Glaucoma is a devastating eye disease that, if left untreated, can lead to blindness. More than 250,000 Canadians have chronic open-angle glaucoma, which is the most common form of the disease.
Certain people are at an elevated risk of developing glaucoma, particularly:
- The elderly
- Those of African descent
- Folks with a family history of glaucoma
However, the disease can strike anyone at any age, even children.
Medical marijuana has long been an option for people with glaucoma. And there’s plenty of anecdotal and scientific evidence suggesting cannabis helps relieve some of the intraocular pressure that comes with glaucoma.
While there’s no evidence to suggest that cannabis is able to reverse the effects of glaucoma, it’s used to slow the progression of the disease in some patients.
Let’s take a look at what glaucoma is and how cannabis should—and should not—be used to help ease its symptoms.
What Is Glaucoma?
Glaucoma is an eye condition that causes damage to the optical nerve through increased eye pressure. In open-angle glaucoma, which accounts for 90% of glaucoma cases, the trabecular meshwork of the eye becomes blocked.
The trabecular meshwork is responsible for draining a fluid called aqueous humour from the eye. With the meshwork blocked, this fluid builds up and creates ocular pressure.
Over time, the pressure damages the optic nerve, and this leads to vision loss. Because glaucoma can occur very slowly—often over many years—people may not realize their vision is deteriorating until the disease has reached an advanced stage. At this point, vision loss may be permanent. While glaucoma is a fairly common disease, science still hasn’t uncovered why it happens.
In rarer cases, glaucoma can occur even when the trabecular meshwork isn’t blocked. In angle-closure glaucoma and pigmentary glaucoma, for example, eye fluid becomes blocked for other reasons. In normal-tension glaucoma, there’s no pressure in the eye, yet the individual still suffers from optic nerve damage typical of glaucoma for reasons that scientists haven’t yet been able to explain.
The Science Behind Cannabis’s Effect on Glaucoma
Many glaucoma sufferers have long used medical marijuana to help them manage the symptoms of their disease. Scientific studies have found that tetrahydracannabinol (THC) reduces eye pressure, which in turn helps slow glaucoma’s progression.
In one of the earliest scientific studies showing the medical benefits of marijuana, researchers in 1971 found that cannabis can lower pressure in the eye by up to 30%. While it’s clear that THC reduces pressure in the eye, scientists have yet to uncover the specific mechanism for why this is the case.
Another recent study found that while THC lowers eye pressure, cannabidiol (CBD) doesn’t have the same benefit. Researchers at Indiana University actually discovered that CBD increases pressure in the eye, which can cancel out the therapeutic benefits of THC for glaucoma sufferers.
The results of the study may come as a surprise given that CBD is often associated with numerous health benefits. While CBD certainly does have many proven health advantages, the results of the study suggest that folks with glaucoma are better off avoiding CBD-predominant products and sticking with ones that are rich in THC.
Also, glaucoma patients need to be careful about smoking marijuana. Smoking the plant can reduce blood flow to the optic nerve and cause pressure in the eye to become unstable, potentially making the glaucoma worse.
For this reason, many doctors only recommend cannabis as an option for advanced glaucoma and not for early- to mid-stage glaucoma. If you have early- to mid-stage glaucoma, talk to your doctor about more appropriate options, such as eye drops and laser surgery.
How Glaucoma Sufferers Can Take Marijuana
If, in consultation with your doctor, you’ve decided that cannabis may be appropriate for you, make sure you’re doing so properly. There have been companies trying to develop cannabis eye drops for glaucoma sufferers, but no one has yet hit on a formula that’s actually effective.
Inhaling cannabis may provide relief, but it will only last for a few hours, until the THC’s effects wear off. Plus, as mentioned, smoking cannabis may worsen glaucoma by destabilizing pressure in the eye. For these reasons, glaucoma sufferers may want to ingest cannabis orally in the form of a tincture or an edible.
When choosing a cannabis product for treating your glaucoma, you should opt for something with a high-THC content and little to no CBD. As stated above, CBD may actually increase pressure in the eye, which is the last thing you want if you suffer from glaucoma. Again, make sure you consult with your doctor before choosing any cannabis products.
Clearly, many glaucoma sufferers have had success taking cannabis. When used properly, cannabis can slow down the progression of glaucoma and even help folks retain their vision.
However, the science behind marijuana and glaucoma is complicated. Ongoing research will hopefully provide us with a clearer picture of how marijuana can be best used to help alleviate this devastating disease.
Photo credit: Eric Ward