Glaucoma is a major blinding disease, the second leading cause of loss of sight in the USA. The chief mechanism is excessive pressure inside the eyeball. Treatments focus on reducing this pressure, often through trying to reduce production of the intraocular liquid, aqueous humor, or to increase its drainage
Imagine inflating a basketball to twice its recommended pressure. Not only would it bounce and handle poorly, it would also be in some danger of exploding. In the eye, excess pressure can deform the back of the eyeball where the optic nerve leads deep into the brain. The pressure can cause “cupping,” and with it, irreversible optic nerve damage. The crushing effect causes excitotoxicity in the damaged retinal ganglion cells, and further injury results from this oxidation stress.
The function of cannabinoids in lowering this damaging interocular pressure is well known; the treatment of glaucoma with cannabis is one of the most readily identified medical uses of marijuana.
Now it is clear that the benefits go far beyond this crucial lowering of intraocular pressure. Activation of the endocannabinoid receptor system also now appears to provide robust neuroprotective effects. Not only does cannabis lower eye pressures, it also serves to help protect the visual nerve cells from damage.
Our eyes are well endowed with endocannabinoid receptors of both types, CB1 and CB2. CB1 receptors have been shown to flourish in the human anterior eye, where the excess pressure is generated, and the retina, where the damage of glaucoma takes place.
Research, reported in Investigative Ophthalmology and Visual Science, found CB1 receptors in all the frontal eye anatomy thought important in controlling IOP (intraocular pressure). These include Schlemm’s canal and “ciliary epithelium, trabecular meshwork, and in the blood vessels of the ciliary body.” The authors surmised that evidence of CB1 receptors in the “ciliary pigment epithelium suggests that cannabinoids may have an effect on aqueous humor production.” CB1 presence in the trabecular meshwork and Schlemm’s canal “suggests that cannabinoids may influence conventional outflow.” Evidence of effects on uveoscleral outflow are inferred by CB1in the ciliary muscle.
CB1 receptors are also present on the other (back) end of the eye, the all important retina and its attachment to the optic nerve with retinal ganglion cells. Here, the neuroprotective effects of activation of cannabinoid receptors may prevent and reduce damage caused by high IOP. Research out of Finland concluded that “at least some cannabinoids may ameliorate optic neuronal damage through suppression of N-methyl-D-aspartate receptor hyperexcitability, stimulation of neural microcirculation, and the suppression of both apoptosis and damaging free radical reactions, among other mechanisms.”
Research our of University of Aberdeen, UK remind that not all neuroprotective properties of cannabinoids come from their activation of the endocannabinoid system; cannabinoids are powerful antioxidants in their own right. Writing in the British Journal of Ophthalmology, the researchers note that “Classic cannabinoids such as Δ9-THC, HU-211, and CBD have antioxidant properties that are not mediated by the CB1 receptor. As a result, they can prevent neuronal death by scavenging toxic reactive oxygen species produced by overstimulation of receptors for the excitatory neurotransmitter, glutamic acid.” The British researchers also note that regarding the CB2 receptor, “The anti-inflammatory properties of CB2 receptor agonists might also prove to be of therapeutic relevance in different forms of inflammatory eye disease.”
Tragically, little of this research has been done in the USA. Even though glaucoma blinds hundreds of thousands of Americans each year, the anti-cannabis bias of the controlling agencies (DEA, NIDA ) has not allowed research with this natural plant substance that can prevent these blindings. They cling to the fiction (and blatant lie) that marijuana has no medical value and disallow all research even while their countrymen and women needlessly lose precious, precious sight.
So strong is this prejudice that even so-called advocacy groups such as the Glaucoma Research Foundation appear uninterested in a natural substance that helps prevent glaucoma. “Information” on medical marijuana at this site appears to have been written by the propaganda officers of the DEA.
Meanwhile, across the globe, research moves forward identifying evermore ways humans can gain health benefits from the cannabis plant. At the forefront are the IOP lowering, optic nerve-protecting effects of THC and other cannabinoids.