Page:A manual and atlas of medical ophthalmoscopy.djvu/151

Rh the tumour than optic neuritis, and it is not uncommon for sight, damaged much or little by the neuritic process, to fail rapidly at a subsequent period from secondary pressure effects.

Associated Changes.—A cysticercus has been occasionally observed in the vitreous humour, but the coincidence of one there with the symptoms of cerebral tumour due to another in the brain, has not, I believe, hitherto been recorded.

Consecutive Changes.—Optic neuritis is frequent in hydatid cysts, having all the characters of the neuritis which occurs in growths—swollen papilla, obscured and tortuous vessels, hæmorrhages. It has been observed with hydatid cyst of both cerebrum and cerebellum. It may go on to consecutive atrophy, life being prolonged for years. The few cases on record of neuritis associated with cysts in the brain, the nature of which was not ascertained, were probably examples of hydatid disease.

Miliary aneurisms have been spoken of in connection with cerebral hæmorrhage. Intra-cranial aneurisms of larger size are not, as a rule, accompanied by any associated ocular changes: those of the central artery of the retina being too rare to be of significance. Nor do they often cause consecutive changes, except their position is such as to press upon the optic nerve (causing unilateral amaurosis and secondary atrophy), on the chiasm a (bilateral atrophy), or, very rarely, on the optic tract (causing hemiopia). An aneurism of the internal carotid may obstruct the cavernous sinus, and cause transient fulness of the retinal veins without papillary changes. Commonly the pressure is relieved by the free communication of the ophthalmic, and facial veins, and the enlarged angular vein may be conspicuous beneath the skin. In rare cases, however, an aneurism in this situation has led to optic neuritis, as in a case recorded by Michel, in which double neuritis, with evidence