In the passage of nutrient material from the blood to the lens two barriers must be traversed, namely, the ciliary processes (blood-aqueous barrier) and the lenticular capsule (aqueous-lens barrier). The same two barriers in reverse order oppose the removal of waste products of lens metabolism. Concentration gradients exist across each of these barriers, gradients that change continuously. Thus, there is operative at all times a dynamic equilibrium of osmotic forces between the lens and the aqueous on the one hand and between the aqueous and the blood on the other. Not only is there a continuous interchange of blood and waste products, but there is a simultaneous and delicately balanced alteration of the water content. For example, a meal rich in carbohydrates is ingested, which increases the dextrose content of the blood. Since the concentration of dextrose in the blood is then higher than that in the aqueous, a higher
BELLOWS JG, CHINN H. BIOCHEMISTRY OF THE LENS: XIII. PRODUCTION OF LENS OPACITIES BY INJECTION OF HYPERTONIC SOLUTIONS. Arch Ophthalmol. 1941;25(5):796–810. doi:10.1001/archopht.1941.00870110048004
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