A traumatic optic neuropathy is one caused by trauma to the optic nerve, most frequently in the setting of a traffic accident with cranial and/or midface fractures.
Traumatic optic neuropathy results primarily from indirect injury, rather than by direct crushing or tearing mechanisms. A direct blow to the eye can cause an avulsion of the optic nerve (more properly called an expulsion). The mechanism appears to be one of a sudden, explosive increase in intraocular pressure with rupture of the scleral coat in a circumpapillary ring where the sclera is very thin. Most often, this occurs in patients that have moderate to high degrees of axial myopia and/or a posterior staphyloma. The eye has no light perception, the pupil is fixed in mid-dilation, and ophthalmoscopy reveals disappearance of the optic disc, with folds of retina that have been dragged through the posterior rupture. Another mechanism appears to be a small-vessel infarction of the intracanalicular portion of the nerve, presumably caused by shearing of the perineural blood vessels. This commonly happens without a fracture, and there is initially no ophthalmoscopic abnormality. The eye has no light perception, there is a normal disc appearance, and there is a profound RAPD. When seeing acutely injured patients, as in an emergency room setting, the single most important bit of objective data is the presence or absence of an RAPD. The disc will often be normal in appearance, only to develop manifest atrophy over the ensuing 6 weeks. Penetrating orbital injury with direct damage to the optic nerve is much less common. Treatment in this setting is controversial. Despite many attempts to study this problem, it is not known whether (1) surgical decompression of the orbit and/or optic canal, (2) removal of orbital bone fragments in contact with the nerve, or (3) conservative management with high doses of intravenously administered corticosteroids is the better method. Megadose cor-ticosteroids are most commonly used, since the surgical approaches carry the additional risk of high morbidity with uncertain benefit.
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