Ultrastructure of hyaluronic acid and collagen in the human vitreous

The ultrastructure of hyaluronic acid (HA) and collagen in the human vitreous was investigated. After fixation with 4% glutaraldehyde and 0.1% cetylpyridinium chloride (CPC), sectioned blocks of retina and attached vitreous body were stained with 500 ppm ruthenium red (RR) in 1.25% glutaraldehyde, postfixed with 500 ppm RR in 2% OsO4, and embedded in Epon 812. In addition, collagen II immunostaining was done. Collagen fibrils were coated with amorphous material believed to be HA. No amorphous material was seen in the fibrils in the cortical areas adjacent to the retina, but the amount of material gradually increased toward the center of the vitreous body. By using anticollagen II antibody, we showed the presence of collagen II, often oriented perpendicular to the surface. The central vitreous demonstrated some dense materials that were collagen fibrils packed into bundles of parallel fibrils. In summary, collagen fibrils contained little HA in the cortical areas adjacent to the retina, but they were packed into bundles of parallel fibrils in the central vitreous.