Biocompatibility response to modified Baerveldt glaucoma drains

Abstract

Glaucoma implants are designed to increase fluid outflow from the eye in order to decrease intraocular pressure and prevent damage to the optic nerve. The implant consists of a silicone tube that is inserted into the anterior chamber at one end and is attached at the other end to a silicone plate that is sutured to the outside of the globe beneath the conjunctiva. The glaucoma "implant" becomes a "drain" over the first 3 to 6 postoperative weeks as the silicone plate is enclosed by a fibrous capsule that allows a space to form into which fluid can drain and from which fluid can be absorbed by the surrounding tissues. Ideally, the size and thickness of the capsule (the filtering bleb) that surrounds the plate is such that the amount of fluid that passes through the capsule is identical to the amount of fluid produced by the eye at an intraocular pressure of 8 to 14 mmHg. The most common long-term complication of these implants is failure of the filtering bleb 2 to 4 years after surgery due to the formation of a thick fibrous capsule around the device. Micromovement of the smooth drainage plate against the scleral surface may be integral to the mechanism of glaucoma implant failure by stimulating low-level activation of the wound healing response, increased collagen scar formation, and increased fibrous capsule thickness. To test this hypothesis, we modified seven Baerveldt implants by adding porous cellular ingrowth material to the posterior surface of the drainage plate. Seven modified and five unmodified implants were placed in adult rabbit eyes. After 6 months, we found that the fibrous capsule around the modified implants was significantly thinner than the capsule surrounding the unmodified implants (p < 0.05), particularly on the surface between the porous ingrowth material and the sclera (p < 0.05). Although type I collagen predominated in the fibrous capsules around both types of implants, the amount of type III collagen in the capsules around the modified implants was significantly less than the amount around the unmodified implants (p < 0.05). We believe that these data suggest a reduction in the wound healing response to the modified implants, with greater stability of capsule thickness. Long-term studies are needed to verify that the stability of the capsules around the modified implants persists over a period of years, in which case this type of modification may prove useful in prolonging the functional life of these devices in the surgical treatment of glaucoma.

A Newly Designed Glaucoma Drainage Implant Made of Poly(styrene-b-isobutylene-b-styrene)

“…It is believed that the fibrotic and inflammatory reactions induced by biomaterials are a major determinant of success. [20][21][22] Other factors such as shape, flexibility, modulus, and texture could also be associated with erosion, extrusion, inflammation, and scarring. 20 Hypothetically, selecting a biomaterial and a design that produces minimal inflammation and fibrosis is a means to increase success.…”

Outcomes of Fornix-based Versus Limbus-based Conjunctival Incisions for Glaucoma Drainage Device Implant

“…20 However, the results of our study suggest that bleb formation, remodeling, and eventual IOP control in the setting of GDD implantation may be dependent on factors other than the site of conjunctival incision. For example, previous investigators have suggested that different implant material can activate a macrophage response in varying degrees that will determine the overall foreign body response 13 and thus bleb formation. Implant size and geometry can reduce bleb surface tension leading to less capsular fibrosis and improved filtration.…”

“…13 Stabilization of the implant to the scleral surface, 13 varying the timing and intensity of aqueous flow to the capsule, 14 size and shape of the implant, [15][16][17] and the use of antifibrotic agents 18 are all modifications that affect capsule fibrosis and subsequent IOP control. However, it is not known whether the proximity of the conjunctival incision affects capsule fibrosis and IOP control.…”

Conjunctival Expansion Using a Subtenon's Silicone Implant in New Zealand White Rabbits

“…Clearly, during the insertion of the silicone sponge into the subtenon space, injuries to the tissue can be minimized by paying close attention to the manipulation. The surgeon has to be careful during the insertion of the silicone sponge and the resection of the conjunctival tissues, not only to minimize the formation of buttonholes in the conjunctiva, but also because the insertion of the silicone material itself can induce inflammatory reactions 42. Consequently, inflammatory changes can develop in the conjunctiva, conjunctival hyperemia can persist, a thick conjunctival scar can form, and by developing a severe adhesion to other adjacent tissues, diplopia may develop, as well as other postoperative complications.…”