5 The Human EyeLens: ability to refract light and allow the eye to focusCiliary Muscle: changes the shape of the lensIris: coloured part of the eye made of muscle fibres that contract and expand to open and close the pupil.Pupil: the part of the eye that light passes throughOptical Nerve: connects the eye to the brain
6 The Human EyeThe cornea tissue that forms a transparent, curved structure in the front of the eye; refracts light before it enters the eyeThe retina a layer of rod and cone cells that respond to light and initiate nerve impulsesRod cells are very sensitive to light but cannot distinguish between coloursCone cells detect colours
7 Colour BlindnessThere are three types of cone cells: blue, green, and red.The exact physical causes of colour blindness are still being researched but it is believed that colour blindness is usually caused by faulty cones but sometimes by a fault in the pathway from the cone to the brain.
8 Recall from your study of lenses that when an object is moved, the image also moves. In the eye, however, the distance between the retina and the lens is always the same. So how do we still see clear images at different distances?