a while, the dye is washed away by irrigation/aspiration and the anterior chamber is filled by a viscoelastic solution followed by capsulorhexis.
After cataract surgery, the most common postoperative complication is posterior capsule opacification (PCO) which has the clinical and economic significance to be considered as an important public health problem. Studies report that the incidence of PCO is ranging from 20% to 40% after approximately 4 years after surgery. Migration and proliferation of remaining lens epithelial cells is the main cause of PCO. These cells grow from the peripheral parts of the capsule onto the posterior capsule and continue toward the axial region. Impaired visual acuity is the result caused by cell migration, proliferation and aggregation, the production of extracellular matrix, fibrosis and wrinkling of the lens capsule.
In the current clinical standard, patients who develop PCO are treated by YAG laser to capsulotomy. In this procedure a YAG laser disrupts the opacified lens capsule and the visual axis is cleared. However, YAG laser capsulotomy exposes patients to the risk of complications that can lead to severe visual impairment or loss of vision, such as retinal detachment, pupillary block glaucoma and cystoid macular edema. Other complications associated with YAG laser capsulotomy include damage to implanted intraocular lenses resulting in glare and photophobia, dislocation of intraocular lenses, iritis, vitritis, corneal edema, iris damage and rupture of the anterior hyaloid.
From an economic point of view, the treatment of PCO is ranked one of the highest of the medical costs in the U.S.A. Thus, development of a procedure to prevent PCO reduces the medical costs related to YAG laser capsulotomy, including the costs for the treatment, its complications, and YAG laser equipment. Accordingly, there is a great need for a way to prevent PCO.
Mechanical and pharmaceutical methods to prevent PCO by removing or destroying residual lens epithelial cells have been developed. However, none of them has been proved to be practical, effective, and safe enough for routine clinical practice.
Capsular polishing, aspiration of residual lens epithelial cells, ultrasound combined with aspiration, cryocoagulation, and osmolysis are examples of methods that have been developed and shown to remove or destroy remaining lens epithelial cells, but none of these methods have been proven to prevent PCO effectively.
The design of the artificial intraocular lenses (IOL), such as the shape, size and materials of the IOL implanted during cataract surgery has also been shown to affect the development of PCO. It has been shown that a sharp bend in the capsule, created by a capsule tension ring or an IOL with sharp optic edges, may induce contact inhibition of lens epithelial cell migration on the capsule.
Various anti-metabolites such as doxorubicin, methotrexate, mitomycin, daunomycin/daunorubicin, 5-fluorouracil and colchicine are effective in inhibiting lens epithelial cells proliferation in vitro. However, in vivo animal studies have shown that there are toxic side effects in the tissues of the eye when anti-metabolites are used in sufficiently high concentration to inhibit lens epithelial cells proliferation. In attempts to avoid side effects on other ocular tissues an immunotoxin specifically inhibiting proliferation of lens epithelial cells has been evaluated. The anti-lens epithelial cell monoclonal antibody binds specifically to lens epithelial cells and carries ricin or saporin that kill proliferating cells. In the experimental studies, antibodies against human antitransferrin and FGF have been used as antibodies against lens epithelial cells. However, no conclusive results have been obtained.
Another pharmacological approach is to separate lens epithelial cells from the lens capsule. Ethylenediamine tetraacetic acid (EDTA) was included in an irrigative solution and a simulated extracapsular cataract extraction was performed to separate lens epithelial cells. In other attempts, EDTA was used with a viscoelastic material (U.S. Pat. No. 5,204,331 to Nishi et al., 1993), or simply introduced into the lens capsule. When an EDTA solution was included in an irrigative solution and a simulated extracapsular cataract extraction was performed in cadaver eyes, the anterior lens epithelial cells could be separated. EDTA seems not to be more efficient than other agents evaluated in PCO prevention.
Enzymes such as trypsin and DISPOSE (protease) have also been evaluated for separation of lens epithelial cells. When a 2% trypsin solution was included in an irrigative solution and a simulated extracapsular cataract extraction was performed in cadaver eyes, lens epithelial cells were stripped in places. The cell sepa
Han Mark
Hayes Michael J.
Jenkens & Gilchrist P.C.
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