The eye works much like a camera. The cornea
is the clear tissue at the front of
the eye. Through the cornea you can
see the iris (the coloured part of the eye). The black
hole in the centre of the iris is the
pupil, which can vary in size to regulate
the amount of light entering the eye. The lens
is behind the pupil and cannot be seen
without a microscope. The cornea and
the lens combine to focus light rays on to the retina
at the back of the eye. The retina
then transmits the image to the brain
where it is “seen”.
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Short-sightedness
(Myopia)
When you are short-sighted
the cornea and the lens are too
strong
for the size of the eye, causing
light rays to focus in FRONT
of the retina. The condition
permits clear close-up vision,
but objects at a distance are
blurred. Until now you’ve
had to wear concave-shaped glasses
or contact lenses to place the
image properly on the retina. |
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Long-sightedness
(Hyperopia)
In long-sightedness,
the cornea and the lens are too
weak for
the size of the eye, causing
light rays to focus behind the
retina. In this condition the
vision is blurred for near viewing.
Until now you’ve had to
wear convex-shaped glasses or
contact lenses to place the image
on the retina.
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Astigmatism
In
astigmatism the cornea has different
curvatures, rather
like the surface of a rugby ball.
This gives a blurred image. astigmatism
can occur by itself, but more
usually it is associated with
short or long-sightedness.
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