The 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 gradually increases, causing increasing damage to the optic nerve, and gradual deterioration of vision. 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 painfull deterioration to blindness that is otherwise enevitable. 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-vasculat system. 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 water soluble.