In the simplest of terms, neuroscientists are generally in agreement that the primary cause of cannabis red eye is nothing more than a drop in blood pressure. With cannabis causing blood pressure within the body to drop, this results in dilation of blood vessels as a means by which to enhance blood flow. And when this happens, the blood vessels in the eyes also dilate to improve blood flow, which is why the eyes become redder in appearance.
It is the way in which marijuana is known to have a direct effect on intraocular pressure which has made it one of the world’s most important treatment methods for glaucoma. Patients with glaucoma run the risk of facing permanent damage to their eyes or even going entirely blind due to a buildup of pressure which can over time wreak irreparable damage. When glaucoma patients smoke marijuana on a regular basis, it immediately and effectively reduces pressure within the eye without any of the side effects associated with standard pharmaceuticals and treatment options.
So it’s basically the same in both instances – cannabis reduces blood pressure, enhances blood flow and in doing so has the potential to cause reddening of the eyes. And given the fact that millions of people all over the world are every day relying on a wide variety of drugs to keep their blood pressure under control, it is quite remarkable the research into this particular medicinal property of cannabis remains painfully remedial.