Glaucoma Editorial

GLAUCOMA EDITORIAL

Efficacy in Glaucoma Treatment---The Potential of Marijuana

ANNALS OF OPHTHALMOLOGY---April 1980 449-50

Years of clinical experience wit the conventional glaucoma drugs
have proven their efficacy. Miotics, epinephrine compounds, and carbonic
anhydrase inhibitors are clearly effective in lowering intraocular
pressure. In addition, their efficacy in preserving visual function has
been demonstrated, mainly through clinical experience; numerous anecdotal
accounts have shown interruption, or reversal, of progressive visual field
loss at the time treatment with these drugs was started. Isolated,
uncontrolled studies support these accounts (1).

Numerous other medications and compounds have been studied over the
years to determine if they are beneficial for the glaucoma patient. Most
of these prospective new glaucoma drugs are compounds which interact with
the sympathetic innervation of the eye, and some have been shown to lower
intraocular pressure effectively. For example, in Europe, for several
years, clonidine (Catapres) was used topically to treat glaucoma, because
it caused the intraocular pressure to be lower. Now, clinical use of this
drug appears to have been discontinued, because studies of laboratory
animals showed reduced optic nerve vascular perfusion after clonidine (2)
and acute, uncontrolled clinical studies showed no improvement of visual
field defects in patients with otherwise adequate lowering of intraocular
pressure (3).

Marijuana plant material, and several of the approximately 20
active cannabinoid components found in the plant, have been demonstrated to
lower intraocular pressure in laboratory animals when administered by
several routes (4) and have been shown to lower intraocular pressure in a
majority of treated normal human volunteers and glaucoma patients (5). The
mechanism of action is not understood completely, there appear to be both
ocular and central nervous system components (4). Recent reviews and an
editorial have summarized the status of studies of the intraocular pressure
lowering effect of the cannabinoids (4,6,7).
While the intraocular pressure effect is important---no new drug
has yet been shown to be good for glaucoma patients without this
effect---most reports of studies of potential new drugs for glaucoma lack
information about whether visual function is preserved during treatment.

The clonidine experience suggests that vascular perfusion pressure
is important for preservation of visual function in glaucoma (2).
Marijuana may reduce perfusion pressure. One of 10 young normal volunteers
given an acute intravenous dose of 0.022 mg/kg of
delta-9-tetrahydrocannabinol (about 1.5 mg total dose) developed
hypotension to the range of 80/40, with associated pre-syncopal symptoms
after 0.044 mg/kg (about 3.0 mg total dose) of the drug (8). Thus,
marijuana may lower intraocular pressure without preventing visual
impairment in glaucoma patients. These observations emphasize the need for
controlled clinical trials with marijuana and its derivatives to evaluate
their effects upon both intraocular pressure and the preservation of visual
function in the glaucoma patient. Side-effects should be recorded
simultaneously. This need was emphasized by the recent announcement that
the National Eye Institute is seeking research grant applications on
cannabinoids in the treatment of glaucoma (9). These clinical trials can
be undertaken without altering existing laws or the existing classification
of marijuana and its derivatives as controlled substances in Schedule I.
Obviously, the compound being studied would have to conform to guidelines
for investigational new drugs. The public will be better served, and
patients may be spared unnecessary risks, if results of these studies can
be available before marijuana and its derivatives are used for
compassionate or routine treatment.

Douglas E. Gaasterland, MD
Clinical Branch
National Eye Institute
National Institutes of Health
U.S. Department of Health, Education & Welfare
Bethesda, Maryland 20205

References

1. Phelps CD: Visual field defects in open-angle glaucoma: progression
and regression. Docum Ophthalmol Proc Series volume 19. Edited by Dr. W.
Junk by Publishers. The Hague-Boston-London, 1979, pp. 187096.

2. Bill A. Heilmann K: Ocular effects of clonidine in cats and monkeys
(Macaca iris). Exp Eye Res 21: 481, 1975

3. Heilmann K: Progression and regression of visual field defects. In
Glaucoma. Conceptions of a Disease. Edted by K Heilmann and KT
Richardson. Philadelphia-London-Toronto, W.B. Saunders, Inc., 1978, pp.
171-175.

4. Green K: The ocular effects of cannabinoids. In Current Topics in Eye
Research. Edited by JA Zanunaisky and H Davson. New York, Academic Press,
1979, p. 175.

5. Hepler RS, Frank IM, Petrus R: Ocular effects of marijuana smoking.
In Pharmacology of Marijuana. Edited by MC Braude and S. Szara. New York,
Raven Press, 1976, p. 815.

6. Goldberg I, Kass MA, Becker B: Marijuana as a treatment for glaucoma.
The Sightsaving Review 48: 147-155, Winter '78/'79

7. Green K: Glaucoma Editorial: Marijuana in ophthalmology-past,
present, and future. Annals of Ophthalmol 11: 203-205, 1979

8. Cooler P, Gregg JM: The effect of delta-9-tetrahydrocannabinol on
intraocular pressure in humans. In the Therapeutic Potential of Marijuana.
Edited by S Cohen and RC Stillman. New York-London, Plenum Medical Book
Company, 1976, p. 77

9. NIH Guide for Grants and Contracts. Volume 7, No. 18, November 27,
1978, p. 21

Glaucoma Editorial is supported by Lederle Laboratories as a continuing
service to ophthalmology.


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