Exophthalmos is defined in Dorland's Medical Dictionary as an "abnormal protrusion of the eyeball; also labeled as proptosis." Proptosis in the same reference is defined as exophthalmos.
Henderson reserves the use of the word exophthalmos for those cases of proptosis secondary to endocrinological dysfunction. Therefore, this dictum will be followed, and non–endocrine-mediated globe protrusion will be referred to as proptosis and exophthalmos will be reserved for protrusion secondary to endocrinopathies. See the image below.
Bilateral exophthalmos and upper lid retraction secondary to Graves disease.
The etiological basis of proptosis can include inflammatory, vascular, infectious, cystic, neoplastic (both benign and malignant, metastatic disease), and traumatic factors. Some representative examples (not a complete list of proptosis from different causes) include infectious causations such as orbital cellulitis and subperiosteal abscesses. Traumatic causations could be orbital emphysema, retro-orbital hemorrhage, and carotid-cavernous fistula. Vascular causations not traumatically related would be orbital arteriovenous malformation (AVM) varices and aneurysms. Neoplastic causations include adenocarcinoma of the lacrimal gland, pleomorphic adenoma of the lacrimal gland, meningioma, lymphoma, and metastatic disease.
For instance, lymphangiomas, by their histologic nature, can increase in size during viral illnesses and result in an increase in orbital volume. A ruptured lymphangioma can enlarge after its rupture and sequestering of heme, which pathologically is described as a chocolate cyst. Orbital varices can result in proptosis with increased venous pressure in the orbit, as seen with a Valsalva maneuver or change in postural position.
In children, unilateral proptosis is often due to an orbital cellulitis–type picture, and, in bilateral cases, neuroblastoma and leukemia are more likely. Other causes in children include rhabdomyosarcoma, retinoblastoma, capillary hemangioma, dermoid cyst, glioma of the optic nerve, and metastatic disease.
Thyroid orbitopathy, also referred to as thyroid ophthalmopathy, is categorized as an inflammatory process. As it affects the orbit, the author prefers to use thyroid orbitopathy and, more particularly, thyroid-associated orbitopathy, commonly referred to as Graves disease. In adults, it is the most common cause of unilateral and bilateral exophthalmos.
The etiology of the thyroid-related orbitopathy is an autoimmune-mediated inflammatory process of the orbital tissues, predominantly affecting the fat and the extraocular muscles. Lymphocytes, plasma, and mast cells are the cellular constituents in this process. The deposition of glycosaminoglycans and the influx of water increase the orbital contents. Over time, fibrosis can occur.[2, 3] Genetic factors have been associated with Graves disease. Obstruction of the superior ophthalmic vein with resultant diminished venous outflow also contributes to the orbital engorgement.
Nunery has segregated patients with thyroid-related orbitopathy into type I and type II. Those with type I do not have restrictive myopathy, whereas those with type II do. Type I was believed to be caused by a profundity of hyaluronic acid manufactured by the orbital fibroblasts, stimulating lipoid hyperplasia and edema. Patients with type II experience restrictive myopathy and have diplopia within 20° of fixation.
Orbital emphysema can be a significant cause of proptosis and requires emergency treatment.
No matter what the etiology may be, globular protrusion is secondary to the increase in volume within the fixed bony orbital confines. Since the orbit is widest toward its anterior aspect, the orbital contents are displaced anteriorly, resulting in proptosis and exophthalmos.
Bartley et al had reported a frequency of 2.9 cases per 100,000 population per year in men and 16 cases per 100,000 population per year in women. They also observed a bimodal distribution in both sexes, with women showing one peak at age 40-44 years and the other peak at age 60-64 years. In men, 