A new study suggests poppers may cause serious and permanent eye damage. A report in The British Journal of Ophthalmology found that the inhalants, often used as a sexual aide by gay men, were connected to retinal damage in a number of men.

Poppers, which expand blood vessels and loosen involuntary muscles, have long been used by gay men to facilitate anal sex. But in 2006 a key ingredient, isobutyl nitrite was classified as a cancer-causing agent and replaced with isopropyl nitrite. It's believed isopropyl nitrite damages the fovea, the portion of the retina responsible for central vision.

The study profiled 12 men who reported vision trouble within hours or days of inhaling poppers, most commonly blurriness or blind spots. Researchers examined the chemical makeup of the brands the men reported using, and found they all had isopropyl nitrite.

"The mounting body of evidence [suggests] that poppers can have serious effects on central vision," said lead researcher Dr. Rebecca Rewbury, adding that many "users and health care professionals may be unaware of the risk."

There is still more research to be done, however: Most of the subjects recovered their vision fully, but not all did. And without clear regulations, it's hard to determine which brands contain isopropyl nitrite, and in what quantities.

It's not the first time poppers have have been associated with vision problems, though: In 2010, a letter to The New England Journal of Medicine outlined several sudden cases of vision loss by patients who had used them.

In 2015, lawmakers in Britain attempted to add poppers to a broad ban of so-called "legal highs" like nitrous oxide and synthetic cannabis. The controversy led to one Conservative Party MP outing himself as a poppers user, and the substance was eventually left off the ban.