The lids, Blinking & Tears

The cornea has tissue similar to the skin we have on the rest of our body, but because it possesses the special property of transparency it needs plenty of protection. This is where the lids help.

Lids - not just blinking nuisances

• They sweep debris, that has floated into the eye, off the centre and out of harms way. The tearfilm then drains into puncta - tiny holes at the edge of each lid near the nose, one at the top lid and one at the bottom. 'Used tears' finally flow through the puncta into the back of the nose.
  
• Each blink places a fresh layer of tears across the eye. The tear-film has an anti-microbial effect. As they come into contact with the tears harmful airborne 'bugs' are killed before they can damage the eye.
  
• The cornea is unique in that it has no blood supply within it - it gets some oxygen from surrounding tissues. Most of its supply comes from oxygen dissolved in the tearfilm. So each blink carries a fresh supply, helping the cornea survive and remain transparent.
  
• Each blink 'rewets' the front of the eye, restoring a perfect optical 'polish' - necessary to allow us to focus sharply.
  
• Someone throws a stone... Seeing the danger approaching, our lids can close within 1/5 of a second, protecting against injury.
  
• Even the lashes have their part to play, whisking the air and trapping particles that could enter the eye.
  
• The lids protect our eyes during sleep - our eyes actually roll up a little during sleep to ensure that the cornea is totally protected when we are at our most vulnerable.