Anterior Ischemic Optic Neuropathy

What is Anterior Ischemic Optic Neuropathy?

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

The optic nerve carries visual information from the eye to the brain, which assembles that information into the images we see. The nerve’s roughly 1.2 million tiny fibres depend on the oxygen and nutrients supplied by the surrounding blood vessels, so any interruption in this blood supply can harm vision. The more extensive the damage to the optic nerve, the greater the loss of vision.

There are two types of AION. Arteritic AION (A-AION) is caused by inflammation of the arteries that supply blood to the optic nerve. Non-arteritic AION (NA-AION) is caused by factors other than arterial inflammation. Treatment differs depending on whether or not the nerve itself has been damaged.

What are the symptoms of Anterior Ischemic Optic Neuropathy?

There are two forms of AION, each with its own particular set of symptoms:

Arteritic AION (A-AION)

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

GCA usually causes a number of symptoms before any vision is lost. Around 80% of those affected will feel unwell for some time, with any of the following:

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

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

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

Non-arteritic AION (NA-AION)

Non-arteritic AION (NA-AION) is the most common form of AION. The majority of those affected are over the age of 50, and 10% of cases occur in people under the age of 45; however, the condition can appear at any age. Men and women are affected in equal numbers.

NA-AION is caused not by inflammation of the arteries but by one of the following:

(1) a drop in blood pressure severe enough to reduce the blood supply to the optic nerve

(2) raised intraocular pressure

(3) narrowed arteries

(4) increased blood viscosity (thickness)

(5) reduced blood flow to the optic nerve where it leaves the back of the eye.

A number of diseases and conditions can produce 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 apnoea
• Heart disease
• Blocked arteries
• Anaemia or sudden blood loss
• A sudden drop in blood pressure
• Sickle cell trait
• Vasculitis (inflammation of the blood vessels)

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

Note that there is no link between poor eyesight (being short-sighted or long-sighted) and the development of NA-AION.

How is Anterior Ischemic Optic Neuropathy diagnosed?

• Tests of visual acuity (sharpness of vision) and the visual field (to gauge any loss of central or peripheral vision).
• Measurement of intraocular pressure.
• A dilated eye examination to detect any damage to the optic nerve.
• Measurement of overall blood pressure.
• Blood tests for the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), together with a platelet count (CBC).
• Further blood tests to detect conditions such as diabetes, vascular disease, anaemia or high cholesterol.
• A biopsy of the arteries at the temple to determine whether arterial inflammation is present.
• Injection of dye into the arteries of the head for fluorescein angiography, in which photographs of the blood vessels are taken to show where blood flow may be interrupted.

How is Anterior Ischemic Optic Neuropathy treated?

• Treatment of NA-AION

Treatment focuses on the underlying cardiovascular disease or other risk factors that help trigger and aggravate NA-AION. Controlling these can help manage the condition and prevent further loss of vision.

Studies of several surgical and medical therapies have shown no improvement in outcome for NA-AION compared with observation alone.

• Treatment of A-AION

Managing A-AION is, in effect, the same as managing giant cell arteritis: prompt, accurate diagnosis followed by immediate, emergency-level corticosteroid treatment. High doses of steroids are given for two to three weeks and then tapered over time, but a lifelong low-dose regimen is usually needed to prevent blindness. In every case, the results of ESR and CRP tests — together with the patient’s symptoms — should guide the steroid dose.

How can Anterior Ischemic Optic Neuropathy be prevented?

Controlling the risk factors associated with NA-AION is an important preventive measure.

In addition, people with risk factors should avoid taking blood pressure-lowering medications or erectile dysfunction drugs before bedtime. Combined with the normal fall in blood pressure during sleep, these drugs could be enough to interrupt the blood supply to the optic nerve.

For A-AION, continued use of corticosteroids is recommended to prevent further loss of vision, and close follow-up with a rheumatologist is needed.

What is the outlook for someone with Anterior Ischemic Optic Neuropathy?

A-AION usually causes a greater degree of vision loss than NA-AION. The extent of the loss depends on the location and amount of optic nerve damage. Some patients suffer severe loss of vision in one eye only and retain the use of the other eye, although there may be some loss of peripheral (side) vision. There may also be difficulty detecting contrast between light and shade, as well as reduced colour vision. A-AION often shows minimal or no improvement.

In NA-AION, about 40% of patients show some improvement in central vision in the months following the loss of vision or visual field, although 20-25% of patients with AION in one eye will develop AION in the other eye within three years. Only about 5% of patients have repeated episodes of AION in the same eye, and a small number may find their vision worsening over time. This usually occurs after the first two to three weeks.