The underlying causes of glaucoma are not fully understood. However, it is known that elevated intraocular pressure is one of the symptoms associated with the development of glaucoma. Elevations of intraocular pressure can ultimately lead to impairment or loss of normal visual function due to damage to the optic nerve. It is also known that the elevated intraocular pressure is caused by an excess of fluid (i.e., aqueous humor) within the eye. The excess intraocular fluid is believed to result from blockage or impairment of the normal drainage of fluid from the eye via the trabecular meshwork.
The current drug therapies for treating glaucoma attempt to control intraocular pressure by means of increasing the drainage or "outflow" of aqueous humor from the eye or decreasing the production or "inflow" of aqueous humor by the ciliary processes of the eye. In some cases, patients become refractory to drug therapy. In other cases, the use of drug therapy alone is not sufficient to adequately control intraocular pressure, particularly if there is a severe blockage of the normal passages for the outflow of aqueous humor. Thus, some patients require surgical intervention to correct the impaired outflow of aqueous humor and thereby normalize or at least control their intraocular pressure. The outflow of aqueous humor can be improved by means of intraocular surgical procedures known to those skilled in the art as trabeculectomy procedures. These procedures are collectively referred to herein as "glaucoma filtration surgery."
The procedures utilized in glaucoma filtration surgery generally involve the creation of a fistula to promote the drainage of aqueous humor into a surgically prepared filtration bleb. Alternatively, filtration devices have been used to shunt aqueous humor via a cannula from the anterior chamber into a dispersing device implanted beneath a surgically created bleb. A number of designs for filtration implants are known. See, for example, Prata et al., Ophthalmol. 102:894-904 (1995) which reviews a variety of available filtration implants made from polypropylene, polymethylmethacrylate or silicone materials. See also, Hoskins et al., Ophthalmic Surgery 23:702-707 (1992).
Wound fibroplasia is a common cause of failure for glaucoma filtration devices. The fibroplasia results in encapsulation of the device, limiting aqueous humor outflow. There is a need for an improved glaucoma filtration device material which exhibits flexibility, is resistant to bioerosion and tissue adhesion, and does not elicit a significant immune response.