In antiquity the aqueous humor was seen as essential to moisten and nourish the lens- the actual organ of vision-and therefore any loss was believed to lead to blindness. The recuperation of the eye after some aqueous loss during cataract couching and experimental loss in animals slowly undermined this idea in the 16(th) and 17(th) centuries. In the 18(th) century production of aqueous from the ciliary region and its outflow from the anterior chamber, and thus its circulation, was generally accepted. Early in the 19(th) century the aqueous was thought to be encapsulated, but by the end of the century the general dynamic principles of aqueous flow as we know them today were experimentally and clinically confirmed. The controversy concerning its mode of production and circulation that took place early in the 20(th) century was resolved with the discovery of the aqueous veins and advances in molecular biology.