Inner retina may hold key to light response

Two animal studies published in Science show that mice lacking certain retinal photopigment cells have abnormal pupillary responses. These findings may help researchers understand how mammalian eyes respond to light.

One study, conducted at the Washington University School of Medicine in St. Louis, examined vitamin-B-based pigments called cryptochromes in mice. Mice without rods and cones needed 10 times more light to make their pupils constrict compared with normal mice. Mice without rods and cones and without cryptochromes need 100 times more light to achieve pupil constriction. This suggests that these cryptochromes play a role in the brain’s perception of and response to light.

A second study by researchers at Baltimore’s Johns Hopkins University found mice without melanopsin (another potential photopigment) also had abnormal pupil responses.

While not definitive, the studies demonstrate that cryptochromes are key photopigments used by retinal ganglion cells, according to the studies’ authors.