Glaucoma is a group of diseases that damage the eye's optic nerve, and can sometimes result in loss of vision or blindness. The most common cause of nerve damage is high pressure fluid build-up inside the eye. Current treatments improve the flow of fluid, which decreases pressure and damage to the nerve.
Glaucoma and Your Endocannabinoid System
Medical Cannabis Guidelines
Cannabinoids are difficult to apply topically to the eye because they are not water soluble, so they do not absorb well into the eye. However, there is work being done to develop THC eye drops that do absorb effectively.  Currently, to control eye pressure, dosing every 3-4 hours is best if possible. To keep eye pressure at safe levels at all times, a combination of long-acting prescription medications and cannabis may give the best results.
Start low and go slow to avoid uncomfortable intoxication with THC.