Scientists discover new way of seeing

University of Manchester scientists have found that a new type of light sensitive cell in the eye helps the brain measure brightness. This mechanism, which works alongside the rod and cone cells in the eyes, may be particularly important to people with some sorts of blindness.

Professor Rob Lucas and Dr Tim Brown, whose work is oublished in PLoS Biology today, hope their findings will lead to a new understanding of how we perceive the world, and may eventually even lead to technical applications in artificial lighting, visual display unit and television screen design.

Signals from the rod and cone cells in the eyes send information on movement, shape and colour to the brain via neurons that form the optic nerve. The Manchester team has found 2% of these neurons, that produce a light sensitive protein known as melanopsin, play an integral role in measuring the brightness of thr world around us. It was thought that these melanopsin cells sensed (detected) light primarily for subconscious responses to light, such as regulating pupil size. However the team found melanopsin also helped brain regions involved in conscious perception to measure brightness, not only in normally sighted mice but also in those previously considered blind.

Dr Brown, at Manchester’s Faculty of Life Sciences, said: "This reveals a new role for melanopsin in perceiving brightness and suggests that these cells could support vision even in people with advanced retinal degeneration.

"Loss of rods and cones is a common cause of blindness, but people suffering these conditions often retain some light perception. The accepted explanation for such cases has been that they reflect incomplete rod and cone loss. We have shown that in mice with similar conditions light responses can in fact rely on melanopsin."

Professor Lucas added: "Now we are asking to what extent melanopsin could help the normally sighted to see, and what it might contribute to the blind and partially sighted?

"So far, our results suggest that we rely upon melanopsin to perceive the difference in brightness between a foggy day in London and bright summer sunshine in Manchester. We need to know whether it also provides the spatial information we rely on for more complex sorts of vision.

"Our findings could change the way that we think about artificial lighting and may improve the ability of computer displays or televisions to reproduce our perception of the real world. At the moment both of these technologies are designed with just rod and cone cells in mind."

The study, in which Professor Lucas and Dr Brown collaborated with researchers at the Salk Institute in San Diego and University College London’s Institute of Opthalmology, was funded by the Wellcome Trust.