According to research at the University of Aachen a single oral dose of 7.5 mg THC, which was applied to eight healthy medical doctors in a self-experiment, reduced intraocular pressure (IOP) and increased blood circulation in the retina. Measurements were performed before and two hours after intake of THC.

THC resulted in a significant medium reduction of IOP from 13.2 mm Hg to 11.8 mm Hg. The time for the passage of blood from arteries to the veins in the retina decreased significantly from 1.77 seconds on average to 1.57 seconds. Systemic blood pressure and heart rate were not significantly altered. Researchers concluded that "cannabinoids, already known for their ability to reduce IOP, may result in increased retinal hemodynamics. This may be beneficial in ocular circulatory disorders, including glaucoma."

Abstract available at: http://www.cannabis-med.org/studies/study.php

(Source: Plange N, Arend KO, Kaup M, Doehmen B, Adams H, Hendricks S, Cordes A, Huth J, Sponsel WE, Remky A. Dronabinol and retinal hemodynamics in humans. Am J Ophthalmol 2007;143(1):173-4.)