An uveoscleral shunt device for refractory glaucoma studied in rabbits

Abstract

Abstract: : Purpose: The uveoscleral shunt device consists of a small tube which is similar to those tubes of drainage implants. Drainage implants connect the anterior chamber with a plate that is attached to the sclera behind the equator of the eye. The uveoslceral shunt does not connect the anterior chamber with the exterior of the eye. Instead, the uveoscleral shunt device leads the aqueous into the choroid at or behind the pars plana of the ciliary body. From previous experiments, it is knwon that the uvea has a negative pressure and can transport fluids out of the eye. The uveoscleral shunt takes advantage of this mechanism. In a few blind eyes of patients, the uveoscleral shunt was implanted and was able to reduce the intraocular pressure in several of these cases. The animal experiment was then performed to study the effect of such a tube in the choroid histopatholgically. Methods: Pigmented female rabbits were used. Tubes made of silicone were used and implanted in such a way that they connected the anterior chamber with the uvea in the area of the pars plana. Open (group 1) and closed (group 2) tubes were implanted. Eyes were enucleated for histopathologic examination at days 4, 6, 10 and 21. Results: The surgical procedures had a few complications involving the structures of the anterior chamber including contact to the inner aspect of the cornea, iris incarcerations and endothelialisation of the tube. The posterior portion of the tube in the choroid elicited no foreign–body reaction. Instead, a thin layer of fibrous tissue without much in the way of acute or chronic inflammation surrounded the silicone tubes over time. This reaction was more pronounced in eyes that had received the closed tube beginning from day 6 following surgery (group 2). In group 1, this reaction was less marked and started from day 10 on. Conclusions: It appears that a silicone tube is well tolerated in the choroid. No acute inflammatory response was initiated. Fibrosis surrounding the implant may compromise the drainage function. This effect is more evident in cases where no aqueous reaches the uvea, making it likely that the aqueous, its flow or both factors contribute to an inhibition of fibrosis. It remains to be seen how strong this potentially compromising effect will be present in patients.

Keywords: intraocular pressure • aqueous • choroid