Optic Nerve Decompression for Traumatic Optic Neuropathy Workup

Updated: Nov 05, 2018
  • Author: Christie Anne Barnes, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Laboratory Studies

Hemostasis is essential during optic canal decompression. Obtain the following tests as suggested by the patient's medical history:

  • Hemoglobin/hematocrit

  • Platelet count

  • Prothrombin time (PT)/activated partial thromboplastin time (aPTT)

  • Bleeding time

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Imaging Studies

Perform thin-slice CT scanning of the nose, sinuses, and orbits. CT scanning provides adequate imaging of orbital soft tissue and is better than MRI at delineating bony defects. A thin-section CT scan also provides an intraoperative road map for the surgeon in patients who require surgical decompression.

The decision for surgical decompression should still be based primarily on the clinical examination findings and not the CT scan findings. Small-review series have concluded that the extent of bony canal injury documented at surgery was underestimated by CT scan findings.

In polytraumatized patients with poor awareness, CT scan with clinical exploration is the most important method for the assessment of traumatic optic neuropathy in the acute emergency setting. Fractures through the optic canal can be best depicted with thin-section CT scanning (eg, 1.5-mm cuts with 1-mm intervals).

Surgeons who wish to perform image-guided optic canal decompression need to obtain a special-order CT scan that is formatted to their computerized stereotactic localizing system.

Diffusion tensor magnetic resonance imaging (DT-MRI) may provide valuable information for evaluating the fibers of the optic nerve in traumatic optic neuropathy. [14, 15]

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Other Tests

Patients suspected of sustaining traumatic optic neuropathy should undergo visual field testing. Although no visual field defects are pathognomonic of traumatic optic neuropathy, quantification of visual field defects is useful to assess convalescent visual improvements. Simple visual field screening can be accomplished at the bedside for unstable patients, but formally assess patients who can be evaluated in the clinic setting.

Multifocal visual-evoked potential (VEP), multifocal electroretinography (mfERG), and optical coherence tomography are 3 promising techniques in the future diagnoses of subclinical vision loss. Some of these tests are already used in neuro-ophthalmology for the studies of the retina and glaucoma. Although none of these techniques should replace a careful history and clinical examination, these techniques might be important as adjunct procedures in the evaluation of the unconscious patient or patients with bilateral optic neuropathy. Flash visual-evoked potential (FVEP) was studied in patients with traumatic optic neuropathy with calculation of a ratio of the amplitude of the injured to the uninjured eye. A ratio of greater than 50% was associated with favorable visual outcome. [16]

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Histologic Findings

Histopathology is not integral to the clinical management of traumatic optic neuropathy. Clinicopathologic studies, however, have anecdotally demonstrated several features of traumatic optic neuropathy, as follows:

  • Blood within the optic nerve sheath

  • Interstitial optic nerve hemorrhage

  • Fibrosis of the pial septa

  • Lymphoplasmacytic infiltration

  • Iron-laden macrophages

  • Triangular-shaped axonal degeneration with loss of myelin

  • Ischemic necrosis

The time-dependent histopathologic changes of the optic nerve following indirect trauma have not been adequately described.

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