What is anterior ischemic optic neuropathy?

Anterior ischemic optic neuropathy (AION) is a sudden loss of vision due to an interruption of blood flow to the front (anterior) of the optic nerve, also known as the optic nerve head.

The optic nerve’s job is to carry visual information from the eye to the brain, which assembles this information into images. About 1.2 million tiny fibers in the optic nerve rely on oxygen and nutrients supplied by surrounding blood vessels. Any interruption in blood supply can damage vision. The more the optic nerve is damaged, the greater the vision loss.

What are the symptoms of anterior ischemic optic neuropathy?

There are 2 forms of AION, each with their own particular set of symptoms.

Arteritic AION (A-AION) is a dangerous condition caused by inflammation of arteries supplying blood to the optic nerve. The inflammation is due to a condition known as giant cell arteritis (GCA) or temporal arteritis, which causes inflammation of medium- and large-sized arteries. GCA is potentially fatal and can damage the entire optic nerve head leading to permanent, massive vision loss if not diagnosed and treated quickly. A-AION is found 3 times more often in women than men, and most often affects those over the age of 55.

GCA usually presents a number of symptoms before any loss of vision occurs. About 80% of those affected will feel unwell for some time with any of the following:

  • Pain in the temples
  • Pain when chewing
  • Scalp pain or tingling
  • Neck pain
  • Muscle aches and pains, particularly in the upper legs or arms
  • General fatigue
  • Loss of appetite
  • Unexplained loss of weight
  • Fever

In a less common form of GCA known as occult giant cell arteritis, no symptoms are present.

The key vision-related symptom of A-AION is painless, temporary blurriness or loss of vision lasting several minutes or hours before vision loss becomes permanent. This temporary vision loss should be taken as a warning signal. Whether 1 or both eyes are permanently affected depends on how soon the patient is seen by an eye doctor, how soon a diagnosis is made, and how quickly treatment begins.

Nonarteritic AION (NA-AION) is the most common form of AION. The majority of those affected are over the age of 50; 10% of cases are in people over age 45. However, the condition can appear at any age. Both men and women have the same rates of occurrence. NA-AION is caused not by inflammation of the arteries but by one of the following: (1) a drop in blood pressure to such a degree that blood supply to the optic nerve is decreased; (2) increased pressure inside the eyeball; (3) narrowed arteries; (4) increased blood viscosity (thickness); or (5) decreased blood flow to the optic nerve where it leaves the back of the eye. A number of diseases or conditions can cause these risk factors, putting a person at greater risk of developing NA-AION.

Risk factors include:

  • High blood pressure
  • Diabetes mellitus
  • High cholesterol
  • Smoking
  • Sleep apnea
  • Heart disease
  • Blocked arteries
  • Anemia or sudden blood loss
  • A sudden drop in blood pressure
  • Sickle cell trait
  • Vasculitis (inflammation of a blood vessels)

The main symptom of NA-AION is a sudden, painless loss or blurring of vision in one eye, usually noticed upon waking from a night’s sleep or even a nap. It is believed that the body’s normal drop in blood pressure during sleep ― along with one or more underlying risk factors ― triggers an interruption of blood flow to the optic nerve.

Note that there is no correlation between a person having poor eyesight (being nearsighted or farsighted) and the development of NA-AION.

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