Biocompatibility of polyvinylalcohol gel as a vitreous substitute

Polyvinylalcohol (PVA) hydrogel cross-linked by gamma irradiation was assessed as a possible vitreous substitute. From a series of experiments, rise of intraocular pressure and inflammatory changes in the vitreous cavity after operation were observed in some cases. Crab-eating macaques were used for this experiment. PVA gels were injected into vitreous cavity after vitrectomy and followed clinically by opthalmoscopy, tonometry, fundus photography, electroretinogram (ERG), chemotaxis, and flare cell meter. Histopathologic examination by light and electron microscopy was performed after 3 months. As a result, there were no significant changes in ophthalmoscopic findings. No abnormal rising of intraocular pressure (IOP) was recognized. ERG did not show meaningful amplitude weakness. From the photon counting of flare cell meter, significant break of blood-aqueous barrier and blood-retinal barrier was not observed. Histopathologic examination revealed that all layers of the retina were intact and no loss of tissue was evident. However, in PVA gel-injected eyes, some vacuolations of the inner retina were found in some specimens. To conclude, PVA gel was well tolerated in these experiments. The gel with a network similar to the vitreous body showed the best biocompatibility, though it is necessary to investigate the biocompatibility for the long-term. PVA gel is a good candidate for a vitreous substitute.