Patients with diabetes experience vitreous degeneration, characterized by "precocious" liquefaction and posterior vitreous detachment. Biochemical studies have detected that hyperglycemia alters vitreous collagen, changes that might be responsible for the observed vitreous degeneration. This study was undertaken to identify if there are morphological changes within the vitreous of diabetic patients that are consistent with the biochemical data and to identify how these could underlie the observed clinical phenomena. Ten eyes from 5 humans (4 normals aged 6, 11, 56, 82; 1 aged 9 with type I diabetes) were obtained at autopsy. Eyes were dissected in the fresh state and studied by dark field slit microscopy without fixatives or dyes. In normals, a transition was observed from a homogeneous structure in youth to one that contained fibers in middle-age, which degenerated and were associated with significant liquefaction in old age. In the diabetic child, the vitreous structure contained prominent fibers whose appearance was similar to middle-aged normals and not the age-matched controls. This study characterizes the morphological manifestations of precocious senescence of vitreous in a patient with diabetes. The abnormal vitreous fibers are likely the result of biochemical changes in collagen that are related to hyperglycemia--a phenomenon that could be inhibited by drug therapy.