Seeing the possibilities: Glaucoma and medical cannabis treatments

What is Glaucoma?

Glaucoma is a common eye condition that causes a build-up of pressure in the eye. In most cases of glaucoma (open angle glaucoma), this pressure is due to drainage channels in the eye becoming blocked over a long period. This pressure causes damage to the optic nerve, which sends signals from the eyes to the brain. Over time, this can lead to significant vision loss and eventually blindness.

Other, less common, types of glaucoma include:

• Acute angle closure glaucoma occurs when drainage in the eyes becomes suddenly blocked, quickly raising the pressure inside the eye.
• Secondary glaucoma: caused by an underlying condition such as uveitis or diabetes.
• Childhood (congenital) glaucoma: occurs in infants and young children due to abnormalities in the eye.

The exact cause of glaucoma is often unknown; however, the risk of developing glaucoma can be linked to genetics, an underlying condition such as diabetes, or age (glaucoma can affect people of all ages but the risk of developing the condition increases as you get older). 

What are the symptoms of glaucoma?

Glaucoma tends to develop slowly, often over many years, and there are usually no symptoms associated with the condition at first. Eventually, patients with glaucoma may notice issues with their peripheral vision, later extending to blurriness or glare around light sources. 

Other later symptoms can include:

• Headaches
• Eye pain
• Red and tender eyes
• Nausea and vomiting

The lack of early symptoms often means patients are unaware of their condition. However, it can be detected through routine eye tests before it causes any noticeable symptoms. You should book a routine eye test at least every two years - even if you don’t need glasses.

Treatment for glaucoma

There is no cure for glaucoma and vision loss as a result of the condition cannot be restored; however, it is possible to prevent further damage. Glaucoma treatment can include several approaches, including medications to lower eye pressure, and surgery to improve drainage from the eye. However, other treatment options may also be helpful for managing glaucoma. 

Medical cannabis and glaucoma

Cannabis has been used as a treatment for a wide range of conditions for thousands of years. Some historic texts even refer to the use of the plant in treatments for the eyes. While it is unclear whether this refers specifically to glaucoma, more modern evidence has demonstrated some potential benefit of cannabinoids in this setting. 

Research into the potential of medical cannabis for glaucoma has been ongoing since the early 1970s. The basis for this potential lies in the presence of cannabinoid receptors (CB1 and CB2) in various parts of the human eye. Several studies have been conducted to determine whether interactions between cannabinoids from the cannabis plant could be useful in lowering intraocular pressure - the primary cause of glaucoma.

What does the evidence say?

Some research indicates that the endocannabinoids 2-AG and AEA are present at high levels in the healthy human retina; however, in eyes with glaucoma, the levels of these compounds may be low. This suggests a role for the endocannabinoid system in regulating intraocular pressure. Moreover, some researchers suggest that the neuroprotective effects of cannabinoids may be useful in treating a neurodegenerative condition, like glaucoma.

In 1971, researchers found that eating or smoking cannabis was associated with a 5-45% reduction in intraocular pressure; however, the effects lasted only a matter of hours. In 2002, a study of nine patients with glaucoma found that THC was effective at temporarily reducing intraocular pressure, but high and frequent doses were required resulting in most patients discontinuing the treatment due to potential toxicity.

Later studies have demonstrated similar effects. However, the potential need for frequent dosing and subsequent adverse effects of cannabinoids have largely prevented their use in a clinical setting for the treatment of glaucoma. Nonetheless, their ability to lower intraocular pressure, combined with their neuroprotective effects warrant further research into the use of medical cannabis for glaucoma.

Can I get a medical cannabis prescription for glaucoma?

Glaucoma is a common and debilitating eye condition that can have a significant impact on quality of life. While current conventional treatments can be effective in preventing further vision loss, they are not always suitable for everyone, and at times, cause unpleasant side effects. 

So, can cannabis stop glaucoma? Well, while some evidence suggests cannabis-based medicines may help reduce intraocular pressure and slow the progression of the disease, the research into its effects on common glaucoma symptoms, like vomiting, nausea, and headaches, is stronger. And so, in the UK, medical cannabis may be considered as an adjunctive or alternative treatment for patients with glaucoma if they are struggling to manage these symptoms.

If you’d like to learn more about medical cannabis and the conditions for which it can be prescribed, speak with one of our doctors today.