34 Orbital Decompression: Floor and Medial Wall Via an External Approach
Surgical orbital decompression is indicated for patients with compressive optic neuropathy, exposure keratopathy, globe luxation, uncontrolled elevation of intraocular pressure, or disfiguring proptosis secondary to thyroid eye disease. Multiple different techniques have been described to achieve effective orbital decompression. However, there is still controversy regarding the best surgical option likely to the variability in patient condition, patient anatomy, surgeon training, and available instrumentation.
The transconjunctival (for the floor) and transcaruncular approaches (for the medial wall) to the orbit are minimally invasive, provide excellent exposure, and leave minimally visible incisions.
34.1 Key Principles
The transconjunctival decompression provides a wide exposure of the orbital floor, most of which is removed to allow expansion of the orbital fat into the maxillary sinus. During the floor removal, care needs to be taken with the inferior-orbital neurovascular bundle (V2) to avoid deep bleeding and paresthesia/hypoesthesia of the cheek.
Preservation of the orbital strut while removing bone decreases the incidence of new-onset diplopia secondary to a hypoglobus.
The transcaruncular approach provides excellent exposure of the medial wall in a minimally invasive manner. Through this route, the orbital apex can be widely decompressed to improve visual acuity in patients with compressive optic neuropathy. 1 , 2
Excellent visualization of the orbit is imperative for effective decompression and avoidance of complications. Conjunctival incisions should be made large enough for proper retraction of the orbital structures. Maintaining orbital fat behind dissection planes (e.g., periorbital or orbital septum) and retractor instruments assists in this visualization.
The main aim of orbital decompression is to expand the orbital cavity to allow the orbital contents (eye, muscles, fat, nerves, and vessels) to herniate into the paranasal sinuses. This serves to reduce proptosis, alleviate exposure keratopathy, relieve compressive optic neuropathy, and provide better cosmesis to the patients.
Through the transcaruncular and transconjunctival approaches, these structures can be displaced into the ethmoidal and maxillary sinuses, respectively.
Via the conjunctiva, a skin incision is avoided. With careful dissection, the inferior orbital septum can be preserved, greatly reducing the risk of developing secondary lower eyelid retraction.
Patients with compressive optic neuropathy need to have the orbital apex decompressed, which is well achieved through a transcaruncular dissection to remove the medial wall in the posterior-most aspect.
Advantages over other techniques include no external visible scar, less damage to adjacent tissue, and wide exposure to the entire medial and inferior orbital walls.
Following surgery, proptosis may be reduced from 3 to 7 mm. By reducing proptosis, patients should experience improvement in symptoms associated with corneal exposure, such as foreign body sensation, tearing, and blurred vision. Also, a considerable reduction in vascular congestion of the periocular tissues is usually perceived (Fig. 34‑1). 1 , 2 , 3 , 4 , 5 , 6
Orbital decompression is indicated in patients with
Moderate to severe exophthalmos.
Uncontrollable intraocular hypertension.
Compressive optic neuropathy.
Unacceptable cosmetic appearance.
Patients with mild exophthalmos (2–3 mm) are good candidates for a floor decompression alone. But when patients have severe visual loss due to optic nerve compression, a wide decompression of the posterior ethmoidal cells is mandatory, and in our experience, this can be best achieved through a transcaruncular approach.
Patients with active sinus infection need to be treated with antibiotics and/or antifungal medications before the orbital walls are disrupted. Also, if there is no severe visual loss that requires an urgent decompression, it is always preferred to perform surgery when the thyroid eye disease is in the inactive phase. Orbital decompression is also contraindicated in patients with an open globe or with a retinal detachment.
34.7 Preoperative Preparation
As with all orbital surgery, patients need to have a complete systemic and ophthalmic examination.
Unless decompression is urgent for vision salvage, the thyroid disease should be controlled and stable for 6 months prior to the surgery.
Patients should stop smoking at least 4 to 6 months prior to the surgery.
All patients need to have a CT scan with fine axial and coronal sections of the orbits to confirm that the sinuses are clear and to locate the position and height of the lamina cribrosa.
In our personal experience, 50 to 80 mg of oral prednisolone, 2 to 3 days before the procedure, helps reduce postsurgical inflammatory edema.
It is mandatory that patients stop aspirin or anticoagulant medication days before the procedure, as with any other major surgery. This suspension of medication should be approved and ordered by the patient’s primary care physician, cardiologist, or prescribing physician.
It is important to preserve the lamina cribrosa to avoid cerebrospinal fluid leak.
Prophylactic antibiotic is not standardized, and we do not routinely prescribe antibiotics prior to an orbital decompression surgery.
34.8 Operative Technique
Patients undergoing a transconjunctival and transcaruncular decompression are operated under general anesthesia.
34.8.1 For the Transconjunctival Approach Decompression
After infiltration of the lower eyelid in the subconjunctival space at the inferior fornix using 1% lidocaine with epinephrine 1:100,000, a 6–0 silk suture is passed in the lower eyelid margin just in front of the grey line, to allow the lower eyelid to be everted over a Desmarres retractor. Using a scalpel or a monopolar cautery, an incision is made inferiorly to the tarsal plate (Fig. 34‑2). Dissection is carried out through the lower eyelid retractors to the orbital rim in the preseptal plane to avoid fat herniation which may make visualization difficult (Fig. 34‑3). This is aided by the use of a malleable retractor to displace the globe and orbital tissues. Once the orbital rim is exposed, the periosteum is incised with electrocautery across the entire inferior rim (Fig. 34‑4). The periosteum is elevated with a periosteal elevator to gain access to the subperiosteal space of the orbital floor (Fig. 34‑5). After good exposure of the floor, using a periosteal elevator or a hemostatic clamp, a small opening in the bone is created medial to the infraorbital neurovascular bundle. With rongeurs, the bony decompression is enlarged in all directions (Fig. 34‑6). Care should be taken not to damage the infraorbital neurovascular bundle. It is preferred to leave the “orbital strut” (the junction of the maxillary and the ethmoidal sinuses) intact to reduce inferomedial displacement of the globe, hypoglobus, and postoperative diplopia. The periorbita needs to be incised to allow the orbital contents to herniate through the bone defect. The conjunctiva is typically closed with one buried 7–0 polyglactin suture in the central location.