Fig. 8. Age-related changes in human vitreous hyaluronan (HA) concentration. The dots represent the means of the samples. The vertical height of the boxes represents the standard error of the means. The horizontal width of the boxes represents the age ranges in the sample group. Between the ages of 5 and 10 years, the HA concentration is about the same (0.1 mg/mL) in both gel and liquid vitreous. A: Concentration of HA in gel vitreous. There is a fourfold increase in the concentration of HA during the first three decades of life. Considering that this is also a period of active growth of the eye and substantial increase in vitreous volume, there must necessarily be prolific synthesis of HA to increase concentration so dramatically. After the age of 20 years, HA concentrations in the gel vitreous are stable. Because this is a period of decreasing amounts of gel vitreous, there must be a net decrease in the HA content of the gel to result in no substantial changes in concentration. B: Concentration of HA in liquid vitreous. There are no data points for the first 4 years because there is no measurable liquid vitreous during this time. From the ages of 5 to 50 or 60 years, there is a 50% increase in the concentration of HA in liquid vitreous. Thereafter, the HA concentration in liquid vitreous increases substantially. The magnitude of this HA accumulation in the liquid compartment of the corpus vitreum is even more impressive considering that this increase in HA concentration occurs during a time when the volume of liquid vitreous increases twofold. (From Balazs EA, Denlinger JL. Aging changes in the vitreous. In Aging and Human Visual Function. New York: Alan R. Liss, 1982:45, with permission)