e, 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, the bimodal occurrence was at age 45-49 years and age 65-69 years. Both peaks incidences in men were 5 years later than in women.
Tellez et al, in another small study consisting of 155 patients who were newly diagnosed with Graves ophthalmopathy, 26% were male and 36% were female; however, the prevalence was higher in the Europeans, at a rate of 42% versus 7.7% in Asians. Analysis of the data indicated that Europeans were 6.4 times more likely to have Graves ophthalmopathy than Asians.
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.
A difference of more than 2 mm between the 2 eyes of any given patient is considered abnormal.
Epstein et al state that proptosis is a globe that protrudes 18 mm or less and exophthalmos is protrusion of greater than 18 mm. The upper limit of normal was 21 mm.
In adult white males, the average distance of globe protrusion is 16.5 mm, with the upper limit of normal at 21.7 mm.
In adult African American ma