Non-arteritic ischemic optic neuropathy (NAION) is an eye condition that may restrict blood flow to the optic nerve. This results in painless, sudden-onset vision loss in one eye.

Doctors do not know what causes NAION, but they think it could be related to sleep apnea and certain medications, such as sildenafil (Viagra). However, other health conditions, such as diabetes and hypertension, can increase a person’s likelihood of developing NAION.

NAION is the most common cause of sudden-onset optic nerve damage in people over 50.

Read on to learn more about NAION, including what causes it and how doctors diagnose and treat it. This article also provides answers to some frequently asked questions about NAION.

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“Ischemia” is the term doctors use when a part of the body stops getting enough oxygen as a result of restricted blood flow. This is because blood carries oxygen in the body. In the case of NAION, this lack of oxygen affects the optic nerve.

NAION is one of two types of anterior ischemic optic neuropathy (AION). Both types of AION affect the optic disc, a 1-millimeter segment of the head of the optic nerve, causing visible swelling of the disc.

Arteritic anterior ischemic optic neuropathy (AAION) presents with inflammation of the arteries that supply the optic nerve. However, NAION — the non-arteritic type — does not affect the optic nerve arteries in this way.

Symptoms of NAION include:

  • sudden, painless loss of vision in one eye
  • blurring or cloudiness, often when gazing downward
  • headache or pain around the eye, in rare cases

Additionally, clinical signs may include:

  • acute swelling of the optic disc
  • optic disc hemorrhage
  • altitudinal field loss (loss of vision in the horizontal half of the field of vision)
  • chronic deterioration of the optic nerve

Learn more about ischemic optic neuropathy.

Researchers have not found the definitive cause of NAION but have suggested some possible reasons people may develop it, including certain conditions and medications.


Studies suggest that people with sleep apnea are at a significantly higher risk of developing NAION, even when researchers control for confounding factors.

Researchers have not found the underlying mechanism for this, but it might be related to spells of apnea (when a person stops breathing temporarily). The apnea could cause sharp increases in blood pressure and intracranial pressure (pressure inside the skull) or low blood oxygen levels at night. This could lead to fluid buildup and a lack of oxygen in the optic nerve.

Some conditions cause changes in the blood vessels. Doctors call these vasculopathic conditions. Vasculopathic risk factors that can lead to NAION include:

  • diabetes mellitus
  • high blood pressure
  • tobacco use


Additionally, certain medications could potentially cause NAION. The authors of a 2016 review suggest that when a doctor diagnoses NAION, they should check whether the person took any PDE-5 inhibitors, such as sildenafil, before they lost their vision.

If a person has NAION in one eye and is taking this medication, their doctor should warn them that continued use may increase their risk of developing NAION in the other eye.

If a person has a history of NAION, doctors should use caution in prescribing sildenafil for pulmonary hypertension or erectile dysfunction because of the risks to the eyes.

People with the following conditions are at higher risk of developing vasculopathy:

  • diabetes
  • hypertension
  • atherosclerosis
  • endothelial dysfunction, a condition affecting the lining of the blood vessels

A 2021 review added hyperlipidemia and small cup-to-disc ratio (the ratio of the diameter of the optic disc cup to the total diameter of the optic disc) to the list of potential risk factors for NAION.

A study published in the British Medical Journal supports these findings, noting that people with metabolic syndrome are more likely to experience NAION.

To determine whether a person has NAION, a doctor will take their medical history and examine the eye. This involves measuring the following aspects of a person’s eye:

  • Visual acuity: This is the eye’s ability to distinguish shapes and details of objects at a certain distance.
  • Color vision: This is the eye’s ability to identify differences between light formed of different frequencies regardless of the intensity of the light.
  • Pupils: A relative afferent pupillary defect causes the pupils to respond differently to light shone in one eye at a time.
  • Peripheral visual field: This is the entire area the eye can see.

A doctor will also check the appearance of the retina and optic disc for signs such as swelling and splinter hemorrhages. In some people, the eye may also leak pus.

The authors of a 2022 article in Frontiers in Ophthalmology suggest that treating NAION effectively may require a combination of therapies to tackle different inflammatory mediators at different points in the disease timeline. This is because people with NAION tend to visit their eye doctor days to weeks after the initial loss of vision, rather than within hours.

Researchers continue to explore neuroprotective treatments that protect the nerve cells by suppressing the inflammatory response after the initial eye injury.

They are also looking into treatments that could regenerate the damaged nerve, such as through transplantation of retinal ganglion cells — neurons that connect the eye input to the visual processing centers of the central nervous system.

Steroid treatment

Research suggests some controversy surrounding steroid treatment for NAION. For instance, the authors of a 2019 analysis reported that neurologists often prescribe steroids for NAION. However, the analysis found that steroids do not significantly improve visual acuity. These medications also come with a long list of side effects.

Reducing complications

To reduce NAION risk factors that have an association with blood vessel health, a person may benefit from:

  • stopping smoking, if applicable
  • losing excess weight, if applicable
  • exercising

Below are some frequently asked questions about NAION.

Can it come back after being treated?

Yes, NAION can come back after treatment.

One review and meta-analysis published in BMC Ophthalmology found that using preventive therapies after the initial event does not prevent NAION from developing in the other eye.

However, if NAION gets worse or comes back more than 2 months after it first developed, the diagnosis of NAION may not be correct and a person should go back and discuss their symptoms with their doctor.

What is the outlook for the condition?

A person’s vision can worsen in the 2 weeks after the initial event but typically stabilizes within 2 months. Generally, younger people have a better chance of regaining their vision.

Can glasses help correct some vision loss due to NAION?

NAION is a problem relating to the connection between the optic nerve and the brain.

Eyeglasses help focus light correctly onto the retina, so they cannot improve NAION symptoms. However, they may help if a person also has another eye problem, such as nearsightedness or farsightedness.

NAION is an eye condition that causes sudden, painless vision loss in one eye.

Doctors do not know exactly what causes the condition, but sleep apnea and certain medications, such as sildenafil (Viagra) and the cancer medication interferon alpha, may contribute.

Additionally, people with diabetes, hypertension, and a small cup-to-disc ratio of the eye have a higher risk of developing NAION.

No definitive treatment for NAION exists, but stopping smoking, losing weight, and exercising may help some people manage the condition.