Fig. 4. Age-related changes in human vitreous hyaluronic acid (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. A. HA concentration in the gel vitreous. There is a fourfold increase in the concentration of HA during the first two decades of life. Considering that this is also a period of active growth of the eye and substantial increase in vitreous volume, there must be prolific synthesis of HA to increase concentrations so dramatically. After age 20, HA concentrations in the gel vitreous are stable. Since this is a period of decreasing amounts of gel vitreous (see Fig. 2), there must be a net decrease in the HA content of the gel to result in no substantial changes in concentration. B. HA concentration in the liquid vitreous. There are no data for the first 4 years since there is no liquid vitreous during this time. From the ages of 5 to 50 to 60 there is a 50% increase in the concentration of HA in the liquid vitreous. After this time, there is a substantial increase in liquid vitreous HA concentration. The magnitude of this accumulation of HA in the liquid component of the vitreous is even greater when one considers that this occurs during the time when the volume of liquid vitreous is increasing by twofold (see Fig. 2). (Balazs EA, Denlinger JL: Aging changes in the vitreous. In: Aging and Human Visual Function, pp 45–57. New York, Alan R. Liss, 1982.)