LOS ANGELES: Scientists have discovered the function of a third type of light sensor in the eye— not vision, but control of the body’s internal clock, opening a new pathway for potential treatments of light-related mood and sleep disorders.

The sensors, found in only 2 per cent of retinal cells, are dedicated to detecting the presence and intensity of light through the use of a light-sensitive molecule called melanopsin, researchers reported this week in the journal PLoS ONE.

They found that mice without the sensor were unable to reset their internal biological clocks. The nocturnal animals woke up half an hour earlier every evening, never properly adjusting to a 24-hour day, researchers reported this week in the journal PLoS ONE.

Scientists have been searching for light level sensors since the 1920s, when it was noted that some blind patients’ pupils dilated in response to bright light, suggesting the existence of a sensor separate from the rod and cone cells responsible for vision.

Project leader Satchin Panda of the Regulatory Biology Laboratory at the Salk Institute in La Jolla, California, said that searches of the recently sequenced mouse and human genomes revealed that both contained an extra light sensor gene.

The researchers pinpointed the new sensor to a small number of retinal cells. They genetically engineered mice with sensor cells sensitive to a particular toxin. When the mice were exposed to the toxin, only the cells containing melanopsin died.

The animals still could see normally and avoided stepping off an artificial cliff. But their ability to discern and respond to light intensity was destroyed.

The results confirm experiments reported in the journal Nature earlier this year by a separate group using a different genetic approach. —Dawn/The LAT-WP News Service(c) Los Angeles Times