Rightly or wrongly, the eye is often held up as the crowning achievement of evolution (or indeed as something beyond evolutionary explanation. Wrongly).

School biology always seems to cover the “rods and cones” cells that detect light on the retina. But another class of cells has now been found to have a direct role in detecting light.

Russell Foster remembers his first human subject, an 87-year-old woman, as she sat in a dark room facing a backlit pane of frosted glass. A genetic disorder had destroyed the light-sensing rod and cone cells in her eyes, leaving her blind for the past 50 years. She was convinced that she would see nothing. But as the wavelength of light in the room shifted to blue, she reported — after some hesitation — a sort of brightness.

“That just blew us away,” says Foster, a neuroscientist at the University of Oxford, UK, and one of the senior authors of a 2007 study reporting the finding[Zaidi, F. H. et al. Curr. Biol. 17, 2122-2128 (2007)].

Foster and his collaborators had done nothing to treat the woman’s blindness. Instead, her awareness of light owed itself to a class of light-sensitive cells discovered in 2002. Studies of these intrinsically photosensitive retinal ganglion cells (ipRGCs) have since revealed many surprises. Scientists initially thought that, rather than contribute to vision, the cells simply synchronized the circadian clock, which sets the body’s 24-hour patterns of metabolism and behaviour, with changing light levels. However, recent work suggests that ipRGCs have been underestimated. They may also have a role in vision — distinguishing patterns or tracking overall brightness levels — and they seem to enable ambient light to influence cognitive processes such as learning and memory.

Full story: http://www.nature.com/news/2011/110119/full/469284a.html