Replacement of the entire anterior segment of the eye is a very ambitious and complex endeavor and it is not known whether the retina remains functional when the anterior structures have been removed. We used routine histo-pathologic evaluation and electroretinographic measurements to determine the structural and functional status of rabbit retinas following surgical removal of the internal anterior structures (iris, ciliary body, and lens) and replacement of the vitreous with silicone oil. In some cases, we were able to record both a scotopic and a photopic electroretinographic response as long as 15 weeks after complete removal of the internal anterior segment structures. Although many hurdles remain and more efficacious surgical techniques and biomaterials need to be developed, our results suggest that, in the rabbit, the retina may continue to function in the absence of critical anterior segment structures.

To further the development of a sclera-attached anterior segment prosthesis we investigated the biocompatibility of expanded polytetrafluoroethylene following its surgical implantation into the rabbit sclera. Thin sheets (250 mu m) of expanded polytetrafluoroethylene were cut into pieces measuring either 2x2, 2x4, 2x8, or 4x8 mm. The pieces were sterilized and placed individually within surgically prepared pockets in the sclera of rabbit eyes. Animals were sacrificed for routine histopathologic evaluation and transmission electron microscopic study of the eyes at 7 days, 14 days, 1 month, and 4 months following surgical implantation. The implants demonstrated excellent compatibility with the sclera and, by 14 days following implantation surgery, exhibited histiocytes, fibroblasts, and blood vessels infiltrating the internodal spaces of the highly porous material. The number of cells and the amount of extracellular matrix material deposited in the implants appeared to increase with time. Transmission electron microscopic studies revealed deposition of collagen within the implants. Our results suggest that expanded polytetrafluoroethylene has potential for use in the development of a sclera-attached prosthetic device.

We have studied the graft rejection of bovine lamellar cornea transplanted onto the rabbit cornea. In addition, the effect of inhibitors of arachidonic acid metabolism and immunosuppressive agents on this heterolamellar corneal transplant was investigated. The corneal lamellar transplant treated with saline were rejected at 9 +/- 1.4 day with 100% rejection rate. The postsurgical conjunctival hyperemia and edema occurred within 2-3 days. Corneal neovascularization took 5 to 9 days to reach the region of the graft. Intramuscular cyclosporin A (25mg/kg/day) and dexamethasone (0.1%) applied topically for 20 days (t.i.d.) inhibited the corneal opacity, edema, neovascularization and graft rejection. Topical Dexamethasone in the ipsilateral eye prolonged survival of grafts in the contralateral (untreated) eye. Cyclosporin A and dexamethasone probably inhibited the graft rejection process by their immunosuppressive action. Indomethacin and BW755C, respective cyclooxygenase and lipoxygenase inhibitors, applied topically did not inhibit graft rejection process while inhibiting postsurgical inflammatory response.