Describe the function of each part of the eye, limited to: (a) cornea – refracts light (b) iris – controls how much light enters the pupil (c) lens – focuses light onto the retina (d) ciliary muscles and suspensory ligaments – control the shape of the lens (e) retina – contains light receptors, some sensitive to light of different colours (f) fovea – contains the greatest density of light receptors (g) optic nerve – carries impulses to the brain