Pressure in the canal of Schlemm.

THE pressure relationships in the anterior chamber, the canal of Schlemm, and the episcleral venous plexus are of obvious importance to the understanding of the drainage of aqueous humour. Episcleral venous pressures have been estimated by several workers (Thomassen, 1947 ; Linner, 1954 ; Bain, 1954), but so far no direct measurements of the pressure in the canal of Schlemm have been attempted. The only comparable measurement in the literature is that of Duke-Elder (1926) who measured the pressure in the veins of the circle of Hovius in the dog and found the pressure to be slightly higher than the intra-ocular pressure. It was, therefore, considered worthwhile to attempt direct measurement of the pressure relationships of the canal of Schlemm and the anterior chamber in the eye of the living Rhesus monkey, in which the anatomical arrangements are very simnilar to those found in man.