What is Glaucoma?

The optic nerve carries signals from the eye to the brain, resulting in vision. Glaucoma can lead to damage of the optic nerve, and untreated, long-standing glaucoma can lead to blindness. In many cases, this damage is caused by an increase in pressure within the eye (intra-ocular pressure), resulting from abnormalities with the amount of fluid in the front portion of the eye, called “aqueous humor“, which is produced by a part of the eye called the ciliary body.

Pressure in the eye builds either due to (1) a decrease in aqueous humor clearance due to a blockage in the outflow space, or (2) an increase in the amount of aqueous humor in the front eye compartment. For example, when blood pressure is high, the pressure in the capillaries of the ciliary body may also be high, leading to increased production by ultrafiltration/decreased absorption of aqueous humor, leading to an increase in liquid and, subsequently, pressure.

Glaucoma ranks among the most frequently cited reasons for using medical marijuana and is one of the indications for which the federal government once granted permission for compassionate marijuana use (see Chapter 2 and Chapter 11). Research findings from as early as the 1970s show that both marijuana and THC reduce intraocular pressure, a key contributor to glaucoma. The first such reports generated considerable interest because at the time conventional medications for glaucoma caused a variety of adverse side effects. But, as will be described, other treatments for the disorder have since eclipsed marijuana-based medicines. Conventional therapies for intraocular pressure outperform cannabinoids, and the next generation of glaucoma drugs is expected to treat the disease more directly or even reverse its progress.

Over the past year, media coverage and national awareness of the legalization of marijuana for medical and recreational use have increased. Twenty-one states plus Washington, DC, have enacted laws that allow the use of medical marijuana with a doctor’s recommendation, and two of those states—Colorado and Washington—have legalized marijuana for recreational use.1 It is therefore important that eye care providers learn about medical marijuana for glaucoma therapy. This article reviews some of marijuana’s effects on the eye.