Picture of the eyes
Our eyes are vital for seeing the world around us, but vision can be impaired by a number of medical conditions, as well as by the ageing process.
The eye is a slightly asymmetrical globe, about one inch (2.5 cm) in diameter.
The front part of the eye - the part you see in the mirror - includes:
- The iris - the pigmented part
- The cornea - a clear dome over the iris
- The pupil - the black circular opening in the iris, which lets light in
- The sclera - the white part
- The conjunctiva - an invisible, clear layer of tissue covering the front of the eye, except the cornea
Just behind the iris and pupil lies the lens, which helps to focus light on the back of the eye. Most of the eye is filled with a clear gel, called the vitreous. Light projects through the pupil and the lens to the back of the eye. The inside lining of the eye is covered by special light-sensing cells, together called the retina. The retina converts light into electrical impulses. Behind the eye, the optic nerve carries these impulses to the brain. The macula is a small sensitive area within the retina that gives central vision. It is located in the centre of the retina and contains the fovea.
Eye colour is created by the amount and type of pigment in the iris. Multiple genes inherited from each parent determine a person’s eye colour.
The amazing human eye: Your guide to how the eye sees
Travel inside the eyes, our window to the world, and learn how they allow us to see objects both far and near.
In order to see, there must be light. Light reflects from an object and, if one is looking at the object, enters the eye.
The first thing light touches when entering the eye is a thin veil of tears that coats the front of the eye. Behind this lubricating moisture is the front of the eye, called the cornea. This clear covering helps to focus the light.
On the other side of the cornea is more moisture. This clear, watery fluid is the aqueous humour. It circulates throughout the front part of the eye and keeps a constant pressure within the eye.
After light passes through the aqueous humour, it passes through the iris. This is the coloured part of the eye. Depending on how much light there is, the iris may contract or dilate, limiting or increasing the amount of light that gets deeper into the eye. After light travels through the iris it enters the pupil - the black dot in the middle of the eye. The light then goes through the lens. Just like the lens of a camera, the lens of the eye focuses the light. The lens changes shape to focus light that has been reflected from near or distant objects.