Study examines potential effect of regular marijuana use on vision

December 8, 2016
A dried flower bud of the Cannabis plant. Credit: Public Domain

A small, preliminary study has found an abnormality involving the retina that may account for altered vision in regular cannabis users. The results are published online by JAMA Ophthalmology.

Vincent Laprevote, M.D., Ph.D., of the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy, Laxou, France, and colleagues examined whether the regular use of cannabis could alter the function of (RGCs), which are the last and most integrated stage of retinal processing and the first retinal stage providing visual information in the form of , such as is found in the brain. Because cannabis is known to act on central neurotransmission, studying the retinal ganglion cells in individuals who regularly use cannabis is of interest.

To verify if cannabis disturbs RGC function in humans, the researchers used a standard electrophysiological measurement called pattern electroretinography (PERG), which involved averaging a high number of responses, thereby ensuring reproducibility of the results. With PERG, the best marker of RGC function is a negative wave—the N95 wave—2 parameters of which are usually known as the amplitude and the implicit time, which denotes the time needed to reach the maximal amplitude of N95.

Twenty-eight of the 52 study participants were regular , and the remaining 24 were controls. After adjustment for the number of years of education and alcohol use, there was a significant increase for cannabis users of the N95 implicit time on results of pattern electroretinography (median, 98.6 milliseconds, compared with controls, 88.4 milliseconds).

"This finding provides evidence for a delay of approximately 10 milliseconds in the transmission of action potentials evoked by the RGCs. As this signal is transmitted along the visual pathway via the optic nerve and lateral geniculate nucleus [a relay center in the thalamus for the visual pathway] to the visual cortex, this anomaly might account for altered vision in regular cannabis users," the authors write. "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."

"Independent of debates about its legalization, it is necessary to gain more knowledge about the different effects of cannabis so that the public can be informed. Future studies may shed light on the potential consequences of these retinal dysfunctions for visual cortical processing and whether these dysfunctions are permanent or disappear after cannabis withdrawal."

Explore further: Do cannabis users think package warnings are needed?

More information: JAMA Ophthalmol. Published online December 8, 2016.DOI: 10.1001/jamaophthalmol.2016.4761

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5 / 5 (1) Dec 08, 2016
On the other hand, cannabis has been shown to improve night vision. (See "Cannabis improves night vision: a case study of dark adaptometry and scotopic sensitivity in kif smokers of the Rif mountains of northern Morocco" - PubMed.)

Also if a mother-to-be uses alcohol during pregnancy, also using cannabis will help to prevent some of the vision problems that infants with fetal alcohol syndrome display! (See "Marijuana influences visual development" - Scoop.)

And it has been well known for decades that cannabis can treat glaucoma! (Run a search on "Elvy Musikka", she's a sweet old lady with glaucoma who uses cannabis.)
not rated yet Dec 08, 2016
what exactly do drugs like xanax and prozac and buspar and serzone and paxil and and and do to a persons vision capabilities?


not rated yet Dec 08, 2016
This Medical Express site HAS to be owned by pharmaceutical companies. They pull some of the most inane "studies" of Cannabis and not one yet has been real. I like how to study cannabis effects on vision they had to adjust for education level. The one constant medicinal use for weed has been glaucoma, isn't that eye sight related? They are pulling anything they can out of the ol' wazoo to try to discredit cannabis use, it is pathetic.
not rated yet Dec 09, 2016
What does " After adjustment for the number of years of education and alcohol use" even mean? Because it makes it sound like they adjusted the numbers to make the results they wanted, instead of using unaltered evidence.

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