Non-arteritic anterior ischemic optic neuropathy (NAION) is the most common cause of optic nerve swelling and optic neuropathy in adults over 50 years of age.
Risk factors that have been strongly associated with NAION include hypertension, hypercholesterolemia, diabetes mellitus, cardio- and cerebrovascular disease, and obstructive sleep apnea.
While the exact pathogenesis of a NAION has not been elucidated, the prevailing theory is that it is caused by hypoperfusion of the short posterior ciliary arteries supplying the optic nerve, which then causes ischemia which induces swelling of the portion of the optic nerve traveling through the small opening in a scleral canal. This, in turn, leads to the compartment syndrome involving neighboring axons that are now compressed in a space limited by the small opening in the scleral canal, leading to apoptosis and death of the ganglion cells whose axons comprise the optic nerve.
The natural history of NAION has been elucidated in Ischemic Optic Neuropathy Decompression Trial which demonstrated that about 30% of patients would regain 3 or more lines of vision at 2 years follow up, 20% will lose 3 or more lines of vision and in the majority of patients, the vision will remain unchanged after the onset. In reality, visual acuity will not change in the vast majority of patients after the acute event has resolved, and the ones who are able to see a few lines better likely learned to improve their fixation.
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