Reports on the affects of cannabis on vision aren't new. One was written 25 years ago, while another was published more than a decade ago. While these showed how cannabis seemed to improve vision at night, none of the studies were able to explain the physiology behind the effect — apart from identifying that more CB1 protein receptors were located in the eye than the brain for the psychoactive ingredients in cannabis to bind to.
This is what researchers from the Montreal Neurological Institute in Canada sought to understand. In a study published in the journal eLife, the team led by Lois Miraucourt tested the effects of a synthetic form of a cannabinoid on the eye tissues of African clawed toad (Xenopus laevis) tadpoles. They used microelectrodes to measure how certain eye cells responded to light.
The cannabinoid caused the cells to respond more rapidly to bright and dim light. This increase in sensitivity was due to cannabinoid binding with the CB1 receptor and also inhibiting NKCC1 — a protein that brought chloride ions in and out of cells to improve their electrical potential.
"Overall, these experiments show that cannabinoids reduce the concentration of chloride ions inside the retinal ganglion cells, making them more excitable and more sensitive to light," Mo Costandi reports, writing for The Guardian.
What about in humans?
Tests showed how tadpoles exposed to cannabinoids were better at seeing in dark areas. The researchers also noted how both treated and non-treated tadpoles behaved the same way under normal light conditions. In other words, cannabinoid treatment improved the tadpoles' night vision and didn't have side-effects to regular vision.
If the same responses can be monitored in human beings, cannabis presents viable treatment options for retinal diseases, such as retinitis pigmentosa and glaucoma. While we do know that cannabinoids have a neuroprotective effect on retinal cells, several factors still need to be determined, such as, how long do the vision-enhancing effects last. It will also be interesting to see if the vision benefits can be separated from the intoxicating effects of the drug. The number of practical uses for people with night vision likely drops when those people are, well, stoned.
Like many of the supposed effects of cannabis, this one requires further study.