Cannabis

Studies in the 1970s reported that the use of cannabis may lower intraocular pressure. In an effort to determine whether marijuana, or drugs derived from it, might be effective as a glaucoma treatment, the US National Eye Institute supported research studies from 1978 to 1984. These studies demonstrated some derivatives of marijuana lowered intraocular pressure when administered orally, intravenously, or by smoking, but not when topically applied to the eye.

In 2003, the American Academy of Ophthalmology released a position statement stating that cannabis was not more effective than prescription medications. Furthermore, no scientific evidence has been found that demonstrates increased benefits and/or diminished risks of cannabis use to treat glaucoma compared with the wide variety of pharmaceutical agents now available.

In 2012 the American Glaucoma Society published a position paper discrediting the use of cannabis as a legitimate treatment for elevated intraocular pressure, for reasons including short duration of action and side effects that limit many activities of daily living.

1. "Marijuana and Medicine: Assessing the Science Base". Nap.edu. Retrieved 2014-02-20.
2. "Marijuana and Medicine: Assessing the Science Base (1999), Institute of Medicine, National Academies Press". Nap.edu. 
3. "Complementary Therapy Assessment: Marijuana in the Treatment of Glaucoma". American Academy of Ophthalmology. Retrieved 2011-05-04.
4. "Complementary Therapy Assessments : American Academy of Ophthalmology". One.aao.org. Retrieved 2011-01-24.
5. Jump upJampel, Henry (2010). "American Glaucoma Society Position Statement: Marijuana and the Treatment of Glaucoma". J Glaucoma. 19 (2): 75.

Marijuana and Cannabinoids in Glaucoma

Marijuana and THC have been shown to reduce IOP by an average of 24% in people with normal IOP who have visual-field changes. In a number of studies of healthy adults and glaucoma patients, IOP was reduced by an average of 25% after smoking a marijuana cigarette that contained approximately 2% THC—a reduction as good as that observed with most other medications available today.1^{,16,32,76,77,125,193} Similar responses have been observed when marijuana was eaten or THC was given in pill form (10-40 mg) to healthy adults or glaucoma patients.76^,91 But the effect lasts only about three to four hours. Elevated IOP is a chronic condition and must be controlled continuously.

Intravenous administration of D⁹-THC, D⁸-THC, or 11-OH-THC to healthy adults substantially decreased IOP, whereas cannabinol, CBD, and b-OH-THC had little effect.31^,146 The cause for the reduction in IOP remains unknown, but the effect appears to be independent of the frequently observed drop in arterial systolic blood pressure (Keith Green, Medical College of Georgia, personal communication).

Three synthetic cannabinoids were investigated; BW29Y, BW146Y, and nabilone. They were given orally to patients who had high IOP. BW146Y and nabilone were as effective as ingesting THC or smoking

*The cornea and lens must be optically clear, which means that there cannot be blood circulation in these tissues. The aqueous humor is a clear fluid that functions as alternative circulation across the rear of the cornea and to the lens, providing nutrients and removing waste from these tissues.

marijuana but again with a very short duration of action; BW29Y was ineffective. 136,182

Topical treatments with cannabinoids have been ineffective in reducing IOP. When D⁹-THC was applied topically as eye drops, whether once or four times a day, there was no decrease in IOP.60^,90 Suspensions of lipophilic THC tended to be irritating to the eye.

In summary, cannabinoids and marijuana can reduce IOP when administered orally, intravenously, or by inhalation but not when administered topically. Even though a reduction in IOP by standard medications or surgery clearly slows the rate of glaucoma symptom progression, there is no direct evidence of benefits of cannabinoids or marijuana in the natural progression of glaucoma, visual acuity, or optic nerve atrophy.^92,115

In addition to lowering IOP, marijuana reduces blood pressure and has many psychological effects. Merritt and co-workers reported hypotension, palpitations, and psychotropic effects in glaucoma patients after inhalation of marijuana.125 Cooler and Gregg31 also reported increased anxiety and tachycardia after intravenous infusion of THC (1.5-3 mg). All those side effects are problematic, particularly for elderly glaucoma patients who have cardiovascular or cerebrovascular disease. The reduction in blood pressure can be substantial and might adversely affect blood flow to the optic nerve. ²⁴ Many people with systemic hypertension have their blood pressure reduced to manageable and acceptable levels through medication, but this does not seem to affect their IOP. In contrast, there is evidence that reduction in blood pressure to considerably below-normal levels influences IOP and ocular blood flow.46^,74,142 Hence, in the case of an eye with high IOP or an optic nerve in poor condition and susceptibility to high IOP, reduced blood flow to the optic nerve could compromise a functional retina and be a factor in the progression of glaucoma.

Because it is not known how these compounds work, it is also not known how they might interact with other drugs used to treat glaucoma. If the mechanism involves a final common pathway, the effects of cannabinoids might not be additive and might even interfere with effective drugs.

https://www.nap.edu/read/6376/chapter/6#174

https://www.nap.edu/read/6376/chapter/6#175