It’s a telltale sign that you’re high: red, bloodshot eyes. Aka, weed eyes.
But as societal attitudes shift on cannabis legalization in Canada, so too has the conversation around the effects of cannabis on the eyes.
While you may not want to show up to a job interview or get pulled over by a cop looking bleary-eyed (more on that later), there’s new research to suggest herb might actually help eye health in the long run.
“Back in the day, we used to carry Visine to make red-eye go away,” says Abi Roach, founder of Toronto-based cannabis lounge Hot Box Café. “The amount of people that use Visine now as opposed to 15 years ago has completely changed. I don’t think people feel that fear of, ‘Oh my god! Somebody may think I’m stoned!’”
Today, “weed eyes” are widely regarded as an innocuous inconvenience. But more interesting for researchers is how cannabinoids can be used to treat diseases of the eye. Since cannabis was legalized in Canada last year, eye doctors have noticed an uptick in the number of patients interested in using marijuana as a treatment for glaucoma.
The primary method for treating glaucoma is to lower the intraocular pressure (IOP), or fluid pressure, in the eye. As far back as 1971, American researchers found that marijuana reduced IOP by 25 to 30 per cent for three-to-four hours in “11 youthful subjects.” Although there have been other studies on THC and glaucoma since the 70s, the drug’s status as a prohibitive substance prevented more research from being conducted.
Lisa Prokopich, a clinical professor of ocular health at the University of Waterloo, says research is so far inconclusive. “Yes, cannabis does lower eye pressure but only for a short time and not consistently, which we need for treatment of glaucoma.”
For most doctors, the side effects of THC outweigh the short-acting medical benefits for eye patients – given that marijuana also causes dry mouth, shallow breathing and cognitive impairment.
But Prokopich sees “much potential with cannabinoids if we can get them to the right place in the right concentration. But that’s a lot of ifs.”
THC drops are an option, but THC can cause irritation when applied to the eye. THC is also not water-soluble.
In fact, some research suggests that cannabis can enhance night vision. Prokopich says more research is needed to determine other effects of cannabis on the eyes, including effects on driving performance.
Legalization in Canada may have rid recreational users of the paranoia of getting busted by the cops if you’ve got weed eyes. But not if you’re driving. MADD Canada’s website, for example, lists red, watery and glassy eyes as a sign of pot intoxication.
Roadside tests administered by the police to test for marijuana use include an eye examination. If the driver fails, they must undergo a 12-step evaluation with a Drug Recognition Expert that also involves measuring pupil size under different light conditions.
Legal experts have criticized the testing as outdated. They say the test leaves room for police bias and notes that the tests have led to wrongful arrests.
Says Prokopich: “We do know driving is an issue with cannabis. Most people assume it is cognitive effects but there may be visual effects, problems with motion discrimination and contrast in low light levels.” But, she adds, “it’s not something you can measure on the side of the road.”
