Abstract
Abstract: :
Purpose: To evaluate surface diathermy as a means of permanently breaking down the blood– retinal barrier, thus facilitating transscleral drug delivery from a subtenons nonerodible sustained drug delivery system. Methods: A PVR model was established by injecting 300,000 cultured corneal fibroblasts into the vitreous cavity of both eyes of 2kg albino rabbits. A day was allowed to elapse in order to allow time for implantation of the cells on the retinal surface. A small superior peritomy was then fashioned in each eye, and several (average 5) surface diathermy applications were made at the equator of the globe in a small circular pattern. Nonerodible ethylene vinyl acetate copolymer explants ( 70% ethylene/30% vinyl acetate, 5 x 10 x 1mm in size) containing a diffusely distributed 10% concentration of 5–fluorouracil were placed in the subtenons space over the diathermy marks. Conjunctiva was then sutured so as to cover the explants. A sham operation was done in the opposite eye, in which a similar sized piece of a silicone strip was placed in the subtenons space over the diathermy marks. Eyes were then observed and photographed to confirm whether or not traction retinal detachments developed in the region of the medullary ray. Selected eyes underwent ERG testing. Histology was eventually obtained. In a separate experiment, surface diathermy applications were made in a similar pattern to that described above. After allowing conjunctiva to heal, subtenons fluorescein sodium solution was injected in the area of the diathermy marks. Observations were made and fundus photographs taken regarding visible penetration of the fluorescein into the vitreous cavity. Results: None of the eyes with the fluorouracil containing ethylene vinyl acetate explants developed traction retinal detachments. Approximately 75% of the controls did develop traction detachment of varying degree. The explants appeared to be well tolerated in all eyes. No ERG abnormalities were found in the studied animals. In the experiment involving subtenons fluorescein, the fluorescein appeared to penetrate readily into the vitreous cavity from the diathermy marks, as compared to surrounding areas of the fundus away from the diathermy. Conclusions: Surface diathermy may be a means of breaking down the blood–retinal barrier by focally obstructing choroidal blood flow and damaging the overlying pigment epithelium, thus allowing free diffusion of subtenons administered drugs into the vitreous cavity. Based on previously published pathology, this effect should be permanent. This might allow for sustained drug delivery of agents from the subtenons space, which currently require intravitreal injection.
Keywords: pharmacology • proliferative vitreoretinopathy • age-related macular degeneration