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Just how does the eye work? |
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The
eye is a fantastic piece of natural engineering. It copes
with extremes of light and dark, capable of focussing from
inches to infinity, and has a design life of 70-plus years.
The 'nuts & bolts'
Think of the eye as a camera and you cannot
go far wrong. Instead of film at the back of the eye we have
the retina. And just as the lens at the front of the camera
focuses an image on the film, so the eye's own focussing system
of cornea and lens places an image on the retina. Long sight
and short sight are caused by images being brought to focus
behind the retina (longsight) and in front of the retina (short-sight).
Astigmatism is
caused by the eye being shaped like a rugby ball. Both the lens
and the cornea must be clear if good images are to be formed.
On a camera you focus the lens by moving it towards or away
from the film - have a look at your own camera.
The eye is much more sophisticated. Instead, the lens actually
changes shape as muscles around it relax and contract to bring
things into focus. Also, on a camera, the aperture (the small
hole that lets the light through) can be made bigger and smaller
to cope with light and dark situations - and that's precisely
what the pupil in your eye does.
The retina then converts the image you see to electrical signals
for your brain to decode, just like a camcorder's CCD chip.
So you see, the eye is just like a miniature camera - but far
more valuable to you!
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