In the dark: Body clocks and blindness
Our eyes are the window through which we make sense of the colours, people and objects around us.
But scientists at Oxford University say they have another important role - setting our internal body clocks.
When bright light enters the eye in the morning, it kick-starts the brain into generating a regular pattern of sleeping and waking.
So what does that mean for people who can't see anything at all?
Smitha Mundasad reports from Oxford.
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24 Jan 2015