Ganglion cells help set the human body clock

Cells at the back of the eyes of profoundly blind people monitor light levels and use them to set the body's clock to either day or night, according to a report published in the December issue of Current Biology.

Russell Foster from the Nuffield Laboratory of Ophthalmology, University of Oxford, UK and colleagues from other UK and US centres conducted an experiment on two blind people who lack the rods and cones needed for normal vision.

For 6.5 hours, the researchers shone light into the eyes of a 56-year old blind man and an 87-year old blind woman. When they used the blue light at night-time, they were able to delay the body clock cycle by 1.2 hours, proving that the ganglion cells were registering light. At the same time, blood levels of the sleep hormone melatonin fell by 60% and the patients' alertness sharpened and brain activity increased, demonstrating that the body clocks had been "fooled" into thinking it was daytime.

The researchers believe that the results of this study explain why blind people, who have had their eyes removed for cosmetic or health reasons, can suffer significant sleep disruption.