Smokers Beware: Cannabis Can Damage Link between Retina and Brain


Researchers from the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy in France have found that regular cannabis use could damage eyesight.

The study conducted in France has found prolonged marijuana use could wear down retinal ganglion cells, the nerves that sit just behind the retina.

According to the research published on DailyMailOnline, it showed that previous studies have noted that cannabis helps patients with glaucoma, while the new study negated the earlier research,it  found regular users had a delay in processing visuals – even after quitting.

But the study found people who smoked weed for around six years experienced a delay in neural signals to the brain – even after giving up the drug.

The finding complicates scientific understanding on the link between cannabis and vision, since previous studies have shown the drug helps patients with glaucoma, and even improves night vision.

According to the lead author, ‘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,’ lead investigator Dr Vincent Laprevote, of the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy in France, said.

‘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.’

The small study involved 52 participants – 28 cannabis users, 24 never users.

All of the cannabis users stopped consuming the drug before the trial started, but had been regularly using it for at least six years.

The researchers used a standard electrophysiological measurement called pattern electroretinography (PERG), which involved averaging a high number of responses.

After adjustment for the number of years of education and alcohol use, there was a significant increase for cannabis users of the amount of time it took for the retina to transmit signals to the brain.

‘This finding provides evidence for a delay of approximately 10 milliseconds in the transmission of action potentials evoked by the RGCs,’ the authors wrote in JAMA Ophthalmology.

‘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.’