Julie Gardener
New Member
GLAUCOMA, HYPERTENSION, AND MARIJUANA
John C. Merritt, MDChapel Hill, North Carolina
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 74, NO. 8,1982
The glaucomas are characterized by increased intraocular pressure resulting in damage to the optic nerve. Concomitant ocular pathology that can frequently result in increased pressures are due to: (1) fibrovascular membranes; (2) inflammatory closure by synechiae; (3) trauma, either social or surgical; (4) trabecular obstruction (blood, macrophages, alpha-chymatrypsin); (5) lens induced glaucomas; and (6) corneal endotheliopathy-atrophic iris syndromes. The primary glaucomas are either of the open or closed-angle varieties. Primary open-angle glaucoma, the most common variety, is characterized by (1) increased pressures within the eye (increased ocular tension, OT); (2) pressure-related visual field defects1' 2; and (3) optic nerve pallor and atrophy.
No good epidemiological data exist on the prevalence of open-angle glaucoma. In 1978 a cohort study from Framingham, Massachusetts, suggested that 3 percent of this 99.4 percent Caucasian population has open-angle glaucoma.3 Although there are no data on blacks, the National Eye Institute suggested that data retrieved from a model reportingarea (22 states in 1970) suggested that open-angle glaucoma blinded three to five times more nonwhites than whites.4
Open-angle glaucoma treatment traditionallyhas been medical in the United States. Data gathered over ten years in Cambridge, England, have inferred that primary surgical interventions may be more effective in open-angle glaucoma.5 The medical therapies include eye drops (miotics, aqueous inflow inhibitors) and systemic carbonic anhydrase inhibitors. Topical beta adrenergic blockers (timolol), epinephrine and its pro-drug (dipivefrin hydrochloride) all lower ocular tension by decreasing aqueous formation. The miotics, however, lower ocular tension by increasing aqueous outflow from the anterior chamber. Blacks respond less favorably to miotics,6'7 epinephrine8 and timolol,9 than whites. Similarly, surgical procedures designed to lower ocular tension by aqueous drainage from the anterior chamber (filtering operations) have significantly higher failure and complication rates among blacks than in whites. 1012 Therefore, any ocular hypotensive agent should receive clinical trials not only in these various types of glaucomas, but also in various population subsets.
Mexican marijuana, containing 1.8 to 2.8 percent A9 tetrahydrocannabinol (A9 THC), has consistently been shown to lower both intraocular pressure and blood pressure in both open-angle glaucoma13 and heterogenous glaucoma.14'15 The decreased ocular tension results from decreased aqueous production mediated through the pressuredependent portion of aqueous formation (ultrafiltration). Characteristically, marijuana induces a tachycardia within 5 to 10 minutes, which is invariably followed by decreased blood and intraocularpressures. The maximum ocular hypotensive effect of 25 to 30 percent occurs between 60 and 90 minutes.
Cardiovascular changes generally return to baseline with 3'/2 hours; but ocular hypotensive responses often persist longer.15 Sudden precipitous falls in systolic blood pressure have occurred in 18 percent of marijuana-naive subjects inhaling Mexican marijuana. These syncopal-like episodes were characterized by sudden falls in blood pressure, lightheadedness, a faint, and thready pulse often accompanied by nausea and bradycardia. Positioning the subject in a reclining position invariably alleviated these signs. This postural hypotension was not related to plasma A9 THC levels, previous marijuana experience, or inhalation techniques.16 A similar episode of postural hypotension and dysphoria occurred 1 hour after the ingestion of 5 mg of oral A9 THC in a 52-year-old black woman with both essential hypertension and open-angle glaucoma. Although our studies would indicate that 5 mg of oral A9 THC are inactive in heterogenous glaucoma, this case may represent a certain sensitivity of the hypertensive glaucoma patient to the peripheral dilatory effects of A9 THC. 17
Hypertensive subjects have consistently been shown to receive a more substantial lowering of the blood pressure and intraocular pressure when compared to normotensive glaucoma populations.18'19 Similarly, topical 0.1 percent A9 THC in light mineral oil vehicles decreased the systolic blood pressure 12.8 mmHg (in 8 hypertensive glaucoma subjects) after unilateral topical applications.19 The maximum hypotensive effect in both treated and untreated eyes after unilateral topical A9 THC has repeatedly been shown to occur at 6 hours with significant ocular hypotensive effects persisting for 8 to 12 hours in both animal and human studies.19'20 It is known that the contralateral decrease of ocular tension in fellow untreated eyes after topical A9 in light mineral oil vehicle results from decreased aqueous production.21 Less well demonstrated are the possible cardiac and/or central nervous system mechanisms involved in aqueous dynamics. Systemic A9 THC therapies invariably produce a decreased perfusion pressure to the eye. This decreased perfusion to an already damaged optic nerve may not be of long-term benefit to glaucoma victims, although it maywell treat their concomitant essential hypertension. Therefore, other cannabinoids which mayexert a pressure lowering effect locally within the eye should become the focus of present glaucoma research.
Literature Cited
1. Armaly MF. The visual field defect and ocular pressure level in open-angle glaucoma. Invest Ophthalmol 1969; 8:105-124.
2. Heilmann K. On the reversibility of visual field defects in glaucomas. Trans Am Acad Ophthalmol Oto 1974; 78:304-308.
3. Kini MM, Leibowitz HM, Colton T, et al. Prevalence of senile cataract, diabetic retinopathy, senile macular degeneration and open angle glaucoma in the Framingham Eye Study. Am J Ophthalmol 1978; 85:28-34.
4. Moorhead HB, Kahn HA. Statistics on blindness in Model Reporting Area, 1969-1970. DHEW (NIH) 73-417. Government Printing Office, 1973.
5. Watson PG, Grierson I. The place of trabeculectomy in treatment of glaucomas. Ophthalmology 1981; 88:175-196.
6. Krill AE, Newell FW. Effects of pilocarpine on ocular tension dynamics. Am J Ophthalmol 1964; 57:34-41.
7. Harris LS, Galin MA. Effect of ocular pigmentation on ocular tension dynamics. Am J Ophthalmol 1971; 72:923-925.
8. Melikian HE, Lieberman TW, Leopold IH. Ocular pigmentation and pressure outflow response to pilocarpine and epinephrine. Am J Ophthalmol 1971; 72:70-73.
9. Katz IM, Berger ET. Effects of iris pigmentation on response of ocular pressure to timolol. Surv Ophthalmol 1979; 23:395-398.
10. Welsh NH. Failure of filtration operations in Africans. Br J Ophthalmol 1970; 54:594-598. 1 1. Merritt JC. Filtering procedures in American blacks. Ophthalmol Surg 1980; 11:91-94.
12. Miller RD, Barber JC. Trabeculectomy in black patients. Ophthalmol Surg 1981; 12:46-50.
13. Merritt JC, Crawford WJ, Alexander PC, et al. Effect of marihuana inhalation on the intraocular pressure and blood pressure in open angle glaucoma. Ophthalmology 1979; 86:45.
14. Crawford WJ, Merritt JC. Effect of tetrahydrocannabinol on arterial and intraocular hypertension. Int J Clin Pharmacol Biopharm 1979; 17:191-196.
15. Merritt JC, Crawford WJ, Alexander PC, et al. Effect of marihuana inhalation on intraocular and blood pressure in glaucoma. Ophthalmology 1980; 86:222-228.
16. Merritt JC, Cooke EC, Davis KH. Orthostatic hypotension after A9 tetrahydrocannabinol marihuana inhalation. (In press-Ophthalmic Research).
17. Merritt JC, McKinnon SM, Armstrong JR, et al. Effect of oral A9 tetrahydrocannabinol in heterogenous glaucomas. Ann Ophthalmol 1980; 12:947-950.
18. Crawford WJ, Alexander PC, Merritt JC, et al. Tetrahydrocannabinol effect on elevated blood pressure in humans. Prev Med 1978; 7:54.
19. Merritt JC, Olsen JL, Armstrong JR, et al. Topical A9 tetrahydrocannabinol in hypertensive glaucomas. J Pharm Pharmacol 1981; 33:40-41.
20. Merritt JC, Peiffer RL, McKinnon SM, et al. Effect of topical A9 tetrahydrocannabinol on intraocular pressure in dogs. Glaucoma 1981; 3:13 16.
21. Merritt JC, Perry DD, Russell DM. Topical A9 tetrahydrocannabinol (A9 THC) and aqueous dynamics in glaucoma. J Clin Pharmacol 1981; 21:467S 471S.
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2552967/pdf/jnma00062-0013.pdf
