According to the World Health Organisation (WHO), there are more than 1 billion people living with vision impairment such as short and far sightedness, glaucoma and cataract.  In most cases, these could have easily been prevented or treated with cataracts operation, access to glasses, or access to economical health care. However, a report states that stronger integration of eye care is needed within national health services, through prevention, early detection, treatment and rehabilitation. Today we want to analyze if medical cannabis can be useful in the treatment of glaucoma.

What is glaucoma?

Glaucoma is caused by abnormally high intraocular pressure (IOP).  IOP is the fluid pressure inside the eye.  Due to the high pressure, the retina and the optic nerve leads to the process of losing vision.[1]

It can be undiagnosed in 9/10 people who are affected globally in which 50% of those are in developed countries.  Therefore, detection of this disease should be improved. Glaucoma is thought to be present only when at least one eye has both optic disc damage and visual field loss. The combination of this damage can sufficiently indicate the death of a substantial number of retinal ganglion cells and loss of the optic nerve.[2]

Endocannabinoid system in the eye

The endocannabinoid system (ECS) is present in the eye in both anterior and posterior ocular tissues including the retina, the ciliary body, trabecular meshwork and Schlemm’s canal.  The ECS include cannabinoid receptors, cognate degradative  and biosynthetic enzymes (proteins), and endocannabinoids, such as anandamide (AEA) and 2- arachidonoylglycerol (2-AG). The presence of all these components supports an important role for the ocular function such as reduced tear production and reduction in IOP.

Is there treatment for glaucoma?

Long term effects of cannabinoids on glaucoma

Traditional treatment includes prescribing medications, going through laser treatments or even surgery. These approaches normally require treatment over decades, therefore any medical cannabis designed must be safe and effective when administering to those who are confirmed to be diagnosed with glaucoma.[3]To date, studies evaluating the effectiveness of medical cannabis in long-term use have had mixed results. Most studies have reported loss of effect of IOP lowering properties within a matter of hours. However, a study by Hosseini and his colleagues found that chronic topical application of 0.5% WIN 55,212-2 (synthetic THC) was effective in reducing IOP for 1 month in rats.3

Moreover, a different research from 2018 has shown that endocannabinoid system may not only reduce eye pressure but can also act on certain receptors to act as a neuro-protecter against damage to the optic nerve.  [4]  However, this is no news as a study in 2009 showed how cannabinoids receptors (CB1 and CB2) expression are involved in survival and death, in retinal cells. [5]

With more research dedicated to this, it can have the potential to prevent glaucoma or other retinal neurodegenerative diseases.

Regardless, the Canadian Ophthalmological Society does not support the medical use of cannabis for the treatment of glaucoma due to the short duration of action, the incidence of undesirable psychotropic and other systemic side effects, and the absence of scientific evidence showing a beneficial effect on the course of the disease”.[6]

World Glaucoma Day

World Glaucoma Day is celebrated on the 12th of March, but awareness week in 2020 takes place from 8th to 14th March.

In conclusion, while there have been studies proving that cannabis has certain properties that could help (as an adjuvant treatment) prevent glaucoma, more investigation has to be carried out in order to fully find a viable treatment for glaucoma, dosing and to avoid any adverse effects.

[1] Tomida, I. (2004). Cannabinoids and glaucoma. British Journal of Ophthalmology, 88(5), 708–713. doi:10.1136/bjo.2003.032250

[2] Quigley, H. A. (2011). Glaucoma. The Lancet, 377(9774), 1367–1377. doi:10.1016/s0140-6736(10)61423-7

[3] Cairns, E. A., et alt. (2016). The Endocannabinoid System as a Therapeutic Target in Glaucoma. Neural Plasticity, 2016, 1–10. doi:10.1155/2016/9364091doi:10.2174/1570159X15666170724104305

[4] Rapino C, et alt. Neuroprotection by (endo)Cannabinoids in Glaucoma and Retinal Neurodegenerative Diseases. Curr Neuropharmacol. 2018;16(7):959-970. doi:10.2174/1570159X15666170724104305

[5] Yan Wei et al. Presence and regulation of cannabinoid receptors in human retinal pigment epithelial cells. Mol Vis. 2009; 15: 1243–1251.

[6] Rafuse, P., & Buys, Y. M. (2019). Medical use of cannabis for glaucoma. Canadian Journal of Ophthalmology, 54(1), 7–8. doi:10.1016/j.jcjo.2018.11.001