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A Different Kind Of Vision January 1, 2008

Posted by Mrs Weird Scientist in Human Body, Tough Stuff.
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Eye

When most of us think of the term ‘blind,’ we imagine a total loss of sight. Not quite. At least, not in the traditional way we have viewed blindness. A new study led by Russell Foster at the University of Oxford and Steven Lockley of the Brigham and Women’s Hospital in Boston has found that cells at the back of the eyes in blind people can still gauge light levels. These cells then use this information to set the body’s internal clock to daytime or nighttime. The full experiment results can be seen in the journal Current Biology.

Special Cells

A blind person doesn’t have the rods and cones necessary for normal vision. In a healthy, normal eye, rods and cones serve to catch and focus light, thereby creating the crisp images you are able to see each day. Special cells called retinal ganglion cells – located at the back of the eye – help the brain to differentiate between night and day. How do they accomplish this important task? Well, to start, they operate quite differently from rods and cones. Instead of focusing light as rods and cones do, retinal ganglion cells assess the total light available and then transmit this information to the brain. Approximately 3 percent of retinal ganglion cells react to light and release a chemical known as melanopsin. It’s a weird-sounding word but it’s an important pigment that senses light.

Getting Down To Business

So, how did Foster and Lockley test out their ideas about blindness and retinal ganglion cells? To investigate how these special cells influence the body’s ability to register daytime and nighttime, they performed tests on two blind individuals. First, they shone light for 6.5 hours into the eyes of a man who was blind. Then, after using blue light at nighttime, they managed to delay his body clock regulation by 1.2 hours. The result showed that the man’s retinal ganglion cells were able to register the light. But wait, there’s more! They found that the man’s levels of a sleep hormone called melatonin had fallen by 60 percent, which further shows that the man’s body clock was basically tricked into thinking it’s daytime. Foster and Lockley also examined a blind woman and then performed the same tests, which confirmed their findings.

Figuring It All Out

SunsetA really cool aspect of this research is that it helps to explain an interesting phenomenon that has puzzled researchers and health professionals. Blind people who have had their eyes removed for various reasons tend to experience really poor sleep quality and patterns. This contrasts with blind people who still have their eyes and don’t tend to suffer from the same sleeping problems.

You can consider yourself fortunate to have the vision that allows you to appreciate the beauty of sunrises and sunsets. At the same time, don’t forget that the light our sun brings plays an important role in regulating not only your own body’s internal clock, but the internal clock of a blind person as well.

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