What is glaucoma?

Glaucoma is a combination of eye illnesses that damage the optic nerve (which connects the eye to the brain) at the back of the eye, resulting in vision loss and blindness. It is caused by increased internal ocular pressure (IOP), which is when fluid starts collecting in the front of the eye, increasing pressure inside the eye.

It can affect people of different ages; however, glaucoma is most commonly seen in those between 70 and 80. Early treatment is important because there is no cure. The symptoms might appear gradually, making them difficult to detect. A full dilated eye exam is the only method to determine whether or not you have glaucoma.^1,2

Interest in cannabis (marijauna)

Cannabis consists of dried flowering leaves and buds from the Cannabis sativa plant and is often called marijuana or weed. And it is a plant with many powerful uses. It is reported to help reduce IOP. Delta-9 tetrahydrocannabinol (THC) was found and isolated as the primary active component in 1964. The plant includes around 400 chemicals, the majority of which are related substances known as cannabinoids. Marijuana and THC have been demonstrated to reduce IOP in 60-65% of both healthy people and glaucoma sufferers. The average IOP drop in one research study was around 25%.³

The strength of THC and other cannabinoids varies significantly depending on the plant material utilised. Cannabis plants and their derivatives, THC and Cannabidiol (CBD), have been studied for the treatment of a variety of conditions, including decreasing intraocular pressure. Controlling IOP is the most important controllable risk factor for glaucoma, an optic neuropathy that causes permanent vision loss.⁴

Understanding intraocular pressure (IOP)

What is IOP?

The rear of the eye contains the vitreous humour. The vitreous humour, or vitreous fluid, is a clear, colourless, gel-like material that occupies the area between the lens and the retina in the eye, whereas the front section, located between the cornea and the iris, is filled with aqueous humour. 

Aqueous humour is less thick and more watery compared to vitreous humour. Intraocular pressure refers to the force or pressure within your eyes. In particular, it’s an assessment of the fluid pressure within your aqueous humour. Your eyes have a specific pressure to function well. Untreated elevated eye pressure may result in glaucoma and damage to your eyesight.⁵

Measuring eye pressure

Eye pressure is assessed in millimetres of mercury (mmHg). Typical eye pressure varies from 10 to 21 mm Hg, with pressures exceeding 21 mm Hg regarded as elevated. High pressure in the eye can result in nerve damage and faster vision loss. Ocular hypertension occurs when the IOP is above the normal range, yet the individual exhibits no symptoms of glaucoma.⁶

Cannabis and its active compounds

Cannabis is a type of plant primarily recognised for generating a group of substances referred to as 'cannabinoids'. More than 60 distinct cannabinoids exist in nature, yet only a few have been thoroughly studied. THC is the primary psychoactive component. Other well-known cannabinoids include Cannabidiol (CBD) and Cannabinol (CBN). The Cannabinoid composition changes based on the cannabis plant species, the cultivation method, and the specific part of the plant that is collected.

 Surprisingly, the participants exhibited a variation in intraocular pressure between +4% and - 45%. Later research has shown that around 65% of eyes affected by glaucoma will see a 30% decrease in pressure following Cannabis inhalation. The effect of reducing pressure persists for three to four hours and depends on the dosage.⁷

Why isn't cannabis an effective treatment for glaucoma?

From 2006 to the present, numerous studies have examined the impacts of THC and CBD on eye pressure. At low doses, CBD reliably demonstrated no impact on the eyes. THC, when smoked, inhaled, or consumed, can reduce intraocular pressure (IOP) by up to 40% when administered at elevated doses (40 mcg). This is nearly as effective as prescription anti-glaucoma medications, but it also causes patients to get intoxicated. Regrettably, any effect of lowering IOP diminished rather swiftly. In the meantime, THC drops for glaucoma proved ineffective and frequently resulted in an itchy or burning feeling in the eyes.

So does cannabis lower IOP?

The brief response is yes. But is it possible to turn this into a lasting solution? In this situation, we must consider things realistically.

The primary obstacle is the brief duration of THC's effects. Primary open-angle glaucoma is a long-lasting condition that results in gradual harm. To prevent it from deteriorating, you should consume THC at consistent intervals – typically every hour or two.

This would necessitate that you remain continually influenced by THC. Daily activities like driving, making choices, or concentrating at work would be unfeasible. Though these might appear enjoyable for leisure, if encountered continuously, they turn into significantly disruptive side effects.

In the meantime, there isn't a secure CBD dosage for glaucoma. While it holds promise for various conditions, it could ultimately cause more harm than benefit over time. Consequently, the National Eye Institute (NEI), the American Glaucoma Society, and the American Academy of Ophthalmology (AAO) do not endorse marijuana as a glaucoma treatment.⁸

How to lower the risk of the cannabis effect?

In patients with glaucoma, the drug might cause tachycardia (heartbeat fluctuations) and reduce blood pressure, potentially diminishing blood circulation to an already affected optic nerve.⁹

Cannabis use comes with certain risks. The best way to protect your health is to entirely avoid cannabis and cannabis-related products. Cannabis can be ingested through various methods. The most prevalent are inhalation (smoking) and ingestion (food or beverages).

Each response is different with respect to:

• Sex
• Age
• THC and CBD content
• Any pre-existing medical conditions
• Experience with cannabis, frequency of use
• Taking  alcohol, other drugs or health products

To minimize the risks associated with cannabis use, it is advised to use it in a secure setting with reliable people, postpone use until brain development is complete, select products with greater CBD levels, refrain from deep inhalation, limit and decrease consumption, avoid combining cannabis with alcohol or drugs, steer clear of using cannabis while driving or operating machinery, and refrain from using synthetic cannabis products. 

If you are susceptible to mental health issues like psychosis, schizophrenia, or substance use disorders, it’s advisable to steer clear of cannabis entirely. These actions can aid in avoiding severe health problems and lowering the likelihood of addiction and mental health concerns.¹⁰

Temporal validity of studies

When the initial studies on marijuana's impact on IOP appeared in the 1970s, there were a limited number of glaucoma medications available, and they produced concerning side effects. Those medications have since been improved and replaced by more effective drugs that have fewer side effects.

Glaucoma is now mostly treated with eye drops that decrease the IOP. Even though we can't fully fix glaucoma, the eye drops used today are safer and work better than marijuana. They also last up to 12 or 24 hours, so you only need to use them once or twice a day. Alternatively, laser surgery is another way to treat glaucoma.

Research was conducted into THC-based eye drops, a main part of marijuana. They found out these drops don't help lower IOP as they don't soak into the eye well and cause a lot of pain and red eyes. Individuals considering marijuana for use should be aware that although the substance can temporarily reduce IOP, its use comes with numerous limitations, such as its brief duration of effects, potential side effects, and health risks, especially when inhaled.¹¹

Summary

Glaucoma is an eye disease that causes vision loss and potentially blindness due to increased intraocular pressure (IOP). It is most common in individuals aged 70 to 80 and requires early detection. Cannabis, known for its cannabinoids like THC and CBD, has shown promise in managing IOP, with studies showing it can reduce IOP by 25%. 

Yet, the use of Cannabis to treat glaucoma is still up for debate due to its mind-altering effects and the fact that a safe CBD amount isn't known. Organisations like the National Eye Institute and the American Glaucoma Society do not back cannabis as a fix, pointing out the need for steady and sure ways to manage it. To cut down on risk, it's best to refrain from Cannabis use. Nowadays, drops and laser surgery are seen as better choices for treating glaucoma properly and safely.