The phrase “eye stroke” has recently surfaced in news reports as a rare side-effect of weight-loss injections, sparking widespread concern. This term, although not a formal medical diagnosis, is used to describe a condition where reduced blood flow damages the optic nerve, leading to sudden vision loss. Unlike a conventional stroke, which can result in loss of limb movement or speech, an eye stroke may initially be harder to recognize. Vision can be lost entirely or partially, in one or both eyes, without the accompanying numbness or paralysis.
The use of the word “stroke” is due to the similarity in underlying causes: a loss of blood supply leading to cell death and tissue damage. The medical term for an eye stroke is non-arteritic anterior ischemic optic neuropathy (Naion). The recent connection between Naion and weight-loss treatments has made headlines following a large study examining semaglutide, the active ingredient in several popular weight-loss drugs.
Semaglutide and Its Implications
Researchers analyzed over 30 million side-effects reported to the US Food and Drug Administration and found that 31,774 involved semaglutide. One drug in particular, Wegovy, was found to have a significantly stronger association with Naion compared to other semaglutide-based treatments. The study suggested that the risk of eye stroke from Wegovy was almost five times greater than from Ozempic, despite Wegovy being linked to fewer overall reported side-effects.
Understanding why semaglutide might reduce blood flow to the eye requires some background. Semaglutide is a synthetic version of a naturally occurring hormone called GLP-1, which helps regulate blood sugar by stimulating insulin production, reducing the release of glucagon, and slowing digestion. It has been used to treat type 2 diabetes, heart disease, and obesity. Wegovy is administered by injection at a higher maximum dose than Ozempic, another injectable medication. Notably, no link was found between Naion and Rybelsus, the tablet form of semaglutide.
The Role of Dosage and Administration
The speed at which Wegovy causes weight loss—faster than other treatments—may itself be part of the explanation. The human body is a finely balanced system, and the autonomic nervous system, which controls involuntary functions like heart rate and digestion, relies on a careful balance of hormones. When an external drug significantly alters how these hormones behave, it can affect the body in unexpected ways.
The relatively high doses used with Wegovy may cause blood pressure to fluctuate beyond normal ranges. A notable drop in blood pressure reduces the rate at which blood flows through the body, and the eye is particularly vulnerable to this. The retina, served by some of the tiniest blood vessels in the body, depends on these small vessels for its oxygen supply. Any significant change in blood pressure can seriously disrupt this delicate circulation.
Gender Disparities and Risk Factors
This does not, however, fully explain why a drug that is broadly beneficial for heart health and blood sugar control might have such a specific harmful effect on eyesight. Nor does it explain another surprising finding from the study: men taking these weight-loss treatments appeared to face three times the risk of vision loss compared to women.
The study did not provide enough detail about the differences between male and female participants, such as whether more severely obese men than women were included. Large-scale data of this kind does not always capture the finer details needed to fully understand cause and effect. It is important to keep all this in perspective: while a link between semaglutide and vision loss has been identified, this side-effect remains rare.
Future Research and Safety Measures
More research is needed to establish safe dosage levels and to understand whether certain factors—such as sex, age, weight, or existing health conditions—make some people more vulnerable than others. Semaglutide is being prescribed for a growing range of conditions and increasingly to younger patients. To ensure that these treatments do not lead to life-changing sight loss, properly designed clinical trials that assess the level of risk are essential.
A spokesperson for Novo Nordisk told the Guardian: “Patient safety is our top priority, and we take any reports about adverse events from the use of our medicines very seriously. We work closely with authorities and regulatory bodies from around the world to continuously monitor the safety profile of our products.”
The EU patient leaflets for Wegovy, Ozempic, and Rybelsus have been updated to include Naion, they added, but “based on the totality of evidence, we concluded that the data did not suggest a reasonable possibility of a causal relationship between semaglutide and Naion and Novo Nordisk believes that the benefit-risk profile of semaglutide remains favourable.”
As the conversation around weight-loss injections and their side effects continues, the medical community and patients alike await further research to clarify these risks and ensure the safe use of these treatments.
