Experimental vitreous tamponade using polyalkylimide hydrogel.

PURPOSE: To evaluate polyalkylimide as a possible vitreous tamponading agent.
METHODS: A 20-gauge pars plana vitrectomy and posterior vitreous detachment were performed in the right eye of six pigmented rabbits. Approximately 1 ml of viscoelastic gel, polyalkylimide (Bio-Alcamid) was thereafter injected into the vitreous space. Full-field ERG and intraocular pressure (IOP, Tonopen) was measured pre-and postoperatively at regular intervals up to 28 days. At day 6 or 28, the rabbits were sacrificed and the eyes were examined macroscopically, photographed, and prepared for histological examination with routine microscopy.
RESULTS: The viscoelastic hydrogel was successfully injected, and remained translucent with preserved gel properties throughout the postoperative period. The postoperative IOP was unchanged compared to preoperative values. Five of six eyes displayed retinal edema or pigmentary changes centrally while the periphery appeared intact. ERG recordings showed a radical decrease in rod- and cone-derived B-wave amplitudes. Histological examination confirmed varying degrees of edema combined with neuronal cell death within the retinal layers in the central part of the fundus, while the peripheral part appeared intact.
CONCLUSION: Polyalkylimide displays favourable physical properties when used as a vitreous tamponade. However, the hydrogel causes functional and morphological retinal damage when in direct contact with the inner retina. Possible pathological mechanisms include osmotic imbalance and direct toxic effects, and modification of biochemical properties is warranted before clinical use will be possible.