Ever since a 1971 study reported that smoking marijuana reduces eye pressure, the use of cannabis for glaucoma has remained a popular topic.
Indeed, it’s now commonly accepted knowledge that taking cannabis reduces eye pressure for several hours. More importantly, recent research highlights that the body’s endocannabinoid system is involved in eye health, and consequently, targeting it through cannabinoids and other compounds may be beneficial in glaucoma.
The Endocannabinoid System
First discovered in the 1990s, the endocannabinoid system is a network of receptors, endocannabinoids, and the enzymes that control the synthesis and breakdown of these compounds.
This system plays a critical role in human health through helping our bodies, maintaining homeostasis: a healthy state of balance. Research shows that the endocannabinoid system is involved in many key processes, such as cognitive function, immunity, pain, sleep, and even eye health.
So far, researchers have identified two main cannabinoid receptors: CB1 and CB2. Whereas CB1 is abundant in the central nervous system, CB2 is common in immune cells. These receptors respond to anandamide and 2AG-the two endocannabinoids made inside our bodies. In addition, they also interact with phytocannabinoids: cannabinoids that come from cannabis, such as THC and CBD.
THE Endocannabinoid system and Glaucoma
All parts of the endocannabinoid system, including receptors, endocannabinoids, and enzymes, are present in ocular tissue, suggesting that they play a role in healthy eye function.
More importantly, there’s evidence that glaucoma affects endocannabinoid system function. For example, one study compared the levels of 2-AG, anandamide, and PEA, a compound closely related to anandamide, in normal and glaucomatous eyes.
Although AEA levels were similar, diseased eyes had lower levels of 2-AG and PEA in a part of the eye called the ciliary body, which plays an important role in controlling eye pressure. PEA was also lower in the choroid, one of the outer layers of the eye.
Meanwhile, a study in rats with ocular hypertension, a condition that causes eye damage similar to acute glaucoma in humans, had even more interesting findings. In this experiment, hypertension led to increased levels of FAAH, an enzyme that breaks down anandamide, as well as a decrease in CB1 receptors.
More importantly, when the researchers gave the rats a compound that blocks FAAH or one that resembles anandamide, the retinal damage was reduced. This suggests that glaucoma may reduce anandamide levels in the retina and that this reduction contributes to retinal cell damage.
Findings such as these have led researchers to propose that “it may be possible to improve glaucomatous outcomes through therapeutic modification of the endocannabinoid system.”
Research shows that the endocannabinoid system can be harnessed to help with glaucoma in two ways: reducing intraocular pressure and providing neuroprotection.
For example, a 1996 study showed that applying topical, anandamide-like compounds to the eyes of rabbits resulted in a significant reduction of intraocular pressure, confirming that the endocannabinoid system regulates this process. Similarly, numerous studies have shown that cannabis and THC produce the same effect.
In addition, recent studies report that the endocannabinoid system can help with glaucoma by protecting neuron cells from damage, an effect known as neuroprotection.
The main way that glaucoma leads to blindness is by causing the death of a specific type of neurons found in the eye: retinal ganglion cells (RGCs). These cells can continue to be lost even when people are taking eye pressure-lowering drugs.
As it turns out, the endocannabinoid system can protect these neurons from damage that occurs during glaucoma. For example, one study found that raising levels of anandamide by blocking the FAAH enzyme protected rat RGCs from this damage.
Taken together, current research shows that influencing the endocannabinoid system by increasing endocannabinoids or using phytocannabinoids can be beneficial to glaucoma sufferers. As such, medical cannabis preparations may be helpful.
Cannabis & Glaucoma
The first piece of evidence that medical marijuana can help glaucoma sufferers came in 1971 when researchers discovered that smoking cannabis resulted in a significant reduction of intraocular pressure.
As for the neuroprotective effects of cannabis, current research is limited to animal and cell culture studies. For example, one study examined whether THC or CBD can prevent neuron damage caused by glutamate, a compound that contributes to neuron death in glaucoma. The researchers found that both cannabinoids protected the neurons.
Although such findings are not as clear cut as the effects of cannabis on eye pressure, there is enough evidence that both endo and phytocannabinoids can provide neuroprotection to retinal cells damaged by glaucoma.
However, it’s important to note that all evidence points to THC as the main cannabinoid responsible for the pressure-lowering effects of cannabis. CBD, on the other hand, may actually increase eye pressure.
For example, a 2006 study found that while sublingual (under the tongue) administration of THC reduced intraocular pressure, CBD either had no effect or actually increased pressure at higher doses. Similarly, a recent study in mice found that topical application of CBD increased intraocular pressure.
However, this doesn’t mean CBD should be disregarded entirely since it still has neuroprotective effects. If anything, this gives more support to the practice of using whole-plant cannabis preparations that combine significant amounts of THC and CBD and all other active compounds found in the whole plant.
All in all, current research evidence suggests that medical marijuana can be beneficial to glaucoma sufferers not only through reducing eye pressure but also protecting neuron cells. However, its medical use has been limited by side effects.
Although medical researchers remain optimistic about the potential of cannabis to help with glaucoma, eye doctors as a whole do not support its use due to adverse effects.
Most notably, cannabis is known to potentially cause psychoactive effects such as anxiety, paranoia, poor memory, and euphoria, collectively known as the cannabis “high.” Besides, cannabis has other adverse effects, including increased heart rate, palpitations, and reduced blood pressure. Crucially, lower blood pressure can decrease blood flow to the optic nerve, negating the benefits provided by reducing eye pressure.
These side effects are problematic because the pressure-lowering benefits of cannabis only last about 3–4 hours. Since eye pressure in glaucoma must be controlled at all times, this means people using cannabis would have to continuously suffer from these issues.
The significance of these side effects was highlighted by a study where nine people with glaucoma took THC capsules or smoked cannabis. All nine participants chose to discontinue the treatment after 1–9 months.
Due to the side effects described above, the American Academy of Ophthalmology — the largest association of eye doctors in the world — does not recommend the use of cannabis for glaucoma. This stance is matched by organizations in other countries, such as the Canadian Ophthalmological Society.
Having said that, the vast majority of countries with medical cannabis programs, including Canada, Germany, and the Netherlands, allow doctors to prescribe cannabis for glaucoma. There are only a few exceptions to this, such as the UK, where medical cannabis is only available for a select few conditions.
Meanwhile, in the United States the use of medical cannabis for glaucoma is permitted in the District of Columbia and 30: Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Hawaii, Illinois, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, North Dakota, Ohio, Oregon, Pennsylvania, Rhode Island, Washington, West Virginia, and Vermont.
Current research evidence highlights that influencing the endocannabinoid system is a promising way to treat glaucoma. Studies show that we can use this system to not only reduce eye pressure but also provide neuroprotection.
This latter finding is especially significant because some people with glaucoma continue to experience vision loss even after their eye pressure is reduced. As such, there’s a need for glaucoma medicines that address both eye pressure and neuronal damage.
Although cannabis is one potential candidate for such medicine, its use is currently limited by its short duration of action and significant side effects. For this reason, eye physicians do not recommend cannabis for glaucoma.
However, that doesn’t rule cannabis out completely. Researchers are currently testing a wide variety of compounds that affect the endocannabinoid system, including phytocannabinoids, synthetic cannabinoids, and compounds that increase endocannabinoid activity.
It’s quite possible that a cannabinoid-based medicine with longer duration and fewer side effects may be developed in the future.
Glaucoma is a condition in which the optic nerve is damaged, usually caused by a fluid build up inside the front part of the eye. As the amount of fluid increases, it pushes on the optic nerve and damages it. Prolonged damage to the optic nerve is an irreversible process that can lead to blindness in that eye. Glaucoma can happen to anyone, at any age, but it is most common among older adults. Glaucoma is the primary cause of blindness for people over aged 60. Even with treatment, 15% of people with glaucoma go blind in at least one eye within 20 years.
There are 2 main types of glaucoma:
Open-angle glaucoma is the most common type of glaucoma. If you have open-angle glaucoma, it means that there’s a problem with drainage of fluid in the corner of your eye—the trabecular meshwork—that lets fluid out, so that the pressure behind your eye remains constant. Like a clogged drain in a sink, fluid can’t leave your eye. Open-angle glaucoma begins gradually and slowly gets worse.
Angle-closure glaucoma, or closed-angle glaucoma, happens when your iris is too close to the drainage space, or drainage angle, that’s between the iris and the cornea. The iris can end up blocking the drainage space entirely, like a plate blocking the drain in the sink.
Angle-closure glaucoma can come on slowly, due to the iris gradually bulging forwards until it blocks the drainage angle. This is known as chronic angle-closure glaucoma. Like open-angle glaucoma there are no symptoms at first.
If you develop acute angle-closure glaucoma, it means that the drainage angle is completely blocked. If this happens, the pressure inside the eye can rise extremely fast. This is a medical emergency, leading to blindness within hours to days without treatment.
There are also other types of glaucoma that occur much less often. These include:
- Normal-tension glaucoma, when your optic nerve gets damaged even though your eye pressure stayed the same.
- Glaucoma in children can develop in early childhood, or be present from birth. In pediatric glaucoma, the optic nerve could be damaged by an underlying medical condition, or by a blockage to the drainage angle.
- Pigmentary glaucoma is when pigment granules from your iris settle in the drainage channel, blocking fluid from leaving your eye.
Open-angle and angle-closure glaucoma cause almost no symptoms when they first begin, making it very difficult to detect them early. That’s why it’s so important to get regular vision tests so that your eye doctor can spot and treat glaucoma as soon as possible. If you’re over 40 and have a family history of glaucoma, you should get an eye exam every 1-2 years. If you have health issues like diabetes, you might need one more often than that.
Glaucoma begins with a loss of vision in your peripheral vision. The first symptoms you might notice are patches of blindness either in your peripheral vision, or floating across your central vision. Glaucoma usually affects both eyes at once, but it is possible to get it in just one eye. As glaucoma progresses, you’ll start to experience tunnel vision, which will gradually close in until your vision is completely gone.
Acute angle-closure glaucoma has distinct symptoms. It’s important not to ignore them, but to go to your eye doctor or an ER immediately if you experience these symptoms:
- Blurred vision
- Seeing halos, or rainbow-colored rings, around lights
- Severe eye pain
- Nausea and/or vomiting
- Headache with change in vision that doesn’t dissipate
Glaucoma is generally caused by the build-up of fluid inside the eye due to a blocked drainage angle, but it’s not clear what causes this blockage occurs. Sometimes, its caused by a traumatic eye injury, or chemicals splashing into the eye. It can also be caused by an inflammatory condition that inflames and blocks the drainage angle. Rarely, it can also be a side effect to medications.
Usually, glaucoma develops without any clear cause, but researchers have identified certain factors that increase your risk of developing glaucoma:
- Being over 60 years old
- If you’re Black, Hispanic, or Asian
- A family history of glaucoma
- Extreme near-sightedness or far-sightedness
- An eye injury, or some types of eye surgery
- High internal eye pressure, also called intraocular pressure
- Corneas that are thin in the center
- If you have high blood pressure, diabetes, sickle cell anemia, or certain other medical conditions
- Taking corticosteroid eye drops, or other corticosteroid medication, for a long time
Your eye doctor will carry out a thorough eye exam that includes a few different tests that help diagnose glaucoma:
- Visual acuity test, using an eye chart to measure your vision at different distances.
- Visual field test to check your peripheral vision, since peripheral vision loss is a key symptom of glaucoma.
- Dilated eye exam, using special drops to widen your pupils, allowing your eye doctor to examine your retina and optic nerve in order to check for damage.
- Tonometry uses a special instrument, called a tonometer to measure the pressure inside each eye.
- Pachymetry uses an ultrasonic wave instrument to measure how thick your cornea is.
- Gonioscopy involves Inspecting the drainage angle of your eye.
Your eye doctor will also review your eye health history along with any other relevant medical history.
Once glaucoma damages your optic nerve, that can’t be reversed. Whatever vision loss you have from glaucoma can’t be cured. But it is possible to treat glaucoma to prevent it from getting worse and damaging your optic nerve any further, which is why it’s early detection is so important.
Treatments for glaucoma all focus on lowering the pressure inside the eye, so that the optic nerve isn’t damaged any further. Depending on your situation, you might be prescribed with eye drops or oral medications, or referred for laser treatment or surgery.
Eye drops for glaucoma include:
- Prostaglandins, like latanoprost (Xalatan) and latanoprostene bunod (Vyzulta). These medications reduce the amount of liquid flowing into your eye to bring down eye pressure. They have minor side effects and are used only once a day.
- Beta blockers like timolol (Betimol, Istalol, Timoptic) and betaxolol (Betoptic) help your eyes produce less fluid. They’re used once or twice a day, and can have side effects that include breathing difficulties, lowered heart rate and blood pressure, increased tiredness, and impotence.
- Alpha-adrenergic agonists like apraclonidine (Iopidine) and brimonidine (Alphagan P, Qoliana) both reduce the amount of fluid your eye produces, and encourage more fluid to drain out your eyes. These are usually taken twice a day, and sometimes three times a day.
- Carbonic anhydrase inhibitors like dorzolamide (Trusopt) and brinzolamide (Azopt) also reduce the amount of fluid produced in your eye. They have minor side effects, and are taken twice or three times daily.
Most eye drops don’t cause serious side effects, although they can make your eyes sting or itch, or bring on a headache. Because there are several types of eyedrops for glaucoma, you can ask your doctor to switch your prescription if the side effects are bothering you too much.
If you’re prescribed eyedrops for your glaucoma, it’s vital that you use them regularly. Because there are no symptoms for glaucoma until after your optic nerve has been damaged, it’s easy for people to forget to take their medications or to think that they don’t need them any more. Nothing could be further from the truth. If you feel like you don’t need your medications any more, that’s because they are working, and you need to keep using them so that they keep on working.
If eye drops don’t work to control your glaucoma, you might be prescribed with oral medications, generally a carbonic anhydrase inhibitor to bring down your eye pressure.
If your glaucoma doesn’t respond to eye drops or oral medication, you might need some kind of procedure to reduce the pressure in your eye. The most common treatment is laser therapy or laser trabeculoplasty.
Laser trabeculoplasty involves using a small laser beam to open up your blocked drainage space. It’s done in your doctor’s office or in an eye clinic, using local anesthetic to numb the eye.
The laser machine burns holes in your blacked drainage space to let the fluid flow out. Usually, the doctor will do one eye at a time. You’ll see flashing green or red light during the procedure, and you might feel soreness in your eye afterward. If both eyes need laser therapy, they’ll be treated a few days or a few weeks apart.
While laser therapy can be very effective, it doesn’t last forever. You might need to do it again eventually.
Your eye doctor might carry out filtering surgery, also called a trabeculectomy. It’s a procedure where the doctor opens up a new drainage hole to let the fluid out of your eyes. Sometimes, the doctor will put in a tiny tube to keep the drainage space open and stop it from getting blocked. You’ll be given medicine to help your eye muscles relax, and a local anesthetic to numb your eye, before the procedure, but generally, anesthesia is not commonly administered to you would be conscious for the exam.
You might also be advised to get minimally invasive glaucoma surgery (MIGS). These are procedures that help relieve eye pressure, but at less risk and requiring less postoperative care than a trabeculectomy or inserting a drainage tube. There are a few options available, so you need to discuss them with your doctor to decide on the best choice for you.
If you have acute angle-closure glaucoma, you’ll need to get surgery or laser therapy urgently, in order to relieve the pressure that builds up rapidly. Usually, you’ll also need to keep taking medication after the procedure.
Some people with glaucoma find that lifestyle changes and alternative therapies can also help treat glaucoma. Advice includes:
- Exercising carefully, since regular exercise can help reduce eye pressure.
- Drinking less caffeine.
- Sipping small amounts of fluids throughout the day, instead of drinking a large amount in one go, which can temporarily increase eye pressure.
- Trying herbal remedies, like bilberry extract, which may lower eye pressure.
- Using relaxation techniques to reduce stress, since stress can trigger acute angle-closure glaucoma.