Inhaling the vapors from "poppers" to get high even once can cause eye damage, but habitual huffing may lead to months-long vision loss, French doctors say.

The study was small, only involving six HIV-positive men with a history of other drug use. The men had been using poppers at least once a week for months or years before going to see eye doctors because of vision problems in both eyes.

In the men who kept using poppers, visual disturbances continued, co-author Dr. Michel Paques from the Quinze-Vingts Hospital in Paris told Reuters Health by email.

In men who stopped, vision improved after several months - but Paques and his colleagues aren't sure whether that will always be the case.

Poppers are small vials of a type of chemical called alkyl nitrates that are crushed or "popped" to release the fumes. These compounds give off nitric oxide, which produces a quick, short-lived high.

The men in the study all had damage to the retina -- the part of the eye that detects light. The severity of the damage was not linked to how long the men were using the poppers, Paques said.

Last October, writing about a different set of patients, Paques and colleagues reported in The New England Journal of Medicine that just a single use of poppers can damage vision. (See Reuters story of October 13, 2010, at reut.rs/eEajjr.) Even though the compound that produces the high doesn't stay in the body for very long, "its effects remain for months," Paques told Reuters Health. Animal studies have shown the compound is involved in vision, but researchers don't know the effect of large doses, Paques said.

Some of the men in this study already suspected the poppers were to blame when they went to the eye doctors. In all cases, doctors advised them to stop using poppers - and those who did saw their vision improve after a few months.

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