Patient Selection and Indications

Optic neuropathy is generally divided into two broad categories: traumatic and nontraumatic. The most common indication for optic nerve decompression historically has been traumatic optic neuropathy.

The role of optic nerve decompression for traumatic optic neuropathy is controversial and early studies suggest that neither corticosteroids nor surgical optic nerve decompression offers benefit over observation. ⁴ In order to answer this question, a randomized controlled trial named the International Optic Nerve Trauma Study (IONTS) was created but struggled with patient recruitment. The protocol was changed to a nonrandomized study of 127 patients and found no benefit of corticosteroids or surgical decompression. The final study recommendations were that patients with visual loss from trauma to the optic nerve should be first treated with high-dose systemic steroids rather than surgical decompression but that treatment should be individualized for each patient. ⁵ Multiple retrospective studies subsequent to the IONTS have suggested improvement in visual acuity with optic nerve decompression following failure of visual improvement with steroids. ^{6,​ 7,​ 8}

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. Neuropathy with vision loss is most likely due to direct neuronal compression leading to a conduction block and resultant demyelination. Therefore, many patients experience rapid recovery following pressure release and continued recovery as the nerve continues to remyelinate. ⁹ The most common indications for such decompression are the following:

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  Fibro-osseous lesions (e.g., fibrous dysplasia involving the optic canal).

  
  
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  Neoplasms (e.g., meningioma of the skull base).

  
  
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  Non-neoplastic masses (e.g., lymphangioma along the lateral sphenoid sinus).

  
  
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  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 address the pathology. 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.

11.3 Diagnostic Workup

In traumatic optic neuropathy, patients are often involved in high-speed or multisystem trauma and should first be evaluated by a trauma team. A computed tomography (CT) scan should be performed to evaluate for orbital, orbital apex, or skull base injuries. In nontraumatic optic neuropathy, most patients initially present with complaints of blurred or hazy vision with a normal funduscopic exam. Prior to optic nerve decompression, a complete ophthalmologic examination should be performed within 1 week prior to surgery. Often this examination may reveal visual field defects, change in color vision (dyschromatopsia), afferent pupillary defect, or even optic disc pallor in advanced disease. A magnetic resonance imaging (MRI) with and without contrast may be obtained to radiographically evaluate the optic nerve. Once optic nerve compression has been diagnosed, systemic corticosteroids may provide some relief while awaiting surgical intervention.

11.4 Surgical Anatomy

The optic nerve may be divided into three segments: intraorbital, intracanalicular, and intracranial. Optic nerve decompression aims to relieve compressive forces within the intracanalicular portion of the nerve. The canal of the optic nerve is formed by the two struts of the lesser wing of the sphenoid and carries both the optic nerve and the ophthalmic artery.

11.5 Surgical Technique

The patient is placed in a supine position on the operating table. The eyes are draped in 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.

If necessary for adequate surgical exposure, the surgeon should perform a septoplasty or resect the middle turbinate at the beginning of the procedure. A sphenoethmoidectomy is then performed in the standard fashion. The sphenoid face is opened widely, and the prominence of the bony optic nerve canal is identified as it courses along the lateral wall of the sphenoid sinus, just superior to the opticocarotid recess ( ▶ Fig. 11.1). The astute surgeon should be aware that the optic canal can be located within a posterior ethmoid or Onodi cell, which can be identified on preoperative CT scan. In such cases, widely opening the Onodi cell is an important step to provide adequate surgical exposure. An image-guidance system may be used at the surgeon’s discretion to assist with the identification and verification of the location the optic canal.

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