the eye

• sclera - tough, supporting wall of the eye
• Cornea - transparent outer layer at the front of the eye, refracting light onto the eye
• Iris - contains muscles that control the diameter of the pupil and therefore how much light enters the eye
• Lens - focuses light onto the retina
• Retina - contains receptor cells sensitive to light intensity and colour
• Ciliary muscles- controls shape of lens
• suspensory ligaments- control shape of lens
• optic nerve- carries impulses from receptors on the retina to the brain
• when the light receptors detect a bright light, a reflex is triggered that makes the pupil smaller, the circular iris muscles contract and the radial muscles contract
• in dull light radial muscles contract and circular muscles relax
• for near objects, ciliary muscles contract, slackening the suspensory ligaments and the lens becomes fat
• for objects far away ciliary muscles relax, allowing suspensory liagments to pull tight making the lens go thin
• short sightedness is called myopia
• long sightedness is called hyperopia