The diﬀerent parts of your eye and what they do
Aqueous means water, and humour means ﬂuid. This watery stuﬀ ﬁlls the front of the eyeball around the lens.
This is a bit of your retina that is not sensitive to light because there are no rods or cones there. It is the spot where the optic nerve is joined on to the retina.
The choroid is the middle layer of the eye between the retina and the sclera. It also contains a pigment that absorbs excess light to prevent blurring of vision.
The ciliary body is the part of the eye that connects the choroid to the iris.
These are a circle of tiny muscles around the lens. They change the shape of the lens by squeezing and relaxing. They squeeze (making the lens fat) to look at nearby objects, and relax (making the lens thinner) for far away objects.
One of the two types of light sensitive cells in the retina. The human retina contains 6-7 million cones; they function best in bright light and are essential for acute vision (receiving a sharp accurate image). The area of the retina called the fovea contains the greatest concentration of cones. It is thought that there are three types of cones, each sensitive to the wavelength of a diﬀerent primary colour - red green or blue. Other colours are seen as combinations of these primary colours.
This is the lining on the inside of your eyelid and the outside of the front of your eye (except for the special skin of the cornea). You can see some tiny blood vessels on the conjunctiva over your eye. If your eyes get sore, these blood vessels get bigger and your eye looks red.
This is the see-through skin that covers the front of your eye. It is clear like glass and it has no blood vessels in it.
A small indentation at the centre of the macula and is described as the area with the greatest concentration of cone cells, the
messages encoded at the centre of the fovea will be interpreted by the brain in the form of a visual image.
The iris controls the amount of light that enters the eye. The iris is the coloured part of your eye. It forms a coloured muscular
diaphragm across the front of your lens.
The lens focuses light onto the retina. It changes shape to make sure that the 'picture' on the retina is as clear as possible.
The yellow spot on the retina at the back of the eye, which surrounds the fovea, the area with the greatest concentration of cone
cells, and is therefore the area of greatest acuity of vision. When the eye is directed at an object, the part of the image that is
focused on the fovea is the image most accurately registered by the brain.
Is the visible portion of the optic nerve also found on the retina of the eye. The optic disk identifies the start of the optic nerve
where messages from cone and rod cells leave the eye via nerve fibres to the optic centre of the brain. This area is also known
as the 'blind spot'.
This nerve is a continuation of the retina, leaving the eye at the optic disk, and it transfers all the visual information it gets to the
brain, via millions of nerve fibres branching from the rods and cones. It's a bit like the cable that carries all the TV pictures from
your aerial to your TV so that you can see the programs.
This is the hole in the coloured iris. It lets light into your eye. It gets very small in bright light, and bigger in dull light.
The retina works much in the same way as film in a camera. It is a light sensitive layer that lines the interior of your eye. It is made
up of light sensitive cells known as rods and cones. The human eye contains about 125 million rods, which are necessary for
seeing in dim light. Cones on the other hand function best in bright light - there are between 6 and 7 million in the eye - they are
essential for receiving a sharp accurate image; cones can also distinguish colours. They turn the picture they receive into an
electrical message for the brain, which in turn translates that image to you.
One of the two types of light-sensitive cells in the retina. There are about 125 million rods, which are necessary for seeing in dim
light. They contain a pigment 'rhodopsin' (or visual purple) which is broken down in the light and regenerated in the dark.
Breakdown of visual purple gives rise to nerve impulses when all the pigment is bleached (i.e. in bright light) and the rods no
longer function; this is when the cones are activated.
This is the tough skin that covers the outside of the eyeball (except for the see-through cornea). A protective coat that we call
the 'white' of the eye.
These are small glands inside your upper eyelid. Their job is to make tears to keep the surface of your eyeball clean and moist,
and help protect your eye from damage. When you blink, your eyelids spread the tears over the surface of the eye. Small things
that are on your eye (like specks of dust) wash into the corner of your eye next to your nose. Sometimes tears flow over your
lower eyelid (when you cry, or you have hay fever), but mostly the tears flow down a tiny tube at the edge of your lower eyelid,
next to your nose. (If you look very carefully you can see a tiny dot that is the beginning of that tube). This tube carries the tears
to the back of your nose (this is why your nose 'runs' when you cry)
This is a thicker jelly-like liquid that fills the larger part of the eyeball and keeps it in shape. (Vitreous means glassy, because the
vitreous humour is very clear, so that light can pass through it).
We told you the eye was amazing.