An “eye stroke” is a term used to describe several different conditions that lead to vision loss because of poor blood flow to the eye. Only some of these conditions occur by similar mechanisms as brain strokes. The most common of these conditions include:
• Ischemic optic neuropathy from giant cell arteritis (also known as temporal arteritis)
• Non-arteritic anterior ischemic optic neuropathy (NAION)
• Retinal vein occlusion
• Retinal artery occlusion
Non-arteritic anterior ischemic optic neuropathy
Non-arteritic anterior ischemic optic neuropathy (NAION) is a potentially debilitating condition that occurs from a lack of sufficient blood flow to the optic nerve. If you have sudden vision loss, contact your doctor immediately.
Causes of NAION
The exact cause of NAION is not fully understood. NAION causes damage to the optic nerve. The optic nerve is the cable that connects the brain to the eye and carries millions of nerve fibers and blood vessels.
Although sometimes there can be total blockage of a blood vessel that feeds the optic nerve, it is believed to be more commonly caused by inadequate flow to one half of the nerve. If the optic nerve's nutrient and oxygen supply is cut off, nerve tissue is damaged, resulting in vision loss.
Symptoms of NAION
People with NAION usually have no warning before vision loss occurs. Most patients notice a loss of vision in one eye upon waking in the morning with no pain. Some people notice a dark area or shadow in their vision that affects the upper or lower half of their visual field. Other symptoms include loss of contrast and light sensitivity.
Diagnosis of NAION
If your doctor suspects that you had NAION, he or she will review your medical history and ask about cardiovascular disease and conditions you may have such as diabetes, hypertension or high cholesterol. You will undergo a complete eye exam including dilatation of your eyes to examine your optic nerve and retina.
Typically in NAION the optic nerve will appear swollen. Your doctor will also carefully assess your symptoms to distinguish NAION from other types of eye stroke. One type, known as giant cell arteritis, carries additional risk of the other eye being affected if left untreated and loss of vision could occur in both eyes. Your doctor will ask you about symptoms of giant cell arteritis such as fever, headache, scalp tenderness, jaw pain, weight loss, loss of appetite and fatigue.
Risk Factors of NAION
NAION is more common in middle-aged people and the elderly. Cardiovascular disease raises your risk for developing the disease. In some patients with cardiovascular disease, it is believed that blood pressure falling while sleeping may lead to poor blood flow to the optic nerve and increase the risk of NAION. High cholesterol, diabetes, obstructive sleep apnea, age, and use of certain medications may also increase your risk.
Every person has a different shape of their optic nerve, and some shapes can raise your risk of eye stroke. If the hole that the nerve fibers travel through is smaller than average, the nerve fibers can become crowded. When they become crowded, the risk of developing NAION increases.
Treatment of NAION
There are no proven medications to treat NAION. The amount of vision loss is usually stable but may worsen over the first couple of weeks. Recommendations include optimizing vascular risk factors. It is important to address your risk factors in order to attempt to prevent NAION from occurring in your other eye. Studies have found that there is an approximately 15 percent chance that it will happen to the other eye within one year. Clinical trials are underway to explore advanced treatments for NAION.