The eye

Greg Foot demonstrates how the eye works and what happens if someone is long or short sighted

The eye is a sense organ containing receptors sensitive to light intensity and colour.

A labelled diagram of the eye
StructureFunction
CorneaRefracts light - bends it as it enters the eye
IrisControls how much light enters the pupil
LensFurther refracts light to focus it onto the retina
RetinaContains the light receptors
Optic nerveCarries impulses between the eye and the brain
Ciliary muscle/bodyAlters the shape of the lens so that the eye can focus
Suspensory ligamentAttaches the ciliary muscle to the lens

The retina

Light passes through the eyeball to the retina. There are two main types of light receptors - rods and cones. Rods are more sensitive to light than cones so they are useful for seeing in dim light. There are three different types of cone cells which produce colour vision.

The human retina
A photograph of a human retina seen through the eye

The pupil reflex

The amount of light entering the eye is controlled by a reflex action. The size of the pupil changes in response to bright or dim light. This is controlled by the muscles of the iris.

When there is little light the pupil of the eye expands to let in more light