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Medical Marijuana as a Treatment for Glaucoma

June 26, 2014

Norberto Mancera BS, Binna M Chokshi MD, and Hershel R Patel MS MD

University of South Florida - Morsani College of Medicine

Glaucoma is one of the leading causes of blindness in the world, which ophthalmologists find frequently in their patient population. Defined as an increase in intraocular pressure (IOP), Glaucoma causes retinal ganglion or nerve cell death over time leading to visual field defects. These defects are often silent and lead to progressively worsening "tunnel vision". Treatments are limited to several combinations of anti-glaucoma medications such as beta-blockers, alpha-agonists, miotics, carbonic anhydrase inhibitors, and prostaglandins. Further invasive options include laser and/or surgical treatments.

In more recent times, medical marijuana has found a spot light in media and political discussions, with advocates arguing its benefits for treating chronic pain, nausea, anorexia and glaucoma in the hopes of legalization. For several decades it has been suggested that cannabis and similar compounds can be beneficial in decreasing IOP. Hepler et al. in 1971 even determined that cannabinoids can be linked to the reduction of IOP. Multiple others have expanded on his work discovering that there are in fact, cannabinoid receptors in the eye. However, the mechanism of action by which cannabinoids reduce IOP is unknown.

There are multiple theories including stimulation of cannabinoid receptors present on ciliary epithelium, ciliary body muscles and vessels, trabecular meshwork and Schlemm's canal. These theories suggest that by stimulation of receptors at these sites, there is a decrease in aqueous fluid production and an increase in outflow - leading to a decrease in IOP - a potential treatment for glaucoma. Another possible benefit shows that cannabinoids independently prevent damage to optic nerve. These benefits lead to the multiple studies testing the theory of treating glaucoma with marijuana.

Marijuana is preferentially consumed by smoking. However, smoking is not the best method of delivery for individuals solely seeking the medical benefits of this compound. Further, considering the chronic nature of glaucoma, this would lead to prolonged smoking for medicinal purpose but with undesired effects. These side-effects would include chronic exposure to carcinogenic agents and emphysematous-like lung diseases. Additionally, this compound has well-known psychedelic side effects.

This leads to the concern of finding an effective and efficient way of delivering the drug into the system with therapeutic effects only in the eye. Researchers started to experiment with oral and topical methods of application. A randomized double-blind placebo study was conducted using sublingual spray with three-whole-plant cannabis-based extracts. The purpose was to test for the effect on IOP; focusing on safety, tolerability and side effects. The study was successful in demonstrating that dealta-9-THC is capable of reducing IOP, however, it was also responsible for psychedelic side effects. Hence, the next logical option was sorted - topical use - localize to the site of disease and reduce side effects. This approach uses cannabinoids in eye drop format. The method showed promise because it was readily absorbed in the eye. Unfortunately, extended use produced ulcers leading to corneal damage.

Added to the above-mentioned complications of administration, the question of dosing and practicality arises. This compound's generation of IOP lowering effects is very short-lived at approximately 3 to 4 hours. Given the chronicity of glaucoma and the need to maintain normal IOP at all hours, plus twenty-four hours in a day, the medicine would be dosed for 6 to 8 times every day for the rest of the patient's life. This means that the patient would have to wake up in the middle of night to maintain compliance, a particularly difficult routine to follow. In addition, a missed dose would risk optic nerve damage, which could lead to vision loss. Also, being dosed that often would increase the psychedelic side effects, interfering with the patient's daily activity.

Internationally speaking, both the Canadian and Indian Ophthalmology Associations have given a negative recommendation to use marijuana and derivatives as a treatment for glaucoma. Marijuana has numerous other compounds that haven't been studied or are unknown to scientists. Advocates may continue their efforts for legalization and it may serve a purpose for treatment of other medical conditions. However, the use of marijuana does not seem practical in treating this prevalent cause of blindness, Glaucoma.


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