The Eye

Sclera - The eye's white protective coat, normally seen as the "white of the eye".

Cornea - The transparent, curved surface at the front of the eye.

Iris - The coloured part of the eye - blue, brown, green, grey etc - that can be seen through the cornea.

Pupil - The hole in the middle of the iris. It constricts or dilates controlling the amount of light passing through.

Lens - The transparent disc (with both sides being convex) immediately behind the iris and pupil. The lens flexes to focus on objects near and far.

Aqueous humour - The transparent fluid that circulates behind the cornea and in front of the lens.

Vitreous humour - The material (like transparent jelly) that fills the eyeball between the lens and the retina.

Retina - The light-sensitive layer of millions of nerve cells that line the back of the eyeball. The Cells -  These consist of two main groups, called rods and cones due to their appearance under the microscope.

Rods – These are more numerous, and are spread out over the entire retina with more toward the outer edge. They respond to low levels of light.

Cones – These are far fewer than rods, concentrated around the retina's centre. They respond to colour and details.

Macula - The small centre of the retina, responsible for reading vision.

Retinal pigment epithelium - This is a dark coloured layer of cells at the back of the retina responsible for providing oxygen and other nutrients to the rods and cones.

Choroid - A large network of blood vessels (behind the retina) that transport oxygen and other nutrients to the retinal pigment cells.

Optic disc - A small yellow oval structure in the retina, to which nerve cell connections travel from all the rods and cones.

Optic nerve - The "cord" of nerve cell connections that passes from the eyeball to destinations throughout the brain.

Function of the Eye

When you see an object, the light travels from that object to the cornea, then passes through the aqueous humour, pupil, is focused by the lens and vitreous humour to reach the retina.

At the macula, the light causes chemical reactions in the cones, that causes them to send electrical messages from the eye to the brain. The cones are therefore responsible for you being able to recognise colours and to read.

The rods are essential to see in the dark, and to detect objects to the sides, above and below the object on which you are directly focused. This function prevents you from bumping into obstacles when moving around.

All the retinal cells (rods and cones) are provided with oxygen and other nutrients from the retinal pigment cells (epithelium), which are kept supplied by the rich network of blood vessels in the choroid.

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