Glaucoma affects more than 60 million people worldwide and the second leading cause of blindness behind cataracts. Both marijuana and THC have been shown to lower intra-ocular pressure, which is a key contributor to glaucoma. One of the most well known uses for medical marijuana is
The most common form of glaucoma is called primary open angle glaucoma and represents a slowly progressive disorder that destroys cells in the retina and also degrades the optic nerve. A person’s visual field gets constricted and eventually disappears. The patient goes blind.
Three factors have been identified which create risk factors for glaucoma. The first two are out of a person’s control = Age and Race. The third, increased intra-ocular pressure, is the one that’s potentially controllable.
Intra-ocular pressure normally results from the eye shape being maintained by fluid in the eye called aqueous humor. The fluid flows between the front of the eye and the back of the cornea. If a person has increased intraocular pressure, the flow of fluid from the front of the eye is restricted, and the pressure rises. It is this fluid that is suspected to provide nutrients to the optic nerve.
Reducing intra-ocular pressure to normal does not guarantee glaucoma prevention, but since it’s the only controllable risk factor, it is the one that is worked on with medications.
The two ways that medications work on reducing intraocular pressure are as follows:
1) Reducing the production of aqueous fluid 2) Making it easier for the fluid to flow out of the front eye
There are also a few surgical options which attempt to achieve the same objective.
Several studies have shown the effects of marijuana and THC on reducing intraocular pressure. Whether the THC is smoked, inhaled, or eaten, intraocular pressure is reduced. Applying cannabinoids directly to the eye did not work however.
Research has not shown us exactly how cannabinoids reduce IOP. They work at reducing IOP for about 4 hours. That means having to take it 4 to 8 times per day, whereas, there are other medications only necessary twice per day.
The side effects of marijuana intake, such as the psychoactive effects, may be difficult for the elderly to tolerate. Marijuana may cause the heart to “race” and make patients anxious. The IOP in patients with glaucoma needs to be controlled continuously since it’s a progressive disease.
With the onset of the latest medications that are effective for controlling the IOP in glaucoma, marijuana is no longer a first line treatment for controlling it. It is less effective and potentially more problematic than the latest medications. If, however, a patient needs a second or third line choice, marijuana may fit the need nicely.