3) The Eye

• retina contains receptor cells that are senstive to the brigntess and color of light
• optic nerve carries imp;ulses from the retina to the brain
• Sclera forms a tough outer later, with a transparent region at the front called the cornea
• Iris controls the size of pupil and the amount of light reaching the retina
• Cliliary muscles and suspensory ligaments can changed the shape of the lens to focus light onto the retina
• Accomodation is the process of changing the shape of the lens to focus on near or distant objects
• To focus on a near object the: Ciliary muscles contract and the suspensory ligaments relax and lens become thicker and refracts light rays strongly
• To focus on distant objects the: ciliary muscles relax and the suspensory ligaments are pulled tight and lens is pulled thing and only slightly refract light rays
• Two common defects of the eyes occur when rays of light do not focus on the retina : mytopia (short sightedness) and hyperopia (long sightedness)
• Generally these defects are treated with spectacle lenses which reftact the light rays so that they can focus on the retina
• New technologies include contact lenses, laser sugery to change the shape of the cornea and replacment eye lenses