Laboratory Studies
Hemostasis is essential during optic canal decompression. Obtain the following tests as suggested by the patient's medical history:
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Hemoglobin/hematocrit
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Platelet count
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Prothrombin time (PT)/activated partial thromboplastin time (aPTT)
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Bleeding time
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 scanning 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. [2, 3]
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. [20]
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:
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Blood within the optic nerve sheath
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Interstitial optic nerve hemorrhage
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Fibrosis of the pial septa
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Lymphoplasmacytic infiltration
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Iron-laden macrophages
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Triangular-shaped axonal degeneration with loss of myelin
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Ischemic necrosis
The time-dependent histopathologic changes of the optic nerve following indirect trauma have not been adequately described.
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Endoscopic view of the intranasal anatomy: (1) lateral nasal wall, (2) middle turbinate, and (3) nasal septum.
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Endoscopic view after intranasal ethmoidectomy. The ethmoid air cells have been removed, exposing the orbit. The black line delineates an intact orbit prior to decompression.
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The first step in orbital decompression is depicted in this endoscopic view of the right eye. A curette can be observed. The surgeon is removing the thin bone covering the orbit (the lamina papyracea of the right orbit).
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This image depicts exposure of the orbital contents as the lamina papyracea is removed. The arrow points to the orbit without its bony coverage.
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The next step in orbital decompression is depicted. After the lamina papyracea is removed, a sickle knife is used to incise the orbital periosteum to allow the orbit to herniate into the sinuses, thus reducing orbital pressure. The black line highlights the limits of the orbit.
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empty para to satisfy content model
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This image represents the successful decompression of the orbit. The periorbital fat that encases the orbit can be seen herniating into the intranasal cavity (1). This procedure reduces the intraorbital pressure.
