MANY ATTEMPTS have been made to explain how the concentration of ascorbic acid in the aqueous humor is maintained in excess of that in the blood.1 Three different mechanisms have been proposed: (1) Ascorbic acid is synthesized by the lens *; (2) ascorbic acid is transported across the ciliary epithelial border in the oxidized state (i. e., as dehydroascorbic acid), where it is reduced to ascorbic acid by the lens †; (3) ascorbic acid is selectively concentrated by the ciliary epithelium, whence it diffuses to the posterior chamber.7‡
The chief evidence in support of the theories that associate the lens with the maintenance of relatively high concentrations of ascorbic acid in the aqueous humor is the observation that the concentration of the acid is less than normal when the lens is cataractous or absent. For instance, reduced concentrations of ascorbic acid in the aqueous humor have been observed
PURCELL EF, LERNER LH, KINSEY VE. ASCORBIC ACID IN AQUEOUS HUMOR AND SERUM OF PATIENTS WITH AND WITHOUT CATARACT: Physiologic Significance of Relative Concentrations. AMA Arch Ophthalmol. 1954;51(1):1–6. doi:10.1001/archopht.1954.00920040003001
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