The Eye Structure of the eye Focusing Light

The Eye

Structure of the eye

Focusing Light • Parallell rays of light are focused on the retina • Light rays are refracted as they pass into the eye • The cornea is responsible for most refraction- it acts like a convex lens • Rays pass through the lens where fine adjustments are made

Accommodation • The way in which the eye adjusts the focusing of light so a sharp image forms on the retina • On a distant object, the light rays diverge only slightly, so the lens is curved less • On a close object the light rays diverge a lot, so the lens is made thicker to bend the rays strongly

Lens made thinner as less bend is needed from distant light Lens bulges allowing the light to be bent strongly

The lens is held in position by a ring of suspensory ligaments The ligaments are fixed to the lens and also to a circle of muscle called the ciliary muscle (the muscle that is responsible for changing the shape of the lens When the muscle is relaxed, it makes a wide cicle around the lens. The suspensory ligaments are pulled tight and the lens is stretched out so that it is thin- your eyes are at their most relaxed When the muscle contracts, it gets shorter- the ring of muscle gets smaller, as it moves inwards, there is less tension on the suspensory ligaments and they no longer pull on the lens, making it fatter

Poor Sight A convex lens bends the light rays inwards before they reach the lens A concave lens bends the light rays outwards before they reach the lens Lens does not bend the light enough Lens bends the light too much The rays have not met when they hit the retina The rays meet before they hit the retina