Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Corneal implant
Patent
1996-05-16
1998-02-03
Jones, Mary Beth
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Corneal implant
A61F 214
Patent
active
057139571
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the field of ophthalmology, and more particularly is directed to corneal implants.
The cornea is a complex layered structure comprising an outer layer of epithelial cells, Bowman's membrane posterior of the epithelial layer, the stroma posterior of the Bowman's membrane, Descemet's membrane posterior of the stroma, and the endothelium immediately posterior of Descemet's membrane. A number of surgical procedures involve implanting a lens structure into or onto one or more of these corneal components. In one form of eye surgery, the epithelial cell layer is removed and a corrective lens structure is placed and secured at the location where the cells are removed. In another form of eye surgery, a portion of the layer of epithelial cells is removed and a wedge-shaped annulus from Bowman's membrane and the underlying stroma is remove& An incision is then made from the posterior end of the resulting groove radiating outwardly in an annular zone to define a flap. A corrective lens structure is then attached by inserting the wing of the lens structure beneath the cornea/flap and sunning it in place. A corrective lens structure can also be placed entirely within the stroma. This surgical procedure involves making an incision in the cornea to gain access to the stroma and also involves disrupting the stroma by placing a lens structure therein.
The aforementioned corneal corrective surgeries are employed for the treatment of severe visual disturbances such as those associated with excessive or insufficient corneal curvature, traumatic injury to the cornea, for contact lens intolerant patients and the like. These procedures are generally known as keratoplasties.
It has previously been recognized that implanted corneal prostheses must be effectively anchored to cornea/tissue, and provide permeability to gas, metabolites and nutrients (particularly glucose). Apart from surgical techniques and mechanical fixation with sutures and the like to fix implants in place, previous proposals have employed attachment factors which coat the implant (see, for example, U.S. Pat. Nos. 4,715,858; 5,171,381; and 5,192,316). With regard to questions of permeability, prior proposals have included the use of hydrogel forming polymers of high-water content on the basis of their permeability to glucose and gas exchange characteristics. We have found that hydrogels, whilst porous to glucose, nutrients and metabolites, are not porous toward protein. Hydrogels and like "porous" polymers block the free movement of proteins and other high molecular weight tissue fluid components and so compartmentalize the tissue anterior to a corneal implant from that beneath the implant. This has significant deleterious effects as will be hereinafter described. Hydrogels also lack the requisite mechanical properties necessary for ocular implants. For example, hydrogel ocular implants described in Australian Patent No. 623137 shrink by about 22% (that is shrinkage from initial volume) when placed in physiological saline (see page 16, lines 19 to 24 of Australian Patent No. 623137). Clearly such materials would not be appropriate for implantation into the eye. Moreover, cells attach very poorly to hydrogel polymers with the result that epithelial recolonization of hydrogel implants would be impeded.
It has also previously been proposed to provide corneal implants with holes for the passage of nutrients and fluids from the lower layers of the cornea through the implant to the upper layer of the cornea. These proposals suffer the disadvantages that the holes provided are too small to allow passage of proteins, or alternatively, are of such a diameter that visual acuity is effected either by direct distortion of light passing through the implant or by tissue ingrowth into the implant obscuring vision.
We have now surprisingly found that the flow of high molecular weight tissue fluid components such as proteins and glycoproteins (for example, growth factors, peptide and protein hormones, and proteins associated with the transport of essentia
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Holden Brien A.
Johnson Graham
O'Leary Dan
Schindhelm Klaus
Steele John Gerard
Ciba Vision Corporation
Jones Mary Beth
Lee Michael U.
Meece R. Scott
The Commonwealth of Australia Commonwealth Scientific and Indust
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