Orbital Decompression
Michael Richard, MD
DISEASE DESCRIPTION
Thyroid eye disease causes a lymphocytic infiltration of orbital muscle and fat with resultant expansion of these tissues from edema and deposition of hyaluronic acid and other glycosaminoglycans. The closed space of the bony orbit limits the expansion of the orbital contents, leading to the development of proptosis (Figure 32.1). Orbital decompression is performed to increase the intraorbital space by allowing the orbital contents to herniate into the adjacent ethmoid sinuses, maxillary sinus, and temporalis fossa (Figure 32.2). The amount of decompression is dependent on the specific indications of the patient — the amount of proptosis, the degree of orbital congestion, the nature of the orbital fat, and the presence of optic neuropathy.
Either one, two, or three walls are decompressed. Single-wall decompressions are less common but usually address the orbital floor. Classically, two-wall decompressions address the medial wall and the orbital floor, whereas three-wall decompressions include the lateral wall, although the procedure can be tailored to include any combination of orbital walls depending on the patient’s needs (Figure 32.3).
MANAGEMENT OPTIONS
Teprotumumab, a human monoclonal antibody against the insulin-like growth factor-1 (IGF-1) receptor, was approved in January 2020 by the U.S. Food and Drug Administration (FDA) for the treatment of thyroid eye disease. It is administered as a series of eight infusions given every 3 weeks. It has been shown in two studies to reduce proptosis by at least 2 mm in 71% and 83% of patients, respectively, during the active phase of the disease. This is likely to become a mainstay of management for proptosis. Although it is too early to say definitively, this treatment has the potential to greatly decrease the number of future orbital decompressions that will need to be performed.
Patients with moderate degrees of proptosis who are unwilling to undergo orbital surgery may consider repair of lid retraction only, to camouflage the amount of proptosis and improve ocular surface disease.
 FIGURE 32.1. Expansion of the orbital contents within the closed space of the bony orbit leads to proptosis. |
INDICATIONS FOR SURGERY
Elective procedure for proptosis-associated impaired cosmesis, lid retraction, or ocular surface dysfunction once the disease process has entered the quiescent phase
Emergent procedure in the active phase of disease for vision-threatening compressive optic neuropathy or corneal decompensation. Optic neuropathy cases require full decompression of the orbital apex at the area of the optic canal along the deep medial wall and apical floor.
Patients with thyroid eye disease often require some combination of orbital decompression, strabismus surgery, and eyelid surgery for rehabilitation once they enter the quiet phase of the disease process. These surgeries are performed in a stepwise manner beginning with orbital decompression, followed by strabismus surgery, and, finally, any lid repairs. The rationale for this sequence is that orbital decompression may affect diplopia and lid position (diplopia may improve or worsen following orbital decompression surgery and lid retraction may lessen following decompression). Similarly, strabismus surgery may affect lid retraction (recession of the inferior rectus can worsen lower lid retraction). Lid surgery, however, will have no effect on proptosis or strabismus.
 FIGURE 32.2. Illustration showing the bones that are commonly removed during orbital decompression surgery. |
 FIGURE 32.3. Anterior view of the left bony orbit. The three commonly decompressed walls are identified: the medial wall (A), the medial orbital floor (B) separated by the infraorbital canal from the lateral orbital floor (C), the anterolateral wall (D), and the posterolateral wall (E). Note that the junction between the medial wall and the medial floor is not marked for decompression, corresponding to the orbital strut, which is commonly preserved to prevent postoperative hypoglobus and diplopia. |
The amount of decompression achieved is well correlated with the degree of myopathy and the nature of the orbital fat. Generally, patients with more severe myopathy tend to have more fibrosis, which limits the amount of expansion of the orbital contents after bony decompression. This results in poorer decompressive results. Such patients should be counseled regarding this possibility, and a more aggressive decompression may be considered.
SURGICAL DESCRIPTION
Three-Wall Orbital Decompression
We use a swinging eyelid transconjunctival approach for the inferior and lateral walls and a transcaruncular approach for exposure to the medial wall.
Preoperative computed tomography (CT) is necessary to adequately evaluate the orbital landmarks and plan for the optimal surgical technique. There can be moderate degrees of variability in bony orbital anatomy that affect surgical planning. For example, CT will indicate how much of the lateral floor overlies the maxillary sinus, which will inform the surgeon as to how much decompression can be achieved in this area. It will also demonstrate the exact course of the infraorbital nerve, the location of the cribriform plate, and the position of the posterior wall of the maxillary sinus.
Swinging Eyelid Transconjunctival Approach
After induction of general anesthesia, infiltrate the lower eyelid and lateral canthal region with 1% lidocaine with 1:100,000 epinephrine using a ½-in 30-gauge needle. The lower eyelid is approached from the conjunctival side and the needle is advanced to the arcus marginalis and anesthetic is injected while the needle is withdrawn to ensure that there is a small bolus subconjunctivally. A small amount of anesthetic is injected into each of the three fat compartments in this manner.
Place a scleral protector on the eye beneath the lids.
Perform a lateral canthotomy and inferior cantholysis. Clamp the lateral canthus with a small curved hemostat. Use Westcott scissors to cut across the clamped area down to the lateral orbital rim. Rotate the scissors inferiorly to strum the inferior crus of the lateral canthal tendon. Cut and release the inferior crus entirely.
Using a #15 blade, make a transconjunctival incision approximately 5 mm inferior to the inferior border of the tarsal plate for the length of the eyelid. This incision should extend through the conjunctiva and lower lid retractors.
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