What is Glaucoma?
Glaucoma is a condition of the eye that results in prolonged damage to the optic nerve. The overwhelming cause of this damage is intraocular hypertension, or pressure inside the eye caused by an increased presence of aqueous humor. This is the clear fluid that fills the space between the cornea and the iris. Glaucoma affects around 2 million people in the United States, and the majority are over the age of 45.
Glaucoma has very few symptoms, and often times the first symptom is the loss of peripheral vision. Vision loss due to glaucoma is currently irreversible. It’s caused when pressure in the eye damages the optic nerve. The exact mechanism of this is not clearly defined, concerning whether the pressure itself damages the eye tissue, or if it induces a chemical response that is toxic in nature. The latter is presumed by a majority of authoritative sources, however.
When the eye produces too much of this fluid, it accumulates inside the eye, putting pressure on the retina and optic nerve. The optic nerve is a bundle of millions of individual nerves connected to the retina. Pressure on the optic nerve impacts the fibers that are near the exterior first, so that’s why peripheral vision loss is usually the first symptom. The mechanism is outlined below.
The pressure that causes all of this damage occurs when the eye fails to drain this aqueous humor. There is a layer of spongy tissue called trabeculae located where the cornea, which is like the external lense of your eye, intersects with the iris, the colored part of the eye. In the angular crevice formed by these two tissues, the trabeculae filters the fluid into the bloodstream.
When the trabecular tissue becomes inflamed or damaged, it loses its ability to drain the fluid produced by the eye. This is called open-angle glaucoma, and 90% of cases of glaucoma fall into this category. No one knows what causes either type of glaucoma, but there are many medications that can either open the trabeculae, or decrease the production of aqueous humor. They have heavy side-effects, however, so many turn to more natural remedies.
How does CBD interact with glaucoma?
As with the vast majority of conditions and disorders which CBD has helped treat, glaucoma is caused at its root by an imbalance; in this case, an imbalance between the production and drainage of aqueous humor. Furthermore, multiple studies here and here have shown a strong positive correlation between the use of cannabinoids and attenuation of both the symptoms and the vaguely-understood causes of glaucoma.
At the optic nerve
To understand why pressure causes nerve death is fundamental in understanding how CBD can help. Increased pressure on the optic nerve causes the individual neurons to produce inordinate amounts of peroxynitrite, which is a potent oxidant. This induces apoptosis, or programmed cell death, within the individual neurons.
CBD is able to prevent this route of apoptosis in three ways:
- CBD is a potent antioxidant, and it immediately breaks down peroxynitrite (O-N-O-O+) on contact.
- CBD and other cannabinoids prevent the formation of O-N-O-O+ inside the cell, by inhibiting the enzyme that oxidizes it in the first place.
- It increases the threshold of all of the mechanisms of apoptosis, thereby making it more difficult for a stimuli to be seen as so devastating that cell death is necessary.
By preventing apoptosis of neurons, CBD prevents blindness. There are few drugs that work on so many different mechanisms as CBD and other cannabinoids including CBG, CBN, and CBV.
At the Trabeculae
The trabeculae is a porous membrane near iris that drains aqueous humor from inside the eye into the bloodstream. When this drainage system is backed up, pressure can build in the eye, and this leads to the condition of glaucoma. CBD and several other phytocannabinoids work through various mechanisms of action to attenuate this blockage, both by increasing drainage outflow and decreasing aqueous humor production.
CBD is capable of decreasing the causation of glaucoma through imbalance of intraocular pressure of aqueous humor through the following pathways:
- CBD and phytocannabinoids, through modulation of CB1 receptors, cause a decrease in the calcium ion and increase in the potassium concentrations in the endothelial cells of your eyes, which causes a decrease in the production of aqueous humor (AH) and therefore of pressure.
- CBD dilates the capillaries that filter and drain the AH from trabecular tissue. These blood vessels can narrow due to a number of stimuli, but cannabinoid modulation in that tissue widens both the vessels and the network of vesicles that transport fluid from the eye to the blood.