human eyeball is filled with fluid which exerts pressure to keep the eyeball
spherical. Glaucoma is a condition where the channels through which the
fluid flows gradually become blocked, and the intraocular pressure (IOP)
gradually increases causing increasing damage to the optic nerve and gradual
deterioration of vision. Glaucoma is the second-largest 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 using cannabis for 20 or 25 years, and avoided the gradual painful deterioration to blindness that is otherwise inevitable.
However older generations, who are most at risk of glaucoma do not appreciate the euphoric side effects of smoked or ingested cannabis. There is also concern about the effects on the cardio-vascular system. These disadvantages are especially significant when one takes into account that a dose of cannabis needs to be taken about every 4 hours for the full benefits to occur.
There is hope 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 naturally water soluble. However, animal experiments have taken place using THC dissolved in oil to aid its solubility, which have shown benefits without any of the afore-mentioned side-effects.
Whilst cannabinoids are known to lower IOP it is not currently known how they achieve this. There have been no conclusive tests to determine the mechanism of action, or even if the effect is achieved by brain-receptor interaction (as is the psychoactivity of cannabis). If the effect is achieved through CB2 receptors, then more specific cannabis-based medications could be developed that do not have any unwanted effect on the Central Nervous System. It is also of course possible that the medical effects work through an entirely different route and are not receptor-based. The uncertainty of cannabis' course of action in lowering IOP implies that it is also unknown whether or not it works in the same way as current medications do. If the mechanism of action differs from existing therapies then it is likely to be able to be used with other medications to provide additional benefits that wouldn't be seen if either medication was taken separately.
Several synthetic cannabnioids, including Nabilone, have been tested for the treatment of glaucoma with differing results in terms of efficacy to the condition and side-effects. Synthesised and isolated cannabinoids seem worthy of further investigation. It is feasible that future research could lead to the development of a drug based on cannabis which has fewer side effects and doesn't require such frequent dosing than THC alone. In addition, reducing IOP is not necessarily the only way to help glaucoma sufferers. More direct action on blood flow and neural protection may be of benefit. Researchers have studied a synthetic cannabinoid which is thought to provide some degree of neural protection.
Despite the possible drawbacks, one should be reminded that using cannabis evidently does some glaucoma sufferers a lot of good. 2 out of the 8 patients who are legally permitted to use cannabis medicinally in the US have used government-supplied cannabis for over 10 years to maintain their sight. It seems cruel to prohibit and, indeed, punish the huge numbers of glaucoma sufferers that could be helped by cannabis. Following a review of existing research, the Australian National Task Force on Cannabis concluded that it would not be desirable to criminalise such users.
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.