Some research suggests that GLP-1 medications may elevate the risk of a rare form of vision loss, though that link has not been proven in a rigorous study

Several studies have suggested that Ozempic and other GLP-1s may raise the risk of non-arteritic anterior ischemic optic neuropathy, a rare eye condition that can cause partial or full vision loss. (Photo illustration by Mario Tama/Getty Images)

A routine eye exam could help the millions of Americans taking GLP-1s better understand if they are at risk for a rare form of vision loss.

As part of a routine eye exam, ophthalmologists assess the eye's cup-to-disc ratio. It takes about 10 minutes.

Having a low cup-to-disc ratio is one risk factor for non-arteritic anterior ischemic optic neuropathy (NAION), an optic-nerve injury that typically occurs in people older than 50 and causes partial or full vision loss.

There are several risk factors for NAION, including a chronic condition like Type 2 diabetes or high blood pressure, or being born with a small optic disc. The condition is painless but occurs quickly - often within hours or days - and is sometimes described as an "eye stroke" that can occur after a rapid improvement in blood glucose.

A growing body of research suggests that GLP-1 medications like Novo Nordisk's (NVO) (DK:NOVO.B) Ozempic or Eli Lilly's (LLY) Mounjaro may elevate the risk of NAION, though that link has not been proven in a rigorous study. Dozens of patients who experienced NAION after starting a GLP-1 drug are suing Novo and Lilly, according to a Wall Street Journal report last week that was widely picked up.

It's one of the first possible side effects associated with the popular medications that seems to give some patients pause.

The American Academy of Ophthalmology doesn't recommend that patients seek out an eye exam before starting treatment with a GLP-1. However, some are already doing so. "I have had patients come to me to check their cup-to-disk ratios in light of the new data," Melinda Hakim, an ophthalmologist in Los Angeles, said in an email.

Benefits of GLP-1s outweigh the risk, doctors say

Some physicians who prescribe GLP-1s say that the benefits of these medications, whether that's weight loss, lower blood glucose or improved cardiovascular health, still outweigh the risks of NAION for most Americans. The risk for NAION may be as low as 0.1%.

"The average person that comes to see me - if they're stacked with all these risks for heart disease, I wouldn't hold back a medication for such a low risk," Sun Kim, an endocrinologist at the Stanford Health Care system, said in an interview.

Kim is the co-author of a study published earlier this year in JAMA Ophthalmology that detected a twofold increase in NAION risk in U.S. veterans with Type 2 diabetes who had started taking semaglutide. She described the vets in the study as older and sicker than the general public.

It's one of several studies that have detected a signal between GLP-1s and NAION, starting with one in 2024 that found a possible link between NAION and semaglutide. Kim noted that semaglutide - the active ingredient in Ozempic and Wegovy - is more common in these studies because those drugs have been on the market longer than Lilly's Mounjaro and Zepbound.

But not all research has found such a link. A study published last year examined the medical records of 260,000 people with diabetes in the U.S. and found no correlation between taking semaglutide and having NAION after five years. Novo's investigation of its own clinical trials for semaglutide and an older GLP-1 drug called liraglutide did not find an increase in the risk of NAION in patients with diabetes or obesity.

"A causal relationship between GLP-1 [receptor agonists], including semaglutide, and NAION cannot be confirmed based on the totality of data," a Novo spokesperson said in a statement.

In Europe, the label for Novo's Ozempic, Rybelsus and Wegovy lists NAION as a "very rare" side effect affecting 1 in 10,000 people taking the medication. The medications' labels in the U.S. do not list NAION as a side effect.

"We will continue to review data, including any data regarding ophthalmic issues," a Lilly spokesperson said.

For patients worried about the risk of NAION, there are a few things to consider. They can get their cup-to-disc ratio checked. If someone has diabetes, they should be getting a routine diabetic eye exam regardless. And for patients who have already experienced NAION, which usually occurs in one eye, Kim suggests talking to their doctor before starting a GLP-1.

"There may be a doubling of a very, very low risk," she said, "but I think the benefits here completely outweigh [the risks] for most people."

-Jaimy Lee