Neuro-Ophthalmology · Patient Series
You wake up and part
of one eye is gone.
The optic nerve had a stroke.
Non-arteritic anterior ischemic optic neuropathy, or NAION, is the most common sudden optic nerve injury after 50. It is painless, it often shows up first thing in the morning, and it now has a new name attached to it in the news: semaglutide. Here is what happens inside the nerve, who is at risk, and what the evidence says about getting vision back.
at onset
within 5 years
(EMA estimate)
Section 01 — What Actually Happens
A traffic jam
at the back of the eye.
About 1.2 million nerve fibres leave the retina through a single opening at the back of the eye, the optic disc, which is roughly 1.5 to 2 mm across. They squeeze through a sieve of connective tissue and head for the brain. The blood that keeps them alive arrives through small branches of the short posterior ciliary arteries. If that supply drops, even for a few hours, the fibres at the nerve head swell and start to die.
That is NAION. The word "anterior" means the damage is at the front of the nerve, where it can be seen: on examination the disc looks swollen, often with small flame-shaped haemorrhages at its edge. "Non-arteritic" means the blood supply failed for vascular reasons such as low night-time blood pressure, a crowded disc or small-vessel disease, rather than from the inflamed arteries of giant cell arteritis.
Swelling inside a tight space makes things worse. A swollen nerve head compresses its own capillaries, which cuts blood flow further. Clinicians call this a compartment-syndrome-like effect, and it helps explain why some patients get worse over the first days or weeks before things settle.
NAION is a sudden drop in blood flow to the front of the optic nerve. It causes painless vision loss in one eye, often noticed on waking, usually as a missing upper or lower half of vision or a general dimming. It mostly affects people over 50 with a small, crowded optic disc and vascular risk factors such as high blood pressure, diabetes or sleep apnoea. No treatment has been shown to restore vision, but a meaningful minority improve on their own. The first priority is to rule out giant cell arteritis, which looks similar, threatens both eyes within days, and needs high-dose steroids straight away.
Section 02 — Interactive
The “disc at risk”:
why a small cup matters.
The best-established anatomical risk factor for NAION is a small optic disc with little or no central cup. All the fibres still have to pass through the opening, so a small disc packs them tightly. Move the cup-to-disc slider below and switch between a normal disc, the acute swelling of NAION, and the pale disc left weeks later.
A crowded disc is common, and most people who have one never get NAION. It is a predisposition, not a diagnosis. It does explain two things patients often ask about. First, why the other eye is at risk: disc anatomy tends to be similar in both eyes. Second, why glaucoma and NAION look so different, even though both damage the optic nerve. Glaucoma enlarges the cup over years, while the eye most prone to NAION usually starts with almost no cup at all.
Section 03 — The Emergency Look-Alike
Arteritic or not:
the question that
must be asked first.
Anterior ischemic optic neuropathy comes in two forms. The non-arteritic form accounts for the large majority, around nine in ten cases. The arteritic form is caused by giant cell arteritis (GCA), an inflammation of medium and large arteries in people over 50. It is less common and far more dangerous, because without treatment the second eye can be lost within days.
| Feature | Non-arteritic (NAION) | Arteritic (GCA) |
|---|---|---|
| Typical age | Usually 50s–70s, sometimes younger | Almost always over 50, more often over 70 |
| Symptoms beyond the eye | Usually none | New headache, scalp tenderness, jaw pain on chewing, weight loss, fever, shoulder and hip stiffness |
| Vision loss | Variable, often moderate | Often severe; brief episodes of blackout may come first |
| Disc appearance | Swollen, often hyperaemic; crowded disc in the fellow eye | Often chalky-white swelling; fellow eye cup can be normal |
| Blood tests | ESR and CRP usually normal | ESR and CRP usually raised; platelets may be high |
| Treatment | No proven therapy; manage risk factors | High-dose steroids started immediately, before biopsy results |
Section 04 — Who Gets It
Risk factors:
the disc, the vessels
and the night.
NAION is estimated to affect somewhere around 2 to 10 people per 100,000 over the age of 50 each year in Western populations. It rarely has a single cause. Usually several factors stack on top of a structurally crowded disc.
Other associations are reported, with weaker or debated evidence. They include certain medicines (phosphodiesterase-5 inhibitors such as sildenafil, and amiodarone), major blood loss or low blood pressure during surgery, and, rarely, the period after cataract or other eye surgery. None of these is a reason to stop a prescribed medicine on your own. Each is something to discuss with the prescribing doctor, especially if NAION has already affected one eye.
Section 05 — The Semaglutide Question
Ozempic, Wegovy
and the optic nerve:
what is actually known.
In 2024 a retrospective study from a single neuro-ophthalmology centre in Boston reported that patients prescribed semaglutide had a markedly higher hazard of NAION than matched patients on other drugs, both in people with type 2 diabetes and in people treated for overweight or obesity. Because these medicines are used so widely, the report drew a lot of attention.
Retrospective studies cannot prove cause, and later work using larger databases gave mixed results, with many finding a smaller increase or none. Regulators reviewed the evidence. In June 2025 the European Medicines Agency's Pharmacovigilance Risk Assessment Committee (PRAC) concluded that NAION is a very rare side effect of semaglutide, possibly affecting up to 1 in 10,000 people taking it, and recommended updating the product information.
Section 06 — The Evidence on Recovery
The trial that stopped
a surgery, and what
it taught us.
In the early 1990s, optic nerve sheath decompression (cutting a window in the sheath around the nerve to relieve pressure) was a popular treatment for NAION. The Ischemic Optic Neuropathy Decompression Trial (IONDT) randomised patients to surgery or careful follow-up. It was stopped early. The surgery did not help and appeared to cause harm.
Rounded proportions from the IONDT 6-month results (JAMA 1995). Bar lengths are approximate; see References for the primary source.
The trial left a second, more hopeful finding. Untreated, a substantial share of patients improved by themselves. Many people expect NAION to be permanent and complete, but central acuity often recovers partly, even when a band of field loss remains. Since the IONDT, steroids, drugs that lower clotting or improve blood flow, injections into the eye and neuroprotective agents have all been studied. None has yet shown clear, reproducible benefit in a high-quality randomised trial.
surgery (IONDT, 6 mo)
within ~5 years
swelling to resolve
Section 07 — What Happens Next
The work-up,
and protecting
the other eye.
NAION is a clinical diagnosis. It is built from the history, a dilated look at both optic discs, visual field testing and, increasingly, OCT of the nerve fibre layer. The work-up is about confirming the pattern, excluding mimics, and finding the risk factors that can still be changed.
| Step | Why it is done |
|---|---|
| ESR, CRP, full blood count (over-50s) | Screen for giant cell arteritis on the same day |
| Visual fields and OCT | Map the defect, and track swelling and later nerve fibre loss |
| Blood pressure, glucose, lipids | Find and treat vascular risk factors |
| Sleep apnoea assessment | Common, treatable, and strongly associated with NAION |
| Medication review | Look at the timing of blood pressure tablets and at drugs with reported associations, together with the prescriber |
| MRI (selected cases) | If pain, younger age, progression or atypical features suggest optic neuritis, compression or another cause |
A man with treated hypertension and loud snoring notices on waking that the lower half of his right eye's vision looks "shaded". There is no pain or headache. The doctor finds a swollen right disc with a small haemorrhage, and the left disc is small with almost no cup. ESR and CRP are normal. The diagnosis is NAION. Nothing reverses it, but a sleep study shows significant obstructive sleep apnoea, and his evening blood pressure dose is reviewed with his physician. At three months his acuity has improved by two lines. The lower field defect remains, and the aim now is to protect the left eye.
Living with NAION usually means adjusting rather than losing function. With one good eye, most people keep reading and, depending on local rules, driving. Field loss in the lower half can make stairs and kerbs harder. Low-vision services and a simple habit of scanning downward help. The most important long-term step is the unglamorous one: controlling the vascular and sleep risks that put the second eye in the same position.
Section 08 — FAQ
Frequently asked questions
about NAION.
Non-arteritic anterior ischemic optic neuropathy (NAION) is a sudden loss of blood supply to the front of the optic nerve, where it enters the eye. The nerve head swells, nerve fibres are damaged, and vision drops in one eye, usually without pain and often noticed on waking. It is the most common acute optic neuropathy in people over 50. 'Non-arteritic' means it is not caused by inflammation of the arteries, which separates it from the giant cell arteritis form.
People often call it a stroke of the optic nerve, and the comparison is fair in that blood flow fails and tissue is damaged. It is not the same as a central retinal artery occlusion, which blocks the main artery of the retina itself and is treated as a stroke emergency. Both need same-day assessment, because telling them apart, and ruling out giant cell arteritis, decides what happens next.
Some does. In the Ischemic Optic Neuropathy Decompression Trial, roughly four in ten patients who were simply observed had improved by three or more lines of acuity at six months. Much of the visual field loss, often a band missing from the lower or upper half of vision, tends to remain. The swelling settles over about six to eight weeks and leaves a paler disc behind.
A link has been reported and taken seriously. A 2024 retrospective study from one US centre found a higher NAION risk in patients prescribed semaglutide, and later studies gave mixed and generally smaller estimates. In 2025 the European Medicines Agency's safety committee concluded that NAION is a very rare side effect of semaglutide, affecting up to about 1 in 10,000 users. Anyone on these drugs who notices sudden vision loss should stop and see an eye doctor urgently, and should not stop or change the medicine without speaking to their prescriber.
It can be. In the long-term follow-up of the decompression trial cohort, about 15 percent of patients developed NAION in the second eye within five years. Because the crowded optic disc that predisposes to NAION is usually present in both eyes, managing risk factors such as sleep apnoea, blood pressure and diabetes matters for protecting the fellow eye.
There is no proven treatment that restores vision. Optic nerve sheath decompression surgery was tested in a randomised trial in the 1990s and was stopped early because it did not help and may have caused harm. Steroids and other drugs have been studied without clear benefit. Care focuses on ruling out giant cell arteritis, which is treatable and urgent, and on reducing vascular risk factors to protect the other eye.
References & Evidence Base
Peer-reviewed
citations.
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