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Orbital Surgery


Key Points

  • 1.

    Endoscopic sinus surgical techniques have advanced to include the treatment of select orbital pathology due to the close proximity of the orbit to the paranasal sinuses, advances in surgical instrumentation, and a working relationship with ophthalmologists.

  • 2.

    Endoscopic approaches to the orbit require a deep knowledge and an accurate intraoperative identification of orbital anatomy.

  • 3.

    Excess tearing (epiphora) can result from hypersecretion or failure of drainage (nasolacrimal system obstruction). Endoscopic dacryocystorhinostomy (DCR) is the preferred treatment for nasolacrimal duct obstruction.

  • 4.

    Thyroid eye disease (TED) is the most common extrathyroidal manifestation of Graves’ disease and is the leading cause of proptosis in adults. Endoscopic orbital decompression is often an important treatment approach to these patients.

  • 5.

    Traumatic optic neuropathy is categorized as direct or indirect, and surgical intervention appears to be of limited benefit.

Pearls

  • 1.

    Thyroid eye disease results from autoimmune inflammation of muscle and fat, where the thyroid-stimulating hormone (TSH) receptor is the autoantigen.

  • 2.

    Dacryocystorhinostomy is an effective surgical management for nasolacrimal duct obstruction.

  • 3.

    The medial rectus, superior rectus, inferior rectus, and inferior oblique muscles are innervated by cranial nerve III. The superior oblique muscle is innervated by cranial nerve IV. The lateral rectus muscle is innervated by cranial nerve VI.

  • 4.

    The anterior and posterior ethmoid arteries are distal branches of the internal carotid circulation.

Questions

1

Describe the important bony anatomy of the orbit.

The orbit is a pyramidal shaped space that is made up of seven bones: ethmoid, frontal, lacrimal, maxillary, palatine, sphenoid, and zygomatic ( Fig. 31.1 ). The medial walls of each orbit lie parallel to each other and the lateral walls lie 45 degrees to the ipsilateral medial wall and 90 degrees to the contralateral lateral wall. The orbital walls are lined by periosteum called periorbita.

Fig. 31.1, Bony anatomy of the orbit.

2

Which bones make up each wall of the orbit?

The roof of the orbit is made up of the frontal bone and lesser wing of the sphenoid. The floor of the orbit is composed of the maxillary, palatine, and zygomatic bones. The medial wall of the orbit is composed of the ethmoid, lacrimal, maxillary, and sphenoid bones. The lateral wall of the orbit is composed of the greater wing of the sphenoid and the zygomatic bone.

3

What are the dimensions of the orbit in adults?

The pyramidal shaped orbit has a typical volume of 30 mL. The entrance height is 35 millimeters and the entrance width is 40 millimeters. The width of the orbit is greatest 1-centimeter posterior to the entrance of the orbit, which corresponds to the equator of the globe. The medial wall length is 45 mm.

4

What are the orbital foramina and which structures are contained within them?

The optic foramen passes through the lesser wing of the sphenoid extending from the middle cranial fossa to the orbital apex and contains the optic nerve, ophthalmic artery, and sympathetic fibers from the carotid plexus. The supraorbital foramen is located at the medial third of the superior margin of the orbital rim and contains the supraorbital nerve, artery, and vein. The anterior ethmoidal foramen is located at the frontoethmoidal suture 24 millimeters posterior to the orbital rim and contains the anterior ethmoidal vessels and nerve. The posterior ethmoidal foramen is located 12 millimeters posterior to the anterior ethmoidal foramen at the junction of the medial wall and orbital roof and contains the posterior ethmoidal vessels and nerve. The 24/12/6 rule is a nice reference to help remember foramina locations in the orbit, which stands for anterior ethmoid artery (24 millimeters), posterior ethmoid artery (12 millimeters), and optic nerve (6 millimeters) in sequential measurements from the posterior lacrimal crest. The zygomaticotemporal and zygomaticofacial foramina are located within the lateral wall of the orbit and transmit branches of the zygomatic nerve and artery.

5

What are the orbital fissures and which structures are contained within them?

The superior orbital fissure is 22 millimeters in length and lies inferior and lateral to the optic foramen. It is formed by the greater and lesser wing of the sphenoid and is divided into superior and inferior parts by the lateral rectus. The superior part contains the frontal and lacrimal branches of cranial nerve V1 and cranial nerve IV. The inferior part contains the superior and inferior divisions of cranial nerve III, the nasociliary branch of V1, cranial nerve VI, the superior ophthalmic vein, and the sympathetic nerve plexus. The inferior orbital fissure lies between the lateral wall and orbital floor (runs deep to the orbital floor) and contains branches of cranial nerve V2 and the inferior ophthalmic vein ( Fig. 31.2 ).

Fig. 31.2, Anterior view of the orbit on a dry skull. Foramina, or openings in the bone, can be seen. The superior orbital fissure is found at the orbital apex. The inferior orbital fissure is found on the orbital floor. The optic foramen is found on the superior-medial wall.

6

What are the extraocular muscles and where are they located?

There are six extraocular muscles within each orbit ( Fig. 31.3 ) that control movement of the globe: inferior rectus, lateral rectus, medial rectus, superior rectus, superior oblique, and inferior oblique. With the inferior oblique as the exception, all extraocular muscles originate at the orbital apex. The four rectus muscles originate from the annulus of Zinn (a tendinous ring that encircles the inferior portion of the superior orbital fissure and optic foramen) and insert onto the anterior portion of the globe. The superior oblique travels from the orbital apex to the trochlea and makes a sharp turn (54 degrees) to insert on the globe. The inferior oblique travels from a shallow depression in the orbital plate of the maxillary bone, inferior to the lacrimal fossa, posteriorly laterally and superiorly to insert on the globe.

Fig. 31.3, Schematic diagrams depicting the extraocular muscles from lateral (A) and cut anterior (B) views. SO, superior oblique; IO, inferior oblique; MR, medial rectus; LR, lateral rectus; SR, superior rectus; IR, inferior rectus. In the lateral view (A) , the muscles are depicted attached to the common tendon.

7

Describe the innervation of the extraocular muscles.

The inferior rectus, medial rectus, superior rectus, and inferior oblique muscles are innervated by cranial nerve III. The superior oblique muscle is innervated by cranial nerve IV. The lateral rectus muscle is innervated by cranial nerve VI. The blood supply to the extraocular muscles is provided by the inferior and superior muscular branches of the ophthalmic artery, lacrimal artery, and infraorbital artery.

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