By William “Stash” Jones
Oregon Cannabis Connection
It seems most of the evidence about the effect of marijuana use on eyesight and the human eye have been generally positive, until a recent study was published in JAMA Ophthalmology.
Doctors have known for years that cannabis helps glaucoma symptoms. The tetrahydrocannabinol, or THC, found in cannabis helps decrease intraocular pressure and offer temporary relief for a few hours whether taken orally, sublingually, or ocularly. THC is the main psychoactive component in cannabis.
More recently in a positive study published in the Journal of Ethnopharmacology volunteers showed “consistent improvements” in night vision during testing. They performed hospital based tests and analogous field tests in Morocco with portable instrumentation. In the hospital they used Marinol, or synthetic THC, and in the field they used Kief, or natural powdered cannabis locally curated in Morocco. The report said, “In both test situations, improvements in night vision measures were noted after THC or cannabis.”
But in the December 2016 issue of JAMA Ophthalmology research seems to show a delay in the processing of visual information for cannabis users. The impact was very minimal, but measurable.
“Such an anomaly could be imperceptible for cannabis users,” explained Dr. Vincent Laprevote, lead author of the study and a physician at Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy in Laxou, France. “However, it is important, since it could reflect the changes in the communication between neural cells implied by regular cannabis use.”
The cells that the researchers focused on in the study are called retinal ganglion cells. They are located near the surface of the eye’s retina. These cells collect and transmit visual information to the brain. The study showed a slowing on the transmission of information in 54 relatively heavy cannabis users compared with 24 who did not use it.
Admittedly their study has a few limitations, and they mention those in their discussion:
“First, it is a pilot study involving a small number of participants. Consequently, PERG measurements would need to be replicated in a larger population; Second, because cannabis is widely used in conjunction with tobacco, particularly mixed together in joints, it is difficult to distinguish the effect of each compound; Third, although we found a delay in the response of the RGCs, we do not know if this delay is also detected at previous retinal stages. Full-field electroretinography measurements might be useful for addressing this issue; Finally, in future studies involving PERG measurements, it would be important to have visual acuity of at least 20/20 in each eye.”
More studies are needed to determine if these effects were truly caused by the cannabis, or other factors. Even though the effect is imperceptible, the overall physical impact is not well understood. Since there are definitive effects on the eye from cannabis that are well documented, it’s not a stretch to think this could be significant.
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