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Test
your own field of vision
You
can test your own field of vision. Although this is not a substitute
for the optician's examination, it can be a useful indicator.
1. Close
or cover your left eye and stare straight ahead at a point on a wall
with your right eye
2. Hold
your right hand about 30 cm (1 foot) away from your right ear over
your shoulder
3. Gradually
move your hand forwards, whilst at the same time moving (wiggling)
your fingers
4. You
will become aware of the movement at the edge of your vision
5. Repeat
the manoeuvre, bringing your hand up from your waist, then down from
your head and across from your left hand side
6. You
should see farthest out to your right hand side and below (the view
to the left and above will be restricted by your nose and eyebrows)
7. If
you cannot see your moving fingers until you bring them directly in
front of your eyes, you have lost your peripheral vision
8. If
your field of vision is normal, there is one point at which you will
not see your moving fingers - this is your blind spot
Find
your blind spot
You
should now see a spot and a cross on the screen.
Close
your left eye and look at the spot with your right eye.
Gradually
move closer to the screen whilst looking at the spot.
You
will notice that the cross disappears when you get to between 15 cm
and 30 cm (6 and 12 inches) from the screen.
Repeat
by closing your right eye and looking at the cross with your left
eye.
The
spot will disappear from your view at about the same distance as before
Want
to know more about eyes?
Eye diseases
Vision defects described
Optical illusions
Myths about eyes and vision
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Anteria Chamber
The Anteria Chamber is located between the cornea in front and the pupil and iris behind. It contains aqueous humour. |
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Aqueous Humour
Aqueous Humour is a transparent fluid. |
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Choroid
The Choroid is a sheet of tissue which lines the posteria 2 thirds of the sclera. |
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Ciliary Body
The Ciliary Body is a ring of tissue which extends back from the sclera. The muscles of the ciliary body change the shape of the lens for focussing light. |
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The Cornea
The Cornea is part of the Outer Coat of the eye. It is transparent, colourless and covers one sixth of the eye. As it is supplied with very fine nerve fibres, it is exceptionally sensitive to pain.
It is transparent in order to let light in, and from the front is almost circular. Most of the focussing power of the eye is provided by the Cornea, with the lens providing only the 'fine' adjustment. There is no blood supply to the Cornea, with most of the nutrition being supplied by the aqueous humour. |
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Fovea
The Fovea is a depression within the retina which contains the cones (see retina for details of cones) |
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Iris
The Iris is a muscular diaphragm which contracts or relaxes to control the size of the pupil in bright or low light. It is visible as the coloured part of the eye. |
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Lens
The lens provides some of the focussing power of the eye, so that light rays can be focussed on to the retina. |
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Optic Nerve
The Optic Nerve carries electro-chemical messages from the retina, along the visual pathway, to the visual cortex in the brain. |
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Papilla
The Papilla is the small bump at the entrance to the eye where the optic nerve enters and leaves. |
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Posteria Chamber
The Posteria Chamber is the narrow space between the iris and the pupil in front, and the lens behind. It contains aqueous humour. |
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Pupil
The Pupil is a round black hole through which light reaches the retina. In bright light the pupil closes its size and at night or in low light, it enlarges to allow as much light in as possible. |
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Retina
The Retina is light sensitive and lines the inside of the back of the eye. It sees by means of cones (6 million) and rods (100 million). The cones identify colour and are used for direct vision such as reading. The rods are used for peripheral (side) vision, especially in low light. |
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Sclera
The Sclera
is opaque and makes up 5 sixths of the outer layer of the eyeball. It
is visible between the eyelids as the white of the eye.
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Vitreous Humour
Vitreous Humour is a transparent jelly-like structure which is made up of a network of fibres suspended in fluid. It is contained in the Vitreous Cavity, the largest chamber of the eye. |
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