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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