Can Cannabis Treat Glaucoma?

In July of 2015, Alice Donahue* reluctantly spent an afternoon at her doctor’s office. The 54-year old Fredericton mother of three had been experiencing blurred vision and headaches, but dismissed her symptoms as merely “finally needing glasses.” She would’ve skipped the visit altogether, but her husband insisted. “I wasn’t expecting glaucoma,” she says.

Glaucoma is a progressive eye disease often characterized by a painful increase in pressure within the eye. It can lead to vision loss, total blindness, and in severe cases, removal of the affected eye. Glaucoma ranks as the world’s second leading cause of irreversible blindness. It is estimated that more than 250,000 Canadians suffer from the disease.

Fortunately, blindness is no longer the inevitable outcome of a glaucoma diagnosis. With early detection and medical attention, significant vision loss can often be prevented. Some patients report success treating their glaucoma symptoms with cannabis, although the practice is not without controversy.

How cannabis works on glaucoma

One of the first studies assessing cannabis’s impact on glaucoma was conducted in 1971, by Drs. Hepler and Frank of UCLA. Their landmark paper noted that eye pressure could be reduced up to 30 per cent for up to four hours with a single dose of cannabis.

Retired California physician Dr. Lidja Kowalczyk finds Hepler and Frank’s results relevant today. “I’ve seen it firsthand,” she notes. “Patients suffer from severe eye pain and bad headaches. A little cannabis and they can get on with their lives.”

“Our eyes are part of the body’s endocannabinoid system, meaning our bodies have natural cannabis receptors in the eye tissue.” Dr. Kowalczyk explains. “When we ingest cannabinoids, they interact with those receptors and have the ability to reduce intraocular pressure. [And] cannabis’s inherent anti-inflammatory properties deliver additional relief.”

Relieving intraocular pressure with smoked or vaporized cannabis, however, is relatively inefficient, with most patients dosing every three to four hours to maintain ideal pressure. And while cannabis-infused edibles promise longer-lasting effects, variable absorption rates are a concern.

Potential dangers

Frequent, repetitive dosing with cannabis can bring unwanted psychotropic effects. Moreover, little research can attest to its long-term impact on glaucoma. For these reasons, as well as others, The Canadian Ophthalmological Society (COS) does not support the use of medical cannabis for glaucoma, citing a preference for other “more effective and less harmful” treatment options. The COS is particularly concerned for individuals who opt to smoke their medicine, since smoking in general is a known antagonist of eye health, and smoking cannabis specifically is also linked to various cancers.

Even for patients who eat or vaporize their medicine, blood pressure is a potential issue. Glaucoma-related blindness happens when the single nerve that connects the eye to the brain becomes damaged. Cannabis doesn’t only lower intraocular pressure, it also lowers overall blood pressure, with the potential to reduce blood flow to the already damaged optic nerve, and cause further deterioration.

The future of cannabis as a glaucoma treatment

New drug delivery methods, including topicals, such as cannabis-based eye drops, offer the potential for treatment without harmful or limiting side effects. To date, researchers have had little success in developing such a medicine, and the future of widespread cannabis-based glaucoma treatments is fuzzy.

But for Alice Donahue – who tried other methods, but prefers smoking – the benefits of medical marijuana outweigh the risks. “It has really helped me,” she says. “I don’t have headaches anymore, and I seem to be holding steady. Everything has some risk attached to it. For me, treating glaucoma with cannabis is the right choice.”

*Donahue is a pseudonym used at Alice’s request.