Normal visual function requires the shape of the globe to remain fixed and the optical pathway from the cornea to the retina to remain clear. This requires that the nutrition of the intraocular tissues in the optical pathway must occur with a minimum number of blood vessels. All of this is accomplished very efficiently by the production of the clear aqueous humor, its circulation into the anterior chamber, and its drainage from the anterior chamber angle through tissues with high resistance (trabecular meshwork and uvea). The intraocular pressure thus is maintained, the shape of the eye is preserved, the refracting surfaces are kept in place, and the avascular cornea and lens are provided with nourishment and waste removal.