What is NAION?

NAION (Non-Arteritic Anterior Ischemic Optic Neuropathy) is a condition in which blood flow to the front part of the optic nerve is compromised, causing sudden, painless vision loss in one eye.
The vision loss is often irreversible, and there is no proven effective therapy to reverse it.
According to the American Academy of Ophthalmology, the incidence of NAION is 0.05 per 10,000 across all age groups, but it increases to between 0.23 and 1.02 per 10,000 individuals who are over the age of 50.
In addition to age, risk factors for NAION include systemic vascular disease (e.g. hypertension, diabetes), small “crowded” optic discs (so-called “disc at risk”), sleep apnea, hypotensive episodes, smoking, hypercholesterolemia.
A “disc at risk” is not a disease, but an anatomic variant.
A "disc at risk" refers to a small, crowded optic disc with a small cup-to-disc ratio (typically ≤ 0.2). Because there’s little space for nerves and capillaries, even a small reduction in perfusion can cause ischemic damage to the optic nerve head — predisposing to NAION.
Multiple studies confirm that in ~ 95% of NAION cases, the patient has a "disc at risk".
Having a “disc at risk” is a major predisposing factor — but not sufficient alone; systemic and vascular factors usually trigger the event.
It is estimated that ~10–20% of the general population has this "disc at risk" anatomy, and are thus theoretically predisposed.

Evidence of association with Ozempic / Semaglutide?

In June 2025, WHO issued a safety alert noting a potential increased risk of NAION with semaglutide-containing medications (Ozempic, Rybelsus, Wegovy).
A large retrospective cohort study (3,344,205 patients with diabetes) compared semaglutide users with non-users and found that semaglutide was associated with a higher hazard of NAION at 2, 3, and 4 years.
Some studies reported a 3-4 fold increased risk of NAION in semaglutide users vs non-users, whilst other studies showed no increased association at all.
No studies suggest any causation.

Magnitude of risk & rarity

Some professional societies (e.g. American Academy of Ophthalmology) caution that the evidence is limited and that causality has not been established; they emphasise that the baseline risk is low.
Baseline annual risk of NAION (no semaglutide, overall population): ~ 0.2 - 1.0 in 10,000.
Estimated risk on semaglutide: somewhere around ~ 0.4 - 3.0 in 10,000.
So, absolute increase ~ 0.2 - 2.0 extra NAION case per 10,000 users per year.

To put things into context, healthy individuals have a higher chance of actually dying from these procedures:

Mechanistic hypotheses & uncertainties

It is unclear whether semaglutide directly leads to NAION, or whether the association is indirect (e.g. through changes in blood pressure, vascular flow, or rapid improvements in glucose control altering perfusion).
The possibility exists that people already predisposed (e.g. with other vascular risk factors such as hypertension or diabetes or "disc at risk") are more vulnerable.

Clinical implications & recommendations

Patients on semaglutide (Ozempic) should be made aware of this rare risk, especially if they have underlying risk factors for optic nerve ischemia.
If a patient experiences sudden vision loss or rapidly worsening vision while using semaglutide, they should immediately seek evaluation by an ophthalmologist or neuro-ophthalmologist. Regulatory guidelines recommend discontinuing semaglutide if NAION is confirmed.
In the context of medications such as semaglutide (Ozempic/Wegovy), knowing if a patient has a "disc at risk" anatomy can help in risk counselling — though no screening guideline currently mandates optic disc examination prior to starting therapy.
"Disc at risk" is typically identified during optometric or ophthalmologic examination using OCT imaging.
If a patient intends to use Ozempic/Wegovy/Mounjaro, I would recommend seeing an optometrist for optical coherence tomography (OCT).
If OCT confirms normal anatomy, then the risk of NAION becomes virtually the same as someone not taking semaglutide.
This test (+/- a comprehensive eye examination) usually costs ~ $80 - $150.
Most optometrists should offer this service.

Optometrists in the Melbourne CBD offering OCT Imaging (there may be others)

Eyes on Optometrists

Shop 2, 185-191 Queen St, Melbourne 3000

Phone: 03 9600 3888

Email: queenstreet@eyeson.com.au

Hours: Mon to Fri: 9.00am to 5.00pm

Collins St Optometrists

Level 9, 267 Collins St Melbourne, 3000

Clinic Hours - Monday - Friday 9AM - 6PM