Glaucoma is one of the most serious — and common — eye conditions in the world. According to the Centers for Disease Control and Prevention (CDC), it’s the second-leading cause of blindness, affecting around 3 million American adults. Unlike other common conditions, like cataracts, its effects are irreversible, though they can be minimized and managed if detected before they progress.
Could cannabis be useful in this regard? It’s a question that has spurred a heated debate in recent years, with a number of prominent glaucoma patients speaking openly about their positive experiences with the plant. Actress Whoopi Goldberg even penned an op-ed for The Cannabist in which she said her “vape pen has changed my life” by helping relieve the intense headaches caused by her glaucoma. In many states with medical marijuana programs, glaucoma is among the conditions that qualify patients to apply for a cannabis prescription.
However, despite the anecdotal reports and the high-profile endorsements of cannabis’ usefulness for treating glaucoma symptoms, the medical establishment is decidedly opposed to it. The American Academy of Ophthalmology, the American Glaucoma Society, and the Canadian Ophthalmological Society have all been clear and unequivocal that the plant is not a viable treatment for glaucoma — to cite just one example, the first organization conducted a review that found “no scientific evidence demonstrating increased benefit and/or diminished risk of marijuana use in the treatment of glaucoma compared with the wide variety of pharmaceutical agents now available.”
To understand why cannabis is a less-than-ideal option for treating glaucoma, it’s important to have a little background on the condition itself. Essentially, glaucoma is a condition in which the eye is subjected to increasing amounts of pressure. This is known as interocular pressure, or IOP. This pressure can damage the optic nerve (which connects the eye to the brain) and restrict the eye’s field of vision. Left untreated, it can eventually cause the loss of peripheral vision and even total blindness.
Interocular pressure needs to be managed around the clock, which means the medicines used to do so need to be ingested around the clock as well. This is not a task for which cannabis is well-suited. As Dr. Craig J. Chaya, a glaucoma specialist at the John A. Moran Eye Center, told the University of Utah’s Health Feed Blog, patients “would need to smoke marijuana six to eight times a day … to get the benefit of a consistently lowered IOP. Smoking so much of it daily would leave you too impaired to drive, or operate equipment, or function at the peak of your abilities.”
His viewpoint has been corroborated by a number of scientific papers, including a 1998 study published in the Archives of Ophthalmology that found “[smoking] of marijuana plant material for the reduction of elevated IOP in glaucoma is ill-advised, given its toxicological profile.” However, that study also suggested that exploring the potential of cannabis-derived compounds “for use as topical or oral antiglaucoma medications seems to be worthy of further pursuit.”
Unfortunately, that line of inquiry doesn’t seem to have panned out either. Initially, some scientists believed the non-intoxicating cannabis compound CBD could be useful for treating glaucoma symptoms, as it doesn’t activate the brain receptor that causes the high traditionally associated with cannabis. However, a 2018 study from researchers at the University of Indiana showed that CBD actually increases interocular pressure, thereby worsening the symptoms of glaucoma.
On the other hand, the intoxicating compound THC has been shown to reduce IOP — but scientists haven’t been able to devise a delivery mechanism that lets patients take advantage of its benefits without leaving them in a constant stupor. According to a 2014 review of the available scientific literature published in Glaucoma Today, “it has not been possible to formulate sufficiently concentrated therapy due to the low water solubility of the active ingredients [THC].” The review also noted that most THC-infused eyedrops “have been toxic to the ocular surface and have not been tolerable due to local side effects.”
While it’s certainly possible that these issues could be solved in the future, for the time being, they seem to preclude the possibility of cannabis being a safe, useful treatment for glaucoma.