It is generally assumed that in cats as in rabbits and man, the aqueous is drained into small episcleral and conjunctival vessels and that the pressure in these vessels is therefore the pressure counteracting the flow of aqueous from the anterior chamber.
In man and in rabbits this assumption is supported by the finding of aqueous veins in the episclera and conjunctiva,1,2,9,12 but in cats no such vessels seem to have been observed.
In all the 3 species there are intrascleral venous plexuses in the limbus region. In man, Ascher2 supposed that the aqueous from the canal of Schlemm found its way through the intrascleral venous plexus, where part of the aqueous became mixed with the blood. In rabbits, Troncoso15 described veins within the plexus which were separated from the anterior chamber only by the trabecular meshwork and were supposed to participate in the drainage of aqueous.
BILL A. Aspects of the Drainage of Aqueous Humor in Cats. Arch Ophthalmol. 1962;67(2):148-155. doi:10.1001/archopht.1962.00960020150008