Glaucoma, the number two cause of blindness in the United States, is characterized by a dangerous increase of the fluid pressure within the eye. Glaucoma patient Robert Randall was the first person to ever receive federal approval for the use of cannabis after pioneering the medical necessity defense in Florida in 1976.  Although the American Academy of Ophthalmology has strongly opposed the use of cannabis to treat glaucoma, the effectiveness of cannabis in relieving intraocular pressure has been demonstrated by numerous clinical trials, including those of the National Academy of Sciences. One study indicate that two cannabinoids, delta-8 THC and CBN, effectively reduced intraocular pressure, but that two others, CBD, and delta-9 THC, the psychoactive ingredient of Marinol, did not. 
One major objection to cannabis use for the treatment of glaucoma is the apparent decrease in intraocular fluid.  Another major objection is the relative duration of action. While cannabis is shown to be as effective at reducing intraocular pressure as other medications, the dose level must be maintained at three- or four-hour intervals, while other medications may be taken less frequently.
Scientists remain tantalized by the possibility of studying the effects of cannabinoids and of synthesizing more effective cannabinoid derivatives.  Although the medical application of cannabis is not endorsed by the American Society of Ophthalmology  or the Institute of Medicine, and while the exact mechanism is not thoroughly understood, at least some physicians have the vision f Lester Grinspoon, M.D., who testified before Congress in 1977, “Cannabis does not cure the disease, but it can retard the progressive loss of sight when conventional medication fails and surgery is too dangerous.” 
Cannabinoid eye drops have decreased the ocular pressure of mice, but as of yet have not been found as effective in several human trials. , , 
Related sections: Psychoactivity.
 Randall, ed. Affidavit before Administrative Law Judge Francis L. Young of the US Drug Enforcement Administration, Marijuana Medicine and the Law. Washington, DC: Galen Press, 1988
 Alliance for Cannabis Therapeutics, P.O. Box 19161, Sarasota, FL 34276
 Merritt, Perry, Russell, and Jones, “Topical delta-9-tetrahydrocannabinol and aqueous dynamics in glaucoma.” Journal of Clinical Pharmacology, (8-9 Suppl) pp.467S-471S, August 21, 1981
 Finn, “Cannabinoid investigations entering the mainstream.” The Scientist, Vol. 12, No. 3, pp. 1-8, February 2, 1998
 Randall, ed. op. cit.
 Summary of the Testimony of Lester Grinspoon, MD before the Crime Subcommittee of the Judiciary Committee, U.S. House of Representatives, October 1, 1997
 Merritt, Perry, Russell, and Jones, op. cit.
 Green and Roth, “Ocular effects of topical administration of delta-9-tetrahydrocannabinol in man.” Archives of Ophthalmology. Vol. 100, No. 2, pp. 265-267, February 1992
 Jay and Green, “Multiple-drop study of topically applied 1% delta-9-tetrahydrocannabinol in human eyes.” Archives of Ophthalmology, Vol. 101, No. 4, pp. 591-593, April 1993