THE EFFECT OF RETINAL CRYOAPPLICATION ON THE VITREOUS

Purpose: The effect of retinal cryopexy on the vitreous was studied mo rphologically in an animal model. Methods: The retina and vitreous wer e frozen with single cryolesions on one eye and 24 contiguous cryolesi ons on the contralateral eye in 16 rabbits. The cryoprobe was applied to the sclera from 3mm to 6mm posterior to the limbus at -60 degrees C until ophthalmoscopically visible whitening occurred. Two animals wer e killed on the first day; the third day; after 1, 2, and 4 weeks; and after 2, 3, and 6 months after surgery. The eyes were enucleated and prepared by the celloidin embedding method. Each 200-mu m section was examined by light microscopy. Areas of the specimens were dissected an d studied by scanning and transmission electron microscopy. Results: S ingle cryolesions did not have a significant generalized effect on the vitreous. Evidence of local collagen destruction and dispersion of ce lls was found near the area of cryoapplication. Contiguous cryoapplica tion led primarily to increased density in the vitreous and subretinal edema. The vitreoretinal border was invaded by mononuclear cells cont aining pigment granules. Thickened collagen fibers were attached to th e coagulated retina in a perpendicular manner and traversed the whole vitreous body. After 4 weeks the increased vitreous density slowly dim inished, and preretinal capillaries surrounded by vitreous collagen st arted to proliferate from the vitreoretinal interface, After 6 months central vitreous collagen fibers looked normal. In the area of cryoapp lication, vitreoretinal membrane formation had occurred. Conclusion: S ingle cryolesions have no significant effect on the vitreous. Multiple cryolesions lead to neovascularization soon after the procedure (1 mo nth) and membrane formation later (6 months after the procedure). This supports the concept that the extensive use of cryopexy in human reti nal surgery could contribute to the development of proliferative vitre oretinopathy.