Non-arteritic anterior ischemic optic neuropathy (NAION) refers to loss of blood flow to the optic nerve (which is the cable that connects the eye to the brain). This condition typically causes sudden vision loss in one eye, without any pain. In many cases, the patient notices significant loss of vision in one eye immediately upon waking up in the morning. The visual loss typically remains fairly stable, without getting markedly better or worse once it has occurred.
What causes NAION to occur?
Non-arteritic anterior ischemic optic neuropathy (NAION) is due to impaired circulation of blood to the front of the optic nerve. It is called “non-arteritic” because there is reduced blood flow without true inflammation of the blood vessels (as there is in arteritis). It is called “anterior” because the reduced blood flow and injury to the optic nerve happen at the front-most part of the nerve, where the nerve meets the eye. It is called “ischemic” because that is the word that describes injury due to reduced blood flow. Finally, it is called an “optic neuropathy” because it is an injury to the optic nerve, which disrupts the ability of eye to send information to the brain.
The exact mechanism causing reduced blood flow to the optic nerve in NAION is not proven, but it is known that this condition occurs more often when a patient has conditions such as diabetes, high blood pressure, and sleep apnea. Smoking may also elevate the risk of developing NAION. Most patients with NAION have an anatomical variation of the optic nerve, making its contents very tight and crowded. This anatomy probably contributes to the impaired circulation that causes NAION.
Although it is controversial, some researchers believe that another risk factor for NAION may be the use of blood pressure medications at nighttime, contributing to lower blood pressure during sleep. Another controversy regarding the cause of NAION concerns the use of medications for erectile dysfunction. The link to these medications is not proven, and current studies are trying to carefully address this question.
How will a doctor diagnose NAION?
After taking a thorough history, the doctor will perform a careful examination that includes measuring the visual acuity, color vision, and peripheral visual field. In most cases of ischemic optic neuropathy, the doctor will see swelling of the optic nerve in the back of the eye. Depending on other clinical factors, some blood work may be done to exclude other diseases that affect the optic nerve. For example, it is important to exclude the possibility of Temporal Arteritis, which requires urgent treatment to prevent loss of vision in the other eye. Imaging studies (such as a CT or MRI scan) are not usually needed to diagnose NAION, but might be performed in an atypical case.
How can NAION be treated?
Unfortunately, there are no treatments for NAION that are proven to be effective. There have been many clinical trials studying over a dozen different therapies, but none have convincingly improved the visual outcome in patients with NAION. Some studies have investigated the use of corticosteroids (prednisone) and suggested a mild improvement, but these studies did not use rigorous scientific methods, and it remains unknown if steroids are actually helpful.
Will glasses help correct the loss of vision due to NAION?
Eyeglasses do not correct the vision loss due to NAION. Eyeglasses are used to focus light in front of the eye. With NAION, the problem causing loss of vision is in the back of the eye, where the optic nerve exits to connect to the brain. If the affected eye has a separate problem of near-sightedness or far-sightedness, then glasses can be used for that reason, but they do not help the loss of vision due to an injured optic nerve.
Will NAION affect me again?
Once NAION has occurred in one eye, it is very rare for it to occur again in the same eye. On the other hand, there is approximately a 30% chance that it can occur in the other eye over one’s lifetime.
To try to reduce the risk that NAION occurs in the other eye, the doctor might suggest regular exercise, a healthy diet, and other measures to treat the risk factors of diabetes, high blood pressure, and sleep apnea. For a patient that has had NAION, it is probably reasonable to avoid taking high blood pressure medications before bedtime. It is also often recommended to take daily aspirin, although this treatment is not supported by definite evidence.
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