blurred vision after smoking weed

Smoking Weed Regularly May Cause Vision Problems

New research suggests that weed could mess up your vision beyond just bloodshot eyes.

Published in JAMA Ophthalmology this week, a 52-person study explores how pot might influence the function of the user’s retinal ganglion cells, or the nerve cells just behind the surface of the retina that transmit information back to the brain to create a visual image.

“We showed an association between regular cannabis use and a delay in the visual processing,” researcher Vincent Laprévote, M.D., Ph.D., from the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy, Laxou, France, told Motherboard. “Our hypothesis is that regular cannabis use could slow down the transmission between retinal neural cells.”

The researchers found a delay in the transmission of action potentials, or neural signals, from the retina back to the brain—a result which ultimately could lead to a change in vision. Laprévote said it’s a long-term effect, since participants had to stop their consumption before the tests. On average, they’d been using cannabis for six years. Whether this effect has behavioral consequences, the researchers have yet to find out, he said.

“Our findings may be important from a public health perspective since they could highlight the neurotoxic effects of cannabis use on the central nervous system as a result of how it affects retinal processing,” the researchers wrote. Overall, this might indicate brain neurotransmission abnormalities in cannabis users.

To conduct their study, Laprévote and his colleagues used a standard electrophysiological measurement known as “pattern electroretinography (PERG).” An electroretinogram is a test that evaluates electrical activity among neural and non-neuronal retinal cells in response to light.

Of the study’s participants, 28 used cannabis regularly, while the other 24 functioned as controls. The researchers found that the pattern electroretinography took longer in regular cannabis users: a median of 98.6 milliseconds, as compared with 88.4 milliseconds for the controls.

With that said, though cannabis use may cause red eye upon getting stoned, it’s been proven helpful with eye issues like glaucoma, and to even make regular users better drivers than otherwise—which of course entails proper vision. Among glaucoma patients, cannabis helps alleviate the pressure they feel in their eyes, which otherwise causes damage to the optic nerve and potential vision loss.

So whatever the overall implications may be in regard to this study and cannabis’ effects on vision, as legalization sweeps the country, it’s important to conduct more research to get to the bottom of how smoking pot influences eyesight.

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Does Marijuana Use Affect a Person’s Vision?

Regular marijuana use may affect how well certain cells in the eye’s retina function, a small new study finds.

But some experts say that the evidence presented in the study isn’t strong enough to support the link between these two factors. The cells that the researchers focused on in the study, called retinal ganglion cells, are located near the inner surface of the eye’s retina. These cells collect visual information and transmit it to the brain.

The study included 52 people who had used marijuana at least 7 times per week during the previous month and 24 people who had never used marijuana. The people in both groups were between 18 and 35 years old. The researchers verified the marijuana use by testing the people’s urine for THC, marijuana’s main psychoactive ingredient. [7 Ways Marijuana May Affect the Brain]

The researchers tested the participants’ vision and found that their eyesight was relatively good, and that no one in the study group reported having any visual problems from using marijuana such as blurred vision, according to the study, which was published today (Dec. 8) in the journal JAMA Ophthalmology.

To study how well the participants’ retinal ganglion cells worked, the researchers used a method called pattern electroretinography, which provides information about how well those cells function, as well as how fast they transmit visual information from the retina to the brain.

The test revealed that, compared to the people who didn’t use marijuana, those who did use the drug had a slight delay in how long it took for information to be transmitted from the retina to the brain, according to the study.

It’s not clear whether this potential effect of marijuana is permanent, or would stop when a person stops using the drug, said study co-author Dr. Vincent Laprévote, a psychiatrist at Pôle Hospitalo-Universitaire de Psychiatrie du Grand Nancy in France.

But some experts argue that the study had significant limitations, and because of this, it’s unclear whether or not there is an actual link between marijuana use and these effects.

More research is needed to determine whether marijuana use really is linked to changes in the functioning of those cells, said Dr. Christopher J. Lyons, an ophthalmologist at the University of British Columbia, who was not involved in the study. [Marijuana Could Treat These 5 Conditions]

Lyons noted that although the electroretinography results suggested a difference between marijuana users and nonusers, the delay didn’t seem to translate into actual problems with the users’ vision.

Indeed, the marijuana users in the study did not experience any actual visual symptoms or changes in the quality of their vision, Lyons told Live Science.

In an editorial that was published in the same journal as the study, Lyons and Dr. Anthony Robson, an ophthalmologist at the University College London who was also not involved in the study, noted that the researchers examined the people’s marijuana use through urine tests, which are not as accurate as blood tests.

In addition, there are many other factors such as tobacco use, diet and lifestyle that might affect the functioning of a person’s retinal cells, and these factors could have affected the results of the study, Lyons and Robson wrote.

Moreover, while the study authors said that the abnormalities that they found in the study that involved the functioning of the marijuana users’ retinal ganglion cells might explain why some marijuana users experience altered vision, they did not present any evidence in the study to support this statement.

Regular marijuana use may affect how well certain cells in the eye work, a small new study finds.