How the Eye Works
The eye works much like a camera. The cornea is the clear tissue at the front of the eye. Through the cornea you can see the iris (the coloured part of the eye). The black hole in the centre of the iris is the pupil, which can vary in size to regulate the amount of light entering the eye. The lens is behind the pupil and cannot be seen without a microscope.
The cornea and the lens combine to focus light rays on to the retina at the back of the eye. The retina then transmits the image to the brain where it is “seen”. Learn more on our Eye Anatomy page.
Ideal Sight (Emmetropia)
When you are short-sighted the cornea and the lens are too strong for the size of the eye, causing light rays to focus in FRONT of the retina. The condition permits clear close-up vision, but objects at a distance are blurred. Until now you’ve had to wear concave-shaped glasses or contact lenses to place the image properly on the retina.
In long-sightedness, the cornea and the lens are too weak for the size of the eye, causing light rays to focus behind the retina. In this condition the vision is blurred for near viewing. Until now you’ve had to wear convex-shaped glasses or contact lenses to place the image on the retina.
In astigmatism the cornea has different curvatures, rather like the surface of a rugby ball. This gives a blurred image. Astigmatism can occur by itself, but more usually it is associated with short or long-sightedness.