Page:A manual and atlas of medical ophthalmoscopy.djvu/129



diseases of the brain, two forms of ophthalmoscopic change may he met with:—First, those which are a consequence of the general condition on which the cerebral disease remotely depends—associated changes; and, secondly, those which are the consequence of the cerebral disease—consecutive changes.

It has been supposed that the state of the circulation in the eye and brain correspond, and that the anaemia and hyperemia of the brain are revealed by similar conditions in the fundus oculi. But, as has been already said, such a statement, if true at all, is true only within certain narrow limits. The intra-ocular tension so regulates the state of the vessels of the eye, that very little alteration occurs in them, when changes occur in the condition of the vessels of the brain. The eyeball participates in variations in the blood-supply to the whole head, but it does not share simple vascular states of the brain (in which the rest of the head does not participate) to a degree which can render it a sensitive index of the existence of those states. This statement applies especially to the retinal vessels. The optic