Fig. 3. Age-related changes in human vitreous collagen levels. Collagen content (mg; right ordinate) is indicated by solid dots (means) and darkly hatched boxes in the upper portion of the graph (height = standard error). Collagen concentration (mg/mL; left ordinate) is indicated by asterisks (means) and lightly hatched boxes in the lower portion of the graph (height = standard error). Vitreous collagen concentration decreases during the first decade of life because there is no net synthesis of collagen during this period of active growth of the eye. There are no significant changes in collagen content following age 20, consistent with the lifelong “stability” of this molecule. However, collagen concentration in the gel vitreous increases after ages 40 to 50. This is due to the decrease in gel vitreous that occurs during this time (see Fig. 2), concentrating the remaining collagen in an ever-decreasing volume of gel vitreous. The increase in gel vitreous collagen concentration between ages 50 to 60 and 80 to 90 is statistically significant (p < .05). (Balazs EA, Denlinger JL: Aging changes in the vitreous. In: Aging and Human Visual Function, pp 45–57. New York, Alan R. Liss, 1982.)