Isegoria

Decades ago, pharmacologist M. E. West of the University of the West Indies in Kingston, Jamaica, noted that local fisherman who smoked cannabis — or drank cannabis-laced rum — had “an uncanny ability to see in the dark,” which enabled them to navigate their boats through coral reefs:

“It was impossible to believe that anyone could navigate a boat without compass and without light in such treacherous surroundings,” he wrote after accompanying the crew of a fishing boat one dark night, “[but] I was then convinced that the man who had taken the rum extract of cannabis had far better night vision than I had, and that a subjective effect was not responsible.”

Some of these crew members told West that Moroccan fishermen and mountain dwellers experience a similar improvement after smoking hashish, and in 2002, another research team travelled to the Rif mountains in Morocco to investigate further. They gave a synthetic cannabinoid to one volunteer, and hashish to three more, then used a newly developed piece of kit to measure the sensitivity of their night vision before and after. Confirming West’s earlier report, they found that cannabis improved night vision in all three of their test subjects.

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West had suggested that cannabis might improve vision by acting on the eye muscles to dilate the pupils, so that more light falls on the retina, but other experiments ruled this out by showing that marijuana constricts the pupils. It’s also possible that the drug can influence activity in the visual cortex at the back of the brain, but the CB1 receptor protein, which binds the psychoactive ingredient of cannabis, is found at far higher levels in the eye than in the visual cortex, suggesting that any effects the drug has on vision are likely due to its actions on retinal cells.

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