Lids - not just blinking nuisances
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.
Blinking and Tears have various functions:
- 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.
© Terence Mendoza 2001-2006.This information is for
personal information only and may not be reproduced by any commercial
company without prior written consent of the author. Teachers
and students may freely utilise this information for study purposes.
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