Exophthalmos 

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.^[1] 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.

The etiological basis of proptosis can be inflammatory, vascular, or infectious. In adults, thyroid orbitopathy is the most common cause of unilateral and bilateral exophthalmos. Other causes include such neoplasms as cavernous hemangiomas, lymphangiomas, lymphomas, Wegener granulomatosis, and orbital cellulitis.

In children, unilateral proptosis is often due to an orbital cellulitis–type picture, and, in bilateral cases, neuroblastoma and leukemia are more likely.

For instance, lymphangiomas, by their histologic nature, can increase in size during viral illnesses and result in an increase in orbital volume. A ruptured lymph hemangioma can enlarge due to 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.

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. 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.^[2] 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 at its anterior aspect, the orbital contents are displaced anteriorly, resulting in proptosis and exophthalmos.

Mortality/Morbidity

Proptosis due to any cause can compromise visual function and the integrity of the eye.

• A proptotic eye not adequately protected by the lids, as with lagophthalmos, can develop exposure punctuate keratopathy. Such disruption of the finely orchestrated homeostatic mechanism to protect the eye will result in corneal compromise, epithelial death, ulceration, and possible corneal perforation in severe cases. At a minimum, the disruption of the tear film layer and incomplete moisturizing of the eye will adversely affect vision and ocular comfort.
• Proptosis secondary to a space-occupying process can result in a compressive optic neuropathy. Impeded optic nerve blood flow results in irreversible neuronal death and diminished optic nerve function. Such manifestations as depression of visual and color acuities, pupillary dysfunction, and constriction of visual field can occur.
• Proptotic compressive effects are remedied initially by forward protrusion of the eye, thereby reducing the compressive effect within the orbit. However, the eye can extend only so far, and severe stretching can adversely affect the eye and compromise the optic nerve.

Race

• In adult Caucasian males, the average distance of globe protrusion is 21 mm, and, in adult African American males, it is 23 mm.
• Females also show racial variation. A difference of more than 2 mm between the 2 eyes of any given patient is considered abnormal.

Sex

Thyroid orbitopathy has a female preponderance with a female-to-male ratio of 5:1.

Age

Proptosis occurs in both adults and children at any age. Thyroid orbitopathy and the resultant exophthalmos show a predilection for females aged 30-50 years.