Glaucoma is a disease of the major nerve of vision, called the optic nerve.
The optic nerve receives light-generated nerve impulses from the retina and transmits these to the brain, where we recognize those electrical signals as vision. Glaucoma is characterized by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.
Glaucoma is usually, but not always, associated with elevated pressure in the eye (intraocular pressure). Generally, it is this elevated eye pressure that leads to damage of the eye (optic) nerve. In some cases, glaucoma may occur in the presence of normal eye pressure. This form of glaucoma is believed to be caused by poor regulation of blood flow to the optic nerve.
The eye’s rigid shape is normally maintained in part by IOP (intraocular pressure). Since a high IOP is the only known major risk factor for glaucoma that can be controlled, most treatments are designed to reduce IOP. Marihuana can reduce IOP when taken orally or by inhalation, but not when administered topically. While a reduction in IOP slows the rate of glaucoma symptom progression, there is no direct evidence of benefits of marihuana in the natural progression of glaucoma. Also, the reduction only lasts for a few hours, and it is not known how marihuana interacts with other drugs used to treat glaucoma.