Understanding The Eye

The Structure of the Eye

The eye is rather like a small camera. The main function of the eye is to produce a focused image of the visual world on the retina at the back of the eye. This is similar to a camera focusing an image onto the film within it.

The Cornea

This is the clear curved window at the front of the eye. It is made of regularly arranged layers of transparent collagen, and through it you can see the coloured iris. The cornea does most of the focusing of light coming into the eye and needs a smooth and healthy tear film to work well. This tear film is essential for clear vision and the health of the eyes. It has a complex composition including natural antibiotics.

The Sclera

This is the white outer wall of the eye. Its job is to provide structure and strength, and to protect the contents of the eye. It is made of the same collagen material as the cornea but the layers are irregularly arranged which is why it is white rather than transparent. Six small muscles are attached to the sclera and these move the eye around.

The Iris

The iris is the coloured part of your eye, and is like the diaphragm in a camera. The round opening within the centre of the iris is the pupil. Tiny muscles within the iris control the size of the pupil. One muscle makes the pupil smaller and another draws it more widely open. Adjusting the size of the pupil controls the amount of light allowed to pass to the back of the eye.

The Lens

The lens of the eye sits immediately behind the pupil. It is like a lens in a camera. It cannot be seen unless special examination instruments are used. This natural lens, which is made almost entirely of protein, is called the "crystalline lens" to distinguish it from the artificial lens that is placed into the eye as part of a cataract operation. The lens of the eye is about the same size and shape as a smartie - but transparent. It helps with the focus of the eye. In youth a small muscle inside the eye is able to change the shape of the lens and thus adjust the focus of the eye. This ability is gradually lost with age and this is one reason why reading glasses are needed from mid 40's onwards.

The Retina

This is the vital light sensitive layer that lines the back of the eye. It is like the film in a camera. In the deepest (outermost) part of the retina are light detecting cells called rods and cones. These cells sense the image focused onto them and this visual information is converted into electrical signals. These signals then pass into the optic nerve at the back of the eye and from there to the brain.

The colour sensitive cones are concentrated in the central part of your retina (called the macula) which you use for detailed vision, such as reading this. The rods are not colour sensitive, and can only detect black and white. They are found throughout the rest of the retina. They are though particularly sensitive to low levels of light and they enable us to adapt our vision to the dark. In fact our eyes can be an incredible one million times more sensitive in the dark!

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