Experimental vitreous tamponade using polyalkylimide hydrogel

Abstract

Purpose: To evaluate polyalkyl-imide 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, polyalkyl-imide (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:Polyalkyl-imide 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.

A new model for in vitro testing of vitreous substitute candidates

“…The explanted retinas were less affected in minor areas that may not have been in direct contact with the gel, although this is difficult to discern due to the loss of gel in the preparation and sectioning procedures. This is in accordance with previous studies that demonstrated pathological changes in the retina in vivo, primarily in parts more likely to have been in direct contact with the gel [37], suggesting at least in part a toxic or immunological response. Recently, clinical use of Bio-Alcamid® in reconstructive surgery has become increasingly controversial due to late complications such as inflammation, infection and excessive capsule formation [45][46][47][48].…”

“…In two recent papers our group investigated two promising potential intravitreal substitutes in an in vivo rabbit model: Polyalkylimide (Bio-Alcamid®) [37] and a poly (ethylene glycol) (PEG) hydrogel [38].…”

“…The in vivo trials showed favorable biocompatibility but inadequate stability in vivo using PEG where the substance was largely tolerated with minor changes in retinal cytoarchitecture and GFAPupregulation, and minor electrophysiological changes [38]. On the other hand, Bio-Alcamid® displayed suitable physical properties but caused severe functional and morphological retinal damage with increased GFAP expression and cell death (TUNEL) [37].…”

“…Bio-Alcamid® caused severe retinal damage in vivo [37] and negatively affected the morphology of cells and cell layers, induced cell death and induced GFAP upregulation very early in vitro. Some of the variability in cytoarchitecture for retinas treated with Bio-Alcamid® might have been due to uneven coverage of the gel.…”

Safety of Medium-Chain Triglycerides Used as an Intraocular Tamponading Agent in an Experimental Vitrectomy Model Rabbit

“…Various substances and approaches have been explored, but to date, clinically available alternatives to conventional tamponades (gas and silicone oil) are still very limited. [12][13][14][15][16][17][18] Identifying and developing a novel intraocular tamponading agent is a challenging task, albeit with a large therapeutical potential. The first step of this approach is to determine if the agent would be toxic to the retina or other ocular tissues.…”