Are marijuana’s effects on vision good or bad? Two new studies suggest there isn’t one easy answer, and neither one considers long-term impacts.
One study of tadpoles suggests marijuana may enhance night vision, while a human study indicates that regular cannabis use may delay the processing of visual information in the retina.
The first study explains a cellular mechanism by which marijuana may improve night vision. The research is based on an observation that Jamaican fisherman who smoked or consumed marijuana had excellent night vision. In the new study, researchers at McGill University in Montreal applied a synthetic cannabinoid to the eye tissues of tadpoles. They found the cannabinoids made certain retinal cells more sensitive to light, and improved the speed and which the eye responded to even dim stimulus, The Guardian reports. Cannabinoids are the general class of chemicals that can interact with cannabinoid receptors in the brain. The body naturally produces some cannabinoids. Other cannabinoids come from marijuana or other sources.
The second study included 28 marijuana users and 24 people who did not use the drug. The researchers compared the working of the retina in both groups to see whether marijuana affects the function of cells called retinal ganglion cells. These cells are responsible for transmitting electrical pulses from the eye into the brain, CNN reports.
The study found there was a delayed response time for marijuana users compared with people who did not use the drug. This may impact the eyesight of people who use marijuana regularly, even if the influence is very weak, the researchers said.
“These studies both have interesting findings, but neither answers the question of whether marijuana affects vision over the long term,” says Raj Maturi, MD, associate professor of ophthalmology at Indiana University School of Medicine. “Marijuana might help some aspects of vision in the short term, but it might be harmful if used chronically. These findings suggest we need longer-term studies of the effects of chronic marijuana use on vision.”
Dr. Maturi notes that patients with glaucoma often say they have heard that marijuana may be helpful by lowering pressure in the eye. He tells them marijuana may be able to decrease the pressure a little bit, but at the same time the drug is acting on the brain and nervous system in ways that may be harmful.
“My view is that eyedrops that decrease the pressure in the eye are far more useful. You would have to smoke quite a lot of marijuana to get the same effect,” Dr. Maturi says.
Some studies on glaucoma and marijuana have found that when marijuana is smoked or when a form of its active ingredient is taken as a pill or by injection, it does lower pressure in the eye, or intraocular pressure. However, it only lowers the pressure for a short period of time—about three or four hours.
The American Academy of Ophthalmology does not recommend marijuana as a treatment for glaucoma.
A new report by the National Academy of Sciences on the health effects of marijuana concludes that studies suggesting positive effects of marijuana on glaucoma “have shown only short-term benefit on intraocular pressure (hours) suggesting a limited potential for cannabinoids in the treatment of glaucoma.”
Speak with your ophthalmologist to find the glaucoma treatment option that is best for you.