Vascular changes that occur during the phasic variations of tension in chronic glaucoma.

Abstract

IT is abundantly clear that some relationship exists between ocular tension on the one hand and the state of the perilimbal episcleral vessels on the other. The ciliary congestion associated with acute and sub-acute attacks of congestive glaucoma, and the dilatation of the larger vessels of this region in absolute glaucoma, have long been recognized as examples of this relationship. Furthermore, the importance of these vessels in the drainage of aqueous from the anterior chamber has, by gradual stages, been established. The anatomical researches of Schlemm (1831), Rouget (1856), Leber (1873), Maggiore (1917) and Dvorak-Theobald (1934), have provided us with the basis of our knowledge of the vascular connections in the neighbourhood of the angle of the anterior chamber. More recently, the discovery of the aqueous veins by Ascher (1942) and Goldmann (1946), and the tracing of these to the canal of Schlemm by Ashton (1951), have confirmed a direct continuity between the anterior chamber and the vessels visible on the surface of the globe. The more obvious changes in the episcleral vessels which follow gross changes in intra-ocular pressure have led to the inquiry whether there are also variations in the circulation on the surface of the globe in the less dramatic diurnal rise and fall of pressure which occurs in chronic glaucoma. The most detailed work on this subject is that of Thomassen (1947), who measured the pressures in episcleral vessels during these variations in tension. His method involved the direct compression of the vessel walls by a small transparent viewing chamber applied to the conjunctiva. He found that a rise in intra-ocular pressure was preceded by a rise in the pressure of the episcleral veins, and that a fall in the venous pressure initiated a fall in intra-ocular pressure. The pressure in the anterior ciliary arteries on the other hand did not vary with the changes in ocular tension.