Phytochemicals and Cannabinoids from Cannabis Spp. implicated in the treatment Glaucoma

Glaucoma is a group of ocular disorders that constitute the leading cause of irreversible blindness worldwide. Globally it is estimated that 8.4 million people are blind as a result of glaucoma. This number is set to increase to approximately 11.2 million by 2020.

Glaucoma is characterized by an increase in intraocular pressure which may lead to optic nerve damage and eventual blindness if left untreated.  Glaucoma may be closed angled or open angled. Closed-angle glaucoma has a sudden onset of action and is characterized by pain, while the term open-angle glaucoma (OAG) causes progressive damage to the optic nerve and painless loss of vision if left untreated. The highest prevalence of open-angle glaucoma occurs in Africans and is estimated to affect approximately three percent of Jamaicans.

Smoking ganja has long been known to cause vasodilation and ocular hypotension, however the identification of CB1 receptors on the eye allow for topical application of THC and CBD. In addition recent studies have shown that glaucoma patients generally have low anandamide levels. Anandamide is one of the body’s natural cannabinoids.

Mechanisms of action postulated for THC on the eye

  1. Effect of decrease in intraocular pressure by a direct action on CB1 receptors on the eye causing reduced ciliary pressure resulting in changes in aqueous humour.
  2. Activation of the prostaglandin E2 receptor after conversion to prostamides. Prostamides are oxidation derived products of the endocannabinoid, anandamide resulting in increased uveoscleral outflow and a lowering of intraocular pressure.
  3. THC and CBD have neuroprotective action on the eye. High levels of glutamate have been found in glaucoma patients. Increased glutamate levels lead to neurotoxicity and eventual cell death and irreversible blindness.  THC and CBD prevent glutamate induced neurotoxicity via action on CB1 receptors.

Cannabigerol (CBG) has also shown a reduction in intraocular pressure without adverse effects after long term use.

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