Optic Nerve Decompression
Ralph Metson
INTRODUCTION
The technique of optic nerve decompression is a natural extension of the more commonly performed endoscopic orbital decompression for treatment of Graves’ orbitopathy. In patients with visual loss caused by compressive optic neuropathy, removal of bone from the optic canal to relieve pressure along the nerve sheath can be a vision-saving operation.
HISTORY
Patients typically present with a progressive unilateral visual loss. Ophthalmologic evaluation confirms the presence of a compressive optic neuropathy. The cause of this neuropathy may be evident in patients with a known history of bony craniofacial dysplasia, sinonasal neoplasm, or Graves’ disease. In others, CT scan or MRI will typically reveal a lesion along the course of the optic nerve, most commonly in the orbital apex or lateral sphenoid sinus. Although optic nerve decompression was performed in the past for patients with traumatic injury to the optic nerve, high-dose steroids are now the treatment of choice for these individuals.
PHYSICAL EXAMINATION
Early findings of optic neuropathy are color blindness (dyschromatopsia) and peripheral field deficits; however, by the time most patients present to the ophthalmologist, decreased visual acuity is usually present. An afferent pupillary defect and pallor of the optic disk on funduscopic examination are found in more advanced cases. Proptosis of the affected eye may also be present, particularly in patients whose disease involves the orbital apex.
INDICATIONS
Optic neuropathy is generally divided into two broad categories—traumatic and nontraumatic. The role of optic nerve decompression for traumatic optic neuropathy has been recently questioned. Current evidence suggests that patients with visual loss from trauma to the optic nerve should be treated with high-dose systemic steroids rather than surgical decompression.
For patients with nontraumatic optic neuropathy, however, optic nerve decompression may prevent further deterioration of the optic nerve or even reverse the visual loss that has already occurred. The most common indications for decompression of the nerve include the following:
Fibro-osseous lesions (e.g., fibrous dysplasia involving the optic canal)
Neoplasms (e.g., meningioma of the optic nerve)
Nonneoplastic masses (e.g., lymphangioma along the lateral sphenoid sinus)
Inflammatory conditions (e.g., Graves’ disease or orbital pseudotumor)
For most patients with optic neuropathy from Graves’ disease, decompression of the orbital apex without formal optic canal decompression is sufficient to alleviate the problem. Some ophthalmologists, however, feel that patients with severe optic neuropathy from Graves’ disease unresponsive to high-dose steroids should undergo optic nerve decompression at the time of orbital decompression.
CONTRAINDICATIONS
Traumatic optic neuropathy (see above)
Acute sphenoid sinusitis (needs antibiotic therapy prior to decompression)
Sphenoid sinus hypopneumatization (may require a neurosurgical approach)
PREOPERATIVE PLANNING
Prior to optic nerve decompression, patients should undergo
CT scan of orbit and sinuses within 1 month prior to surgery
Complete ophthalmologic examination within 1 week prior to surgery
Intravenous steroids (e.g., dexamethasone 12 mg) within 1 hour prior to surgery
SURGICAL TECHNIQUE
The patient is placed in a supine position on the operating table. The eyes are draped into the surgical field and protected with scleral shields. Lidocaine (1%) with epinephrine (1:100,000) is injected along the lateral nasal wall, middle turbinate, and posterior nasal septum.
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