Orbital Disorders

The ocular orbit is a cavity comprising complex anatomic relationships that surround the globe. Despite their advanced understanding of the eye itself, many optometrists struggle with the anatomy of the orbit from which orbital disease stems. This article reviews both the anatomic relationships among the globe, orbit, and adjacent structures and the pathophysiology of orbital disorders that take place beyond the globe.

ANATOMY REFRESHER

Walls and Bones

The orbit is a compartment bordered by four walls and formed by seven bones. The medial wall is in part formed by the lamina papyracea of the ethmoid bone, through which the anterior and posterior ethmoidal neurovascular bundles pass. The paper-thin quality of this bone, along with the neurovascular foramina, may provide a passageway for infection and inflammation to spread from the ethmoid sinuses, making them the most common sources of orbital cellulitis. The lateral wall, the strongest wall of the orbit, contains the zygomatic bone and greater wing of the sphenoid.

The orbital roof is formed by the frontal bone and lesser wing of the sphenoid, together making up a portion of the cranial vault’s floor. The orbital floor is composed of the maxillary, zygomatic, and palatine bones. It is commonly fractured in trauma, causing herniation of the orbital contents into the maxillary sinus.

Sinuses

Knowledge of the adjacent structures is integral in understanding orbital disease. The cavernous sinus is an important structure posteromedial to the orbit that is filled with blood from the superior and inferior ophthalmic veins and other tributaries. Key structures that run through the cavernous sinus include cranial nerves III, IV, V1, V2, and VI. For any disease process affecting multiple cranial nerves simultaneously, therefore, consider involvement of the cavernous sinus or orbital apex.

Other adjacent structures are the air-filled sinuses, which surround the orbit. These sinuses include the maxillary sinus inferior to the orbit, the ethmoid sinus medial to the orbit, the frontal sinus above the orbit, and the sphenoid sinus inferior to the cavernous sinus.

EVALUATING ORBITAL DISEASE

Most optometrists do not encounter orbital disease frequently in practice. However, we should be comfortable enough to take the next appropriate step in management. When we evaluate a patient for orbital disease, a systematic approach is helpful (see The Six P’s of Orbital Disease).

Trauma

Trauma to the orbital region may be the result of an altercation, a fall, a sports-related injury, or a motor vehicle accident. In patients with trauma, we should evaluate for evidence of an orbital fracture (Figure 1). Signs of a fracture may include diplopia, restricted eye movements, enophthalmos, orbital crepitus, or maxillary hypoesthesia due to infraorbital nerve damage. In the event of a suspected orbital fracture, an orbital CT without contrast should be obtained.

Not all fractures require repair, but patients with diplopia in primary gaze, diplopia lasting longer than 1 or 2 weeks, any evidence of entrapment, early enophthalmos, hypoglobus, and multi-bone or large fractures should be referred for further evaluation.¹

Although uncommon, a carotid-cavernous fistula may also be associated with orbital trauma. Signs include engorged conjunctival vessels to the limbus, elevated IOP, proptosis, restricted motilities, and engorged extraocular muscles.

Autoimmune-Related Disease

Thyroid-associated orbitopathy (TAO), also known as Graves orbitopathy or thyroid eye disease, is an autoimmune-related disease affecting 20% to 25% of patients with Graves hyperthyroidism.² It is often characterized by a rapid inflammatory phase resulting in diplopia, exophthalmos, lid retraction, exposure keratopathy, and, rarely, compressive optic neuropathy (Figure 2). The most important component of managing patients with TAO is ensuring control of their underlying thyroid dysfunction. Smoking cessation should be stressed, as it is the single most modifiable risk factor for development and progression of TAO.³

In patients with mild to moderate TAO, we may be managing exposure keratopathy and ensuant dry eye. In advanced TAO, it is important to rule out compressive optic neuropathy from severely enlarged extraocular muscles. Advanced TAO may require additional treatment such as intravenous or oral steroids, orbital decompression, and strabismus surgery.

Inflammation

For patients who present with rapid onset of significant eyelid edema in the absence of an underlying thyroid disorder, consider a diagnosis of preseptal cellulitis, orbital cellulitis, or orbital pseudotumor.

Preseptal cellulitis, by definition, consists of soft tissue edema anterior to the orbital septum (Figure 3). It may be associated with a hordeolum, dacryocysitis, or cutaneous break. Preseptal cellulitis should be managed with a short course of oral antibiotics and close follow-up.

Progression of preseptal cellulitis may lead to orbital cellulitis, which involves inflammation of the soft tissues behind the orbital septum. Signs of orbital cellulitis include diplopia, proptosis, chemosis, loss of vision, afferent pupillary defect, and often fever.⁴ Although preseptal cellulitis may progress to orbital cellulitis, orbital cellulitis is most commonly secondary to adjacent ethmoid sinusitis through the thin lamina papyracaea. Management of orbital cellulitis consists of hospital admission for intravenous antibiotics and close inpatient follow-up. Without immediate treatment of orbital cellulitis, progression into the cavernous sinus may occur, which is associated with high mortality.⁵

Orbital pseudotumor, also known as nonspecific orbital inflammation, can present in a nearly identical fashion to orbital cellulitis and should remain high on the differential. It can cause inflammation of numerous structures within the orbit (see Nonspecific Orbital Inflammation). Often, the inflammation starts at the lacrimal gland laterally, and on imaging there is minimal radiologic evidence of sinusitis (Figure 4). Management of orbital inflammation consists of an inflammatory and infectious workup to rule out alternative causes and often treatment with high-dose oral or intravenous steroids.

Benign and Malignant Lesions

When patients present with any number of orbital signs, such as restricted motilities and proptosis, we need to keep space-occupying lesions in our differential. These can range anywhere from benign entities such as cavernous hemangiomas to more malignant processes such as a metastasis to the extraocular muscles. Ultimately, diagnosis is made by a combination of orbital imaging and tissue biopsy.

DON’T FEAR THE ORBIT

Orbital disorders can be a difficult topic to master, but worthwhile. An organized and thorough approach is critical. Rapid assessment and appropriate management can lead to vision-saving—or life-saving—outcomes.