The word “eyebrow” has been in the news recently about a very rare side effect of weight loss injections. It is not an official medical diagnosis, but an acronym used to describe a condition in which reduced blood flow damages the optic nerve and causes sudden vision loss.
The phrase may be misleading. Unlike a traditional stroke — which can cause a person to lose the ability to move their limbs or speak — an eye stroke can be hard to recognize at first. Vision can be completely or partially lost, in one or both eyes, without numbness or paralysis.
The word “stroke” is used because with the more familiar condition, the main cause is a loss of blood supply that leads to cell death and tissue damage. The correct medical term for eye stroke is non-arterial anterior ischemic optic neuropathy (NAION).
A recent link between nine and weight loss treatments made headlines after a large study examining semaglutide, the active ingredient in many popular weight loss medications.
Researchers analyzed more than 30 million side effects reported to the US Food and Drug Administration and found that 31,774 involved semaglutide. One drug in particular stood out: Vigovi had a stronger relationship with Nine than other semaglutide-based treatments.
The study suggested that the risk of eye attack from Vigoi was nearly five times greater than that from Ozympic, although Vigoi was associated with fewer reported side effects.
Understanding why semaglutide may decrease blood flow to the eye requires a little background. Semaglutide is a synthetic version of a natural hormone called GLP-1, which helps regulate blood sugar. It stimulates insulin production, reduces the release of a sugar-raising hormone called glucagon, and slows digestion.
Semaglutide is used to treat type 2 diabetes, heart disease, and obesity. Vigovi is administered by injection at a higher maximum dose than Ozympic, another injectable drug. Injected drugs enter the bloodstream faster and in greater concentration than tablets – and significantly no relationship was found between Nien and Rebelsus, the tablet form of semaglutide.
The speed with which Vigovi causes weight loss—faster than other treatments—may itself be part of the explanation. The human body is a perfectly balanced system in which no organ or process works in isolation.
The autonomic nervous system, which controls involuntary functions such as heart rate and digestion, relies on a careful balance of hormones to keep things in check. When an external drug significantly changes how these hormones behave, it can affect the rest of the body in unexpected ways.
Relatively high doses used with Vigovi may cause blood pressure to fluctuate outside the normal range. A significant drop in blood pressure reduces blood flow through the body, and the eyes are particularly vulnerable to this.
The retina is served by small blood vessels everywhere in the body, and it depends on these small vessels for oxygen supply. Any significant change in blood pressure can seriously disrupt this delicate flow.
Men are at a much higher risk than women
However, this does not fully explain why a drug that is widely beneficial for heart health and blood sugar control may have such a particularly harmful effect on eyesight. Nor does it explain the study’s other surprising finding: Men taking these weight-loss drugs are three times more likely to lose vision than women.
The study did not fully explain the differences between male and female participants. For example, whether there were more severely obese men than women. Furthermore, such large-scale data do not always capture the detail necessary to fully understand cause and effect.
It’s important to keep all of this in perspective: while a link between semaglutide and vision loss has been identified, this side effect remains rare.
More research is needed to establish safe intake levels and to understand whether certain factors—such as gender, age, weight, or existing health conditions—make some people more vulnerable than others.
Semaglutide is being prescribed for a growing number of conditions and increasingly in younger patients. To ensure that these treatments do not cause life-changing vision loss, well-designed clinical trials that assess risk are essential.
RELATED: Risk of sudden vision loss nearly 5x higher with Vigoi than Ozympic, study finds
A spokesperson for Novo Nordisk told The Guardian: “Patient safety is our priority and we take any reports of adverse events from the use of our medicines very seriously. We work closely with authorities and regulatory bodies around the world to continuously monitor the safety profile of our products.”
The EU patient leaflets for Vigovi, Ozympic and Rebelsis were updated to include Naion, they added, but “based on all the evidence, we conclude that the data do not suggest a reasonable likelihood of a causal relationship between semaglutide and Naion and Novo Nordisk believes that the benefit-risk profile remains”.
Barbara Pircionek, Professor and Vice-Chancellor, Research and Innovation, Anglia Ruskin University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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