In the dark: Body clocks and blindness
24 January 2015 Last updated at 00:35 GMT
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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