Orbital disease usually arises within the orbit or by spread from adjacent structures, particularly the paranasal sinuses. The etiology may be inflammatory, due to infection; neoplastic, either benign or malignant and arising from bone, muscle, nerve, blood vessels, or connective tissue; or due to vascular anomalies, including arteriovenous malformations and arterial fistulas. Orbital lesions may also be due to metastatic tumors. Thus, orbital disease may be due to serious and sometimes life-threatening entities.
An increase in orbital contents results in displacement of the globe. Since the orbit has rigid bony walls except anteriorly (see Chapter 1), such displacement usually manifests predominantly as forward protrusion of the globe (proptosis), which is the hallmark of orbital disease. Swelling within the muscle cone displaces the globe directly anteriorly (axial proptosis), whereas swelling outside the muscle cone will also cause sideways or vertical displacement (non-axial proptosis).
Bilateral involvement generally indicates systemic disease, such as Graves' disease. The term “exophthalmos” is often used when describing proptosis associated with Graves' disease.
Pulsating proptosis may be due to carotid-cavernous fistula, arterial orbital vascular malformation, or transmission of cerebral pulsations due to a defect of the superior orbital roof, as in the sphenoid dysplasia of type 1 neurofibromatosis. Proptosis that increases on bending the head forward or with Valsalva's maneuver is a sign of venous orbital vascular malformation (orbital varices) or meningocele. Intermittent proptosis may be the result of a sinus mucocele. The Hertel exophthalmometer (see Chapter 2) is the standard method of quantifying the magnitude of proptosis. Serial measurements are most accurate if performed by the same individual with the same instrument. Pseudoproptosis is apparent proptosis in the absence of orbital disease. It may be due to high myopia, buphthalmos, or lid retraction.
Proptosis does not impair vision unless there are corneal changes due to exposure, but the orbital process itself, particularly if it arises from, involves, or compresses the optic nerve, or if it causes compression of the globe, resulting in distortion of the retina and possibly elevation of intraocular pressure, may impair vision. A relative afferent pupillary defect (RAPD) or impairment of color vision may identify optic nerve dysfunction before there is significant reduction of visual acuity.
Limitation of ocular movements resulting in diplopia (double vision) may be due to direct involvement of the extraocular muscles, interference with their mechanisms of action, or dysfunction of the oculomotor, trochlear, or abducens nerves. Pain may occur as a result of rapid expansion, inflammation, or infiltration of sensory nerves.
Disease involving the superior orbital fissure produces a characteristic combination of diplopia, resulting from disturbance of function of the oculomotor, trochlear, and abducens nerves, corneal and facial anesthesia (ophthalmic division of trigeminal nerve), and possibly proptosis, known as the superior orbital fissure syndrome. Lesions at the orbital apex also result in optic ...