EXOPHTHALMOS

also spelled Exophthalmus, also called Proptosis, abnormal protrusion of one or both eyeballs. The condition in most cases results from accumulation of fluid in the fatty tissues that cushion the eyeball in its socket, or orbit. The usual cause of this swelling of the orbital tissue is Graves' disease, a type of hyperthyroidism (oversecretion of thyroid hormone), but it may also follow the spread of infection from the paranasal sinuses or the teeth. Less common causes of exophthalmos include hemorrhage or aneurysm of the internal carotid artery and congenital glaucoma or severe myopia. True exophthalmos may be divided into simple and malignant forms. In both, edema (swelling) is frequent in the outer half of the upper lids, the lower lids, and adjacent areas. In simple exophthalmos, eye movements are not grossly abnormal, but lid lag may be present, and conjunctival involvement is minimal or absent. Visual acuity is normal, and there is no double vision. In malignant exophthalmos, the eyes are more prominent, the conjunctival swelling is marked, the eyes cannot be moved normally, and double vision is frequent; these various abnormalities are progressive; visual acuity becomes reduced, and the survival of the eyes is threatened.