The vascular responses of the eye

Abstract

The investigations described in this paper follow from the theory sponsored by one of us, that the aqueous humour is a dialysate of the blood and the vitreous body is a simple hydrophilic gel (1927, a and 1930). During the past four years a series of papers has been published defining the conditions governing the maintenance and control of the intra-ocular pressure in the normal eye (1927, b , 1929, 1931); the present paper is an attempt to carry these investigations from the physiological to the pathological aspects of the subject. From our physiological work there emerges the hypothesis that pathological variations in the intra-ocular pressure may depend on two mechanisms: the one involving a vascular upset, and the other dependent upon physico-chemical changes in the vitreous body—and the clinical picture presented by glaucoma exhibits much that is confirmatory to this view. It is with the first of these possibilities that we are immediately concerned. In considering the possible causes of a vascular disturbance in the eye such as could be responsible for a rise (especially an acute rise) in the intra-ocular pressure, it appeared to us that a fruitful speculation might lie in the activity of a substance corresponding to the H-substance which has been demonstrated by Lewis (1927) and his co-workers to have so widespread and potent effects upon the vascular responses of the skin. By experiments on the intact dog and by the perfusion of the surviving head (Colle, Duke-Elder and Duke-Elder, 1931) we have already shown that histamine has an effect on the vessels of the eye similar to that already determined by Burn and Dale (1926) in the limbs; a dilatation of the minute vessels is associated with a constriction of the more central parts of the vascular tree ; when the minute vessels have lost their tone the latter effect predominates, but in a normal state of tonicity the injection of histamine into the circulating blood is associated with a macro-scopically visible vaso-dilatation of the capillaries of the inner eye, an increase in the permeability of the capillary walls allowing an excess of colloids to appear in the aqueous humour, and with a marked rise in the intra-ocular pressure. If a substance of this nature were produced pathologically in the eye, we have to hand all the materials necessary to inaugurate an acute rise of tension.