学英语-眼睛 The Eye.ppt

EYE The eye is an extension of the brain Eye brain proxomity Can you see : the optic nerve bundle? Spinal cord? Cross section You must know the position of: Retina Lens Cornea Sclerotic Optic nerve Cilary muscles Suspensory ligaments Retina – receives the image Full of light receptors which are sensitive to: Colour Light levels Massive blood supply is also needed Fovea is the main focal point and has greatest density of light receptors Retina receptors Light receptors are called rods and cone Focusing on objects The lens and cornea focus the light on the retina Focusing The lens job is to make the rays hit the same point The red rays will be out of focus Bending light Light is refracted and bent to focus it as it passes through the lens Lens thickness can be changed so the amount of bending is changed Near vision to bend the light more to focus it Fat lens needed Distance vision Rays enter the eye closer together Need less bending Thinner lens needed Changing lens thickness The lens is slightly elastic, its relaxed state is short and fat. Cilary muscles are attached to the lens, when contracted they pull the lens thin Controlling light levels Your eye are very sensitive and can be damaged by harsh light. Your iris controls light allowed into the eye by changing the size of the pupil * * * * * * * * * * * * * * * * * * * * * * * *