CELLS that help pick out day from night have been discovered lurking at the
back of the eye. These special cells use light to help set the body’s internal
clock, even in blind animals.
The cell “doesn’t care about contrast or colours,” says David Berson of Brown
University in Rhode Island. “It’s almost like the light meter in your camera.”
The finding is striking because the dogma for more than a hundred years was that
there are only two kinds of light-sensing cells in the eye: the rods and the
cones. Some suspected a third kind existed to record light…
