Sudden, Painless Vision Loss: What You Need to Know About Ischemic Optic Neuropathy

Imagine waking up one morning and noticing a sudden change in your vision—perhaps a dark shadow in your field of view or significant blurriness. If this vision loss occurs without pain, it could be a sign of ischemic optic neuropathy (ION)—a rare but serious eye disease caused by poor blood flow to the optic nerve.

What is Ischemic Optic Neuropathy?

The optic nerve is responsible for transmitting visual signals from the eyes to the brain. If it does not receive enough oxygen due to a disruption in blood flow, it can lead to irreversible vision loss. This is called an ischemic event, similar to what occurs in a stroke but affecting the optic nerve instead of the brain.

There are two types of ischemic optic neuropathy, each with different causes, risk factors, and symptoms.

Non-Arteritic Ischemic Optic Neuropathy (NAION)

NAION is the most common form of ischemic optic neuropathy. It typically affects adults between 40 and 60 years old and usually impacts only one eye.

Causes of NAION

The exact cause of NAION is not always clear, but it has been linked to several underlying conditions, including:

• Diabetes
• High blood pressure (hypertension)
• High cholesterol
• Anemia
• Sleep apnea

Additionally, individuals with a “disc at risk”—a small, crowded optic nerve structure—are more vulnerable. In these cases, the blood vessels supplying the nerve are more easily compressed, reducing blood flow.

Symptoms of NAION

• Sudden vision loss in one eye
• Loss of peripheral (side) vision, often in the upper or lower half
• Blurry or dim central vision

Unlike other eye diseases, NAION does not cause pain. Once vision loss occurs, the condition usually stabilizes, but in about 35 percent of cases, it progressively worsens. Some patients, however, experience slight vision improvement over several months.

Treatment for NAION

There is no cure for vision loss caused by NAION. However, managing underlying conditions like high blood pressure and sleep apnea may reduce the risk of further vision loss. A comprehensive medical evaluation, including blood work and sleep studies, is essential for identifying potential causes.

Arteritic Ischemic Optic Neuropathy (AION)

AION is a more severe and urgent form of ischemic optic neuropathy. It is linked to Giant Cell Arteritis (GCA)—a systemic inflammatory disease that causes swelling in the arteries and severely restricts blood flow.

Who is at Risk for AION?

AION primarily affects adults over 55 years old and typically starts in one eye. If untreated, it can affect both eyes within a few days to a week.

Symptoms of AION and Giant Cell Arteritis

• Severe vision loss, often worse than in NAION
• Headache
• Pain while chewing
• Scalp tenderness, especially near the temples
• Unexplained weight loss, muscle or joint pain, or fever



Since AION is caused by inflammation, immediate medical intervention is critical.

Diagnosis and Treatment of AION

If AION is suspected, blood tests—including ESR (erythrocyte sedimentation rate), CRP (C-reactive protein), and platelet count—are ordered. A temporal artery biopsy may also be necessary to confirm Giant Cell Arteritis.

Unlike NAION, AION can be prevented from progressing. If GCA is diagnosed, high-dose steroids must be started immediately to reduce inflammation and prevent blindness in the other eye.