Non-arteritic anterior ischaemic optic neuropathy (NAION)
Non-arteritic anterior ischaemic 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.
Non-arteritic anterior ischaemic 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 “ischaemic” 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 apnoea. 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 night time, 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.
Unfortunately, there are no treatments for NAION that are proven to be effective.
The role of glasses:
Eyeglasses do not correct the vision loss due to NAION. Eyeglasses are used to focus light in front of the eye such as near-sightedness or far-sightedness. 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.
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 apnoea.
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.