Fig. 5. Ultrastructure of human vitreous. Although specimens were centrifuged to concentrate structural elements, there were no membranes or membranous elements. Only collagen fibrils were detected. There were also bundles of parallel collagen fibrils such as the one shown here in cross section (arrow). (From Sebag J, Balazs EA: Morphology and ultrastructure of human vitreous fibers. Invest Ophthalmol Vis Sci 30:187, 1989.)