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Eye, eyesight
 Eye, eyesight – Many problems can occur with our eyesight. Some are shown here.
Muscles to move the eyeball
Problem: About three times the light level is needed to read when you are old than when you are young. Remedy: Make sure reading lights are very bright – use new fluorescent bulbs to keep the cost of good lighting low.
Problem: The eye muscles are weak, and they cannot make the lens change shape enough to see things that are close up.
Remedy: Make signs big enough to be read at more than 60cm.
These muscles stretch the lens to focus.
These fibres connect the muscles to the lens.
Lens
Iris
Cornea
Conjunctiva protects surface of cornea.
The image is focused on the retina.
Rods and cones identify light and colour.
Blind spot
Problem: The lens and fluids in the eye become slightly more yellow. This means that blue and green are hard to see, and dark colours can all seem to be black.
Remedy: Make sure important signs are in red.
Optic nerve
Problem: The lens becomes thicker and scatters the light, so direct lights appear to glare.
Remedy: Do not use harsh direct lights such as unshielded fluorescent tubes.
colour. Brown eyes have a thick iris with lots of coloured cells; blue and grey eyes have a thin iris with less coloured cells.
The pupil changes size to allow just enough light into the retina. Too much light can damage the
sensitive cells in the retina. That is the reason we must never look at very bright light sources, such as the Sun.
The human eye is designed to see through air. That is why it is so difficult to see under water. Water
and the tissues of the eye are very similar, so the eye does not bend the light as much in water as in air. That is why you need a face mask to see properly under water.
Blood vessels of the eye
Fluids of the eye
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