Morphology and ultrastructure of human vitreous fibers

Significant alterations in vitreous structure occur with aging and disease. There is controversy as to the nature of the normal structure of the vitreous and no studies have correlated macroscopic structure with ultrastructure in the same eyes. Twenty-eight fresh, untreated human eyes were examined after removal of the sclera, choroid and retina. Dark-field slit illumination of the whole vitreous revealed the presence of macroscopic fibrous structures. The fibers had an antero-posterior orientation with anterior insertions at the vitreous base and posterior insertions in the premacular vitreous cortex. Transmission electron microscopy demonstrated the presence of collagen fibrils and no membraneous structures. Parallel collagen fibrils packed in bundles were also detected. Macroscopic vitreous fibers most likely result from alteration of the hyaluronic acid-collagen complex with aggregation of collagen fibrils into bundles as seen on electron microscopy. Identifying the mechanisms underlying this process of fiber formation could clarify the pathogenesis of vitreous liquefaction and the pathophysiology of posterior vitreous detachment.