Medical Marijuana in the Treatment of Glaucoma
The human eyeball is filled with fluid, which exerts pressure to keep the eyeball spherical. Glaucoma is a condition in which the channels through which the fluid flows gradually become blocked and the pressure in the eyeball gradually increases. This causes progressive damage to the optic nerve, and gradual deterioration of vision. Glaucoma is the second leading cause of blindness, and affects 1.5 % of 50-year olds and 5 % of seventy-year olds.
Standard treatments have unpleasant or dangerous side effects, and have little effect on intraocular pressures in end-stage glaucoma. Cannabis however lowers intraocular pressures dramatically with none of the serious side effects. Patients who find that standard medicines do not help their conditions report that smoking cannabis quickly restores their vision. Many long-term glaucoma patients have successfully maintained their sight for over 20 years, using cannabis, and avoided the gradual painful deterioration leading to blindness that is otherwise enevitable. (Ironically the discovery that cannabis lowers intraocular pressure was made accidentally during a police experiment. They were trying to discover if cannabis caused pupil dilation in users, so that they could detect and arrest them more easily!)
It is possible that a cannabis-containing eyedrop could be developed in the future which would have no side effects but this is made difficult since cannabinoids are not water soluble.
The effect of cannabis on intraocular pressure (IOP) in normal subjects has been well studied, however the effect on glaucoma patients is less well known, with only a handful of patients studied. Only one study used herbal cannabis, the rest have used cannabinoids. Hepler & Frank (1971) found that oral or smoked cannabis reduced intraocular pressures in normal subjects for about 4 to 5 hours with “no indications of any deleterious effects … on visual function or ocular structure”. They concluded that cannabis may be more useful than conventional medications and probably works by a different mechanism.
Almost all of the studies using cannabinoids have been double-blind and placebo controlled. Two studies were of the effects of oral or smoked THC on IOP in normal subjects. Hepler et al. (1976) reported that the drop in IOP was dose-related. Jones et al. (1981) found that tolerance to the effects quickly built up, and there was a rebound in IOP to above baseline levels when treatment was stopped. Another two studies used intravenous infusions of various cannabinoids. Perez-Reyes et al. (1976) found that only the cannabinoids that had psychoactive effects produced a drop in IOP. Cooler & Gregg (1977) reported a drop in IOP but increased anxiety. The effects of cannabinoids on IOP were confirmed in numerous animal experiments, reviewed by Adler & Geller (1986).
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