CANNABIS CAN AFFECT VISION SAY SCIENTISTS

A FAMILY of chemicals that includes the "psychoactive" ingredients of
marijuana plays a role in vision, scientists have found. The discovery
sheds new light on claims by Caribbean fishermen that a rum-cannabis punch
helps them see in the dark.

For the first time, "receptor" proteins activated by this family of
compounds - cannabinoids - have been reported in the eye, providing a
missing link in efforts to understand the retina. The work also provides
greater understanding of the effects on vision of marijuana and hashish,
suggesting that reports of the perception of a "snowy" visual field,
increased light intensity and altered vision may be due to effects in the
retina, rather than the brain. It may even explain why Jamaican fishermen
claim that a punch made of cannabis mixed with rum aids night vision.

"The scientific literature on marijuana, the known effect of cannabinoids
in other parts of the brain and the places we find the receptor in the
retina all make plausible the notion that cannabinoids may well have an
effect on light sensitivity or light-dark adaptation," said Alex Straiker,
of the University of California, San Diego.

However, the retina is "incredibly complex", so this remains only a
possibility, said Mr Straiker, principal author of the report on the
prevalence of receptors - docking points for cannabinoids - in the retina.
The paper appears today in the Proceedings of the National Academy of
Sciences.