Semaglutide, Ozempic and Wegovy: The NAION Eyesight Warning

Their effect on eyesight has now become an urgent and uncomfortable issue.

Medicines developed to treat diabetes have become central to a worldwide weight-loss trend. Two recent studies have brought a potential eyesight warning into sharper focus, injecting caution into what had seemed an almost too-good-to-be-true story.

What the latest studies found

Semaglutide, marketed as Ozempic, Wegovy and Rybelsus, is part of the GLP-1 drug class. It helps regulate blood glucose and suppresses appetite. Weight falls, while cardiometabolic risk improves. However, ophthalmology specialists warn that the optic nerve may not benefit in the same way.

A Massachusetts Eye and Ear team reviewed medical records spanning 2017 to 2023. It compared people with diabetes or obesity who were taking semaglutide with comparable patients who were not. Published in JAMA Ophthalmology in July 2024, the results found more cases of the uncommon eye condition non-arteritic anterior ischaemic optic neuropathy, or NAION, among people exposed to the medicine. Relative risk increased by around fourfold for people with diabetes and by more than sevenfold for people with obesity using semaglutide. Absolute case numbers were still low, but the finding was strong enough to prompt concern.

A separate cohort study from the Karolinska Institutet and the University of Melbourne identified a very small absolute risk - around 0.04% of the patients examined - although this was still marginally above that of matched controls. Both research groups urge caution in interpreting the findings: diabetes itself increases NAION risk, complicating any claim of a direct causal relationship. A 2013 PLOS ONE meta-analysis had already associated diabetes with a 64% increased risk of NAION, well before weight-loss injections made headlines.

NAION is rare. The association with semaglutide looks small in absolute terms, but not trivial for people who already carry eye or vascular risk.

How NAION affects vision

NAION is occasionally described as a “stroke of the eye”. Blood flow to the optic nerve head suddenly becomes impaired. Sight in one eye may darken, frequently upon waking. It is generally painless, and the resulting damage may be permanent. Ophthalmologists pay particular attention to patients with a so-called “crowded” optic disc, high blood pressure, sleep apnoea or previous vascular disease. These characteristics appear to create the conditions for greater susceptibility.

• Common warning signs: a sudden dark patch, a curtain in the visual field, washed-out colours, or rapid blurring in one eye.
• Higher-risk profiles: diabetes, obesity, hypertension, sleep apnoea, a crowded optic disc, previous NAION in the other eye.
• Immediate steps: stop the injection, seek urgent eye assessment, and tell the clinician about your GLP-1 treatment.

If vision turns dim or patchy after a jab, treat it as an emergency. Act fast and get the eye examined the same day.

How regulators and clinicians are responding

Europe has acted on the emerging signal. In June 2025, the European Medicines Agency classified NAION as a “very rare” adverse effect of semaglutide and recommended stopping treatment if sudden visual symptoms occur. The update does not prohibit the drug; instead, it changes how informed consent and monitoring should be approached.

Clinicians must now strike a familiar balance. GLP-1 medicines promote weight reduction, improve glucose management and reduce cardiovascular risk. For many patients, these benefits outweigh the risk of an exceptionally uncommon eye event by a considerable margin. Individual risk, though, is not uniform. Those with sleep apnoea, uncontrolled blood pressure or a history of optic nerve problems may require more intensive follow-up. Shared decision-making is central, alongside clear guidance on symptoms that need attention.

What this means for people taking Ozempic or Wegovy

There is no need to panic. For any individual, the likelihood of NAION remains low. Do not discontinue medication before discussing it with your GP or specialist. If you are beginning a GLP-1 medicine and have additional risk factors, arrange an eye examination. Tell your clinician about sleep apnoea, blood pressure concerns and any past optic nerve issues. Ask them to record your baseline vision and optic disc appearance, as this information can be useful if symptoms develop later.

Keep a visual symptom diary while your dose is being increased. Record dark spots, visual-field changes or altered colour perception, and report them without delay. Keep blood pressure well controlled and seek treatment for sleep apnoea where needed. Remain well hydrated, particularly if injection-related nausea means you are drinking less. Such straightforward measures help support blood supply to the optic nerve.

Why the optic nerve may be at risk

Researchers are investigating several possible explanations. One concerns microcirculation in the optic nerve head, where alternative blood-flow routes are limited. Fast changes in glucose levels, blood pressure or vascular tone may push an already vulnerable nerve into ischaemia. Another theory concerns anatomy: a cramped optic disc has less capacity for swelling, increasing the likelihood of a mismatch between pressure and perfusion. GLP-1 receptors could also alter vascular reactivity in ways that are not yet fully understood.

Longer-term research is underway. One current project is following approximately 1,500 patients for five years, using retinal scans, assessments of optic nerve structure and records of events alongside dose adjustments and metabolic changes. Its aim is straightforward: determine who is at greater risk, when that risk is greatest and which protective measures are effective.

The next phase is precision. Pin down the small group at risk and keep the wider pool on treatment with eyes wide open.

Making decisions using real-world numbers

Absolute risk is important when considering treatment choices. A figure of 0.04% means that four out of 10,000 treated people developed NAION in one analysis. The overwhelming majority of patients will not experience it. Yet the consequences can be serious when vision is affected. This is why care will be personalised. A person with obesity, hypertension and sleep apnoea could gain substantial cardiovascular benefits from semaglutide, while also needing closer eye monitoring.

Practical steps before and during treatment

• Ask for a baseline eye examination, including optic disc photographs, if you have vascular risk factors.
• Agree a symptom plan: what action to take, who to contact and when to pause doses.
• Check blood pressure, particularly overnight if your doctor suspects drops that could deprive the optic nerve of blood.
• Keep glucose changes gradual during dose escalation; discuss the pace if you feel unwell or dehydrated.
• Report any vision change in one eye immediately, even if it has eased by midday.

A few definitions can be useful when discussing treatment with a clinician. GLP-1 means glucagon-like peptide-1, a gut hormone that stimulates insulin release and slows gastric emptying. Semaglutide is a GLP-1 agonist. NAION is an ischaemic injury affecting the front section of the optic nerve without arterial inflammation. It differs from diabetic retinopathy, which involves the blood vessels of the retina and commonly progresses over time.

Alternatives are available if semaglutide is not appropriate. There are other GLP-1 medicines as well as non-GLP-1 weight-loss treatments, each with a different balance of risks and benefits. People who have previously experienced NAION in one eye have a greater risk in the other and will require an individualised plan. The same applies to workers who depend on flawless vision, including pilots, surgeons and electricians.

The message is not a judgement against weight-loss injections. It is an argument for using them precisely. GLP-1 therapy continues to offer major benefits to many people. The eye warning is uncommon but genuine. Discuss risks early, arrange monitoring and respond quickly to any symptoms. This allows patients to retain the advantages of modern obesity care while safeguarding their most irreplaceable sense.