Marijuana can be used to treat glaucoma, which increases the pressure in the eyeball, injuring the optic nerve and causing loss of vision. According to National Eye Institute, marijuana lowers the pressure inside the eye. Marijuana, when smoked, lowered intraocular pressure (IOP) in people with normal pressure and those with glaucoma.
These effects of the drug can prevent blindness!
However, what actually causes blindness in glaucoma is damage to the optic nerve, which connects the eye to the brain. Each eye only has one, so it is important to protect it. Because marijuana lowers blood pressure as well as intraocular pressure, it can reduce the optic nerves blood supply. If you have glaucoma, that nerve has already suffered some damage. Lowering the blood supply may not be beneficial.
If you have glaucoma, it is important to lower your eye pressure 24 hours a day. Researchers estimate you would need to consume marijuana several times daily to achieve this. Cannabinoids have all been shown to reduce IOP significantly in both glaucoma patients and healthy adults with normal IOP, because of the role cannabinoid receptors play in ocular tissue.