An evaluation of methylated collagen as a substitute for vitreous and aqueous humor

Purpose:To evaluate ocular tolerance of methylated collagen gel injected intravitreally and into the anterior chamber. Methods: Methylated collagen (type I/III) was tested in New Zealand white rabbits. Vitreous cavity: After pars plana vitrectomy, methylated collagen gel was injected intravitreally. The eyes were examined clinically; electroretinogram recordings were made before and after surgery. Vitreous samples were taken for immunological analysis for the presence of the injected collagen. The rabbits were sacrificed 6 months after surgery; the retina was evaluated by light microscopy. Anterior chamber: In another group of rabbits, methylated collagen gel (0.2 ml, 0.1 ml, or 0.05 ml) was injected into the anterior chamber after paracentesis. The eyes were examined with a slit lamp; intraocular pressure was measured postinjection. The rabbits were sacrificed after 4 months; the corneas were evaluated histologically. Results: Vitreous cavity: The fundus view was clear for 6 months after intravitreal injection. Scotopic and photopic electroretinograms were normal in 6/7 eyes; one eye experienced a mild decrease one month postoperatively. No abnormal changes were found in the retinal histology. Anterior chamber: Some corneas were hazy and edematous around the injection site for one week. The injected collagen appeared in bundles, patches, and little pieces in the anterior chamber with precipitates on the corneal endothelium, pupillary margin, and the anterior capsule of the lens. The collagen diminished gradually, without causing permanent opacity. Histologically, the corneal endothelium in the eye which received 0.2 ml collagen showed a mild distention of the mitochondriae and vesicle formation between endothelial cells under transmission electron microscope. Conclusion: Methylated collagen gel was tolerated by the eye after intravitreal injection. Localized temporary clinical and mild ultrastructural corneal changes were observed after anterior chamber injection.