The front of the eye, and the cornea in particular, has more nerve endings per millimetre square than anywhere else in the body, says Dr Dilani Siriwardena, a consultant NHS ophthalmologist at Moorfields eye hospital in London and vice-president of the Royal College of Ophthalmologists. So it can be very sensitive. The tiniest scratch or piece of grit in your eye can feel like a brick.
If we told them to look at the face, they could usually manage it. But they were mostly looking at the hands. The Prakash children eventually learn to look at faces when spoken to - usually a few months after their surgeries. Their experiences reveal that seeing doesn't come naturally the moment a person is cured of blindness. Newly-sighted people must learn to see.
Blindness is a very scary disability, says Prof Lauren Ayton, deputy director of the Centre for Eye Research Australia at the University of Melbourne. But people don't realise actually about 90% of vision loss can be prevented or treated. And like many other problems, keeping the eyes healthy so often comes down to good diet, keeping active, and regular check-ups.