THE CURRENT explanation of the reduction of intraocular tension by miotics in general may be summarized as follows:
Contraction of the pupil and the ciliary muscle, pulling on the scleral spur, widens the chamber angle and facilitates the escape of fluid into Schlemm's canal.
Dilatation of the smaller blood vessels to a various degree promotes absorption of fluid through the choroidal venous plexus, while the arterial supply of the ciliary body is thought to be reduced by compression of the smaller arteries in that area, due to the contraction of the ciliary muscle.
There seems to be little doubt as to the first point. The second part of the explanation is still hypothetic. The existence of this combined mechanism of compressing the arteries and dilating the veins has, to my knowledge, never been proved. The idea was advanced mainly to explain the reduction of intraocular tension by miotics, even if,
STOCKER FW. CLINICAL EXPERIMENTS WITH NEW WAYS OF INFLUENCING THE INTRAOCULAR TENSIONII. Use of Rutin to Enhance the Tension-Reducing Effect of Miotics by Reducing the Permeability of the Blood-Aqueous Barrier1. Arch Ophthalmol. 1949;41(4):429-435. doi:10.1001/archopht.1949.00900040439004