the eye

• the sclera is the tough white supporting outer layer of the eye
• the cornea is the transparent layer of the eye found at the front of the eye, that refracts light to focus it on the retina
• the iris is the coloured part of the eye that contains muscles to control the size of the pupil and therefore how much light enters the eye
• the lens is a transparent structure that changes shape to focus light onto the retina
• the suspensory ligaments and the ciliary muscles are responsible for controlling the shape of the lens
• the optic nerve is the nerve that carries impulses from the retina to the brain
• the pupil is the hole through which light enters the eye
• the retina is the light-sensitive layer at the back of the eye containing 2 types of light receptor cells : rods which are sensitive to light intensity and cones which are sensitive to colour
• to see distant objects the ciliary muscles relax causing the suspensory ligaments to tighten making the lens pull thin and less curved so the light doesn't bend as much so light is focused on the retina.
• The eye focuses light onto the retina by changing the shape of the lens this is known as accommodation
• to look at near objects the ciliary muscles contract which slackens the suspensory ligaments causing the lens to go fat and more curved, which bends the light more
• The iris changes shape to adjust to the light. When rods detect bright light a reflex makes the pupil smaller. So radial muscles relax and the circular muscles contract. This reduces amount of light that can enter the eye so that the retina is not damaged. When the rods detect dim lighting radial muscles contract and circular muscles relax causing the pupil to widen letting in as much light as possible