What Is NAION? Causes, Symptoms, and Treatment

NAION is essentially a stroke of the optic nerve, the cable that carries signals from the eye to the brain. Reduced blood flow damages the front of the nerve, and it is the most common sudden optic nerve problem in people over 50.¹ It usually isn’t caused by a blocked artery or a body-wide illness, though a look-alike condition must be ruled out quickly. It comes from an eye built with little room to spare, combined with everyday blood-vessel risks.

What NAION Feels Like When It Happens

Typical NAION is sudden, painless vision loss in one eye, described as blurring or cloudiness.² The loss often affects the lower half of your field of vision, the whole area you can see without moving your eye.³ It may get worse over the following days.⁴ Many people first notice it when they wake up in the morning.⁵

The pattern varies. Some people lose a band of lower vision, others have dimming across the whole field, and others lose the center of vision used for reading.⁶

In daily life, you may only notice it when you cover the good eye, because the other eye fills in the gaps. The lower edge of a page, a step, or a curb may seem missing or smudged. Colors in the affected eye can look washed out. With no redness and no pain, people often wait to see if it clears up, and that is a mistake.

Painless sudden vision loss can also come from a blockage of an artery in the retina or from giant cell arteritis, and only an eye exam can tell these apart. See an eye doctor or go to an emergency department the same day.

At the exam, the doctor will dilate your pupils and look at the back of the eye. A swollen optic nerve at the front, often pale and sometimes pink, is the key sign of NAION. They will swing a light between your eyes to check for a relative pupil defect, which shows the affected nerve isn’t sending signals as well as the other one. Expect a visual field test, where you press a button whenever you see small lights; it maps exactly which parts of your vision are missing. Imaging or blood tests may be ordered at the same visit, mainly to rule out look-alike conditions rather than to confirm NAION itself.

Why NAION Happens

The main risk factor is a small, crowded optic disc, the spot where the nerve leaves the back of the eye.⁷ A crowded disc has little or no central dip, or cup, so the nerve fibers are packed tightly.⁸ The size of the cup is the feature most clearly linked to NAION.⁹

When blood flow dips, the fibers swell, and in a crowded disc that swelling squeezes the small vessels feeding the nerve, which can cut flow further. Normally the nerve keeps its blood flow steady even as blood pressure changes, but some diseases weaken that ability.¹⁰

A crowded disc alone is common, and most people who have one never get NAION. The risk adds up with blood pressure, diabetes, sleep apnea and age. Nothing you did on the day typically caused it. You are born with this disc shape, so the practical focus is on the risks you can influence.

High blood pressure and diabetes play a significant role.¹¹ In one group of NAION patients, 69% had high blood pressure.¹² Among those who thought their pressure was normal, 39% were found to have high blood pressure on 24-hour monitoring.¹³ A new NAION diagnosis is a good reason to have your blood pressure checked properly.

Because vision loss is often noticed on waking, doctors have suspected that blood pressure falling too low during sleep is a final trigger.¹⁴ Some NAION patients show unusually deep drops in blood pressure overnight.¹⁵ Not every study finds this deep-dip pattern linked to other NAION risks, though.¹⁶ Ask your doctor before moving blood pressure pills to bedtime, since that can deepen night dips.¹⁷

Obstructive sleep apnea, where breathing repeatedly stops during sleep, is linked to roughly 3 to 4 times the odds of NAION.¹⁸ In another analysis, untreated apnea without a CPAP machine carried a 16% higher risk.¹⁹ Whether treating sleep apnea protects the eye isn’t yet known.²⁰ If you snore heavily or wake unrefreshed, ask about a sleep test.

Blood clotting plays a part too. People with one copy of the inherited clotting trait factor V Leiden were about twice as likely to have NAION.²¹ High fibrinogen, high triglycerides and low HDL cholesterol have also been linked to it.²²

Can Viagra or Other Medicines Cause NAION

Among men taking sildenafil, about 2.8 cases per 100,000 per year occurred, similar to the general rate in people over 50.²³ Erectile dysfunction and NAION share risks such as diabetes and high blood pressure, so a link is hard to untangle.²⁴ No strong proof shows these pills cause NAION.²⁵ Still, they have been proposed as possible risk factors in related optic nerve damage.²⁶ The heart rhythm drug amiodarone is also listed as a possible risk factor.²⁷

Never stop a heart drug like amiodarone without your doctor. After NAION in one eye, many doctors advise avoiding ED pills to be safe. Bring a full medicine list to your eye appointment.

Will Your Vision Come Back

Vision often worsens over about 2 weeks and then stays stable.²⁸ After that, any improvement or worsening mostly happens within 6 months, with little change after.²⁹ Once the nerve swelling clears, sharpness of vision does not seem to worsen.³⁰

Among people seen within 2 weeks with vision of 20/70 or worse, about 41% improved by 6 months without treatment.³¹ Field of vision improved in about 26%.³² But within 2 years, 18% of those starting with poor vision got worse.³³ In one large trial, at 6 months 35% of eyes saw better than 20/64 while 36% were worse than 20/200.³⁴

The worsening early on is part of the usual course: in the first days to weeks the swollen nerve can keep losing function, and it doesn’t by itself mean something new is going wrong. After about two weeks, change usually slows. A sudden new drop long after the first attack deserves a prompt call, as it could be a different problem.

Improvement is often partial, such as a blurry area getting smaller or letters becoming a little clearer, rather than a return to the vision you had before. Some people regain better reading ability while the field defect stays, and others see the opposite, so sharpness and field of vision can change independently. The percentages describe groups and can’t tell you which group you will fall into, so doctors usually speak in ranges.

Follow-up visits repeat the vision and visual field tests, and scans measure nerve fiber thinning over months. A pale nerve later on is expected scarring, not a new attack.

Ruling Out Giant Cell Arteritis

A similar optic nerve stroke can be caused by giant cell arteritis (GCA), an inflammation of medium and large arteries. When it affects the artery feeding the optic nerve it can cause vision loss that looks much like NAION. Without high-dose steroids it can blind the second eye within days to weeks, which is why doctors check for it before assuming NAION. When suspicion is strong, they often start high-dose steroids right away without waiting for every test, because delay can cost sight.

Tests help separate the two. In GCA, blood markers of inflammation (ESR and CRP) and platelet counts are much higher than in NAION.³⁵ An MRI of the eye socket often shows inflammation around the nerve in GCA but rarely in NAION.³⁶ Months later, the nerve’s central cup often enlarges after GCA but usually not after NAION.³⁷

Tell your doctor right away about any signs that can point to GCA: new headache or scalp tenderness, jaw pain when chewing, fever, weight loss, aching shoulders, or brief vision blackouts before the loss.

Treatment Options and What the Evidence Shows

In one large clinic series, 70% of eyes treated early with steroid pills improved, versus 41% untreated.³⁸ But a pooled analysis of 720 eyes found steroids did not improve sharpness of vision.³⁹ So some doctors offer steroids and others don’t.

The 70% result came from a clinic series where patients chose treatment, not from a trial that randomly assigned people, so differences between groups may explain part of it. Steroids seem to help swelling resolve sooner, but resolving swelling is not the same as restoring vision. And because NAION improves on its own in many people, a treatment can look good simply because some would have improved anyway.

Treatment is usually a course of oral steroids started early, within the first couple of weeks, and then tapered. Steroids raise blood sugar and blood pressure, and can cause trouble sleeping and mood changes, which matter for people already managing diabetes or hypertension. Doctors weigh these against the uncertain benefit, so the choice should follow a discussion of your own health conditions.

Surgery to relieve pressure on the nerve was tested in a major trial.⁴⁰ But 33% of surgery patients improved versus 43% with careful follow-up, and 24% worsened versus 12%.⁴¹ The surgery is no longer recommended.⁴²

Other treatments are under study. An experimental eye injection did not meet its main goal in a trial.⁴³ It did help preserve vision in people starting at 20/63 or worse, and was well tolerated.⁴⁴ In early human studies, erythropoietin and citicoline showed some nerve-protecting effect.⁴⁵

Useful questions for your doctor: whether steroids are worth it in your case and what their risks are, and whether a clinical trial is open to you if you’re seen early. Be wary of clinics selling unproven cures.

Protecting Your Other Eye

In a large trial, about 1 in 6 to 1 in 10 people had NAION in the other eye over follow-up.⁴⁶ The other eye usually shares the same crowded disc.

Aspirin may help. In one study, second-eye NAION occurred in 18% of people taking aspirin 325 mg daily versus 50% of those without.⁴⁷ Another study found fewer second-eye cases with regular aspirin.⁴⁸ These were small or look-back studies, not trials. Ask your doctor before starting aspirin, which can cause bleeding.

Everyday steps matter more than any single pill. Get your blood pressure checked, including overnight if advised. Control diabetes and cholesterol. Get tested for sleep apnea and use CPAP if it’s prescribed. And report any new blurring in the good eye the same day.

Living With Vision Loss From NAION

People with NAION report the biggest problems with driving, everyday roles and social life.⁴⁹ Mental health and independence are moderately affected.⁵⁰ Vision training targeting remaining sight improved reading speed in a small study.⁵¹

Driving and work are hardest because losing vision in one eye reduces depth perception and the side field of vision on the affected side, which makes judging distance and spotting cars harder. Jobs that need fine detail, reading, or judging distance may need changes, such as better lighting or larger screens. Many people regain confidence as the brain adapts over months, though some activities remain harder.

Check local rules on driving with one-eye vision loss. Turn your head to scan the missing area. Use brighter lighting and high-contrast markings on steps, and ask about low-vision services.