Originally Answered: Thisis my biology homework but its more of a physics question. Please help! urgent!?
1. The cornea, lens aqueaous and vitreous humour are able to refract light. Light exhibits behavior as a wave. Refracting light means changing the wave rate of the light rays. The cornea refracts light rays to the lens aqueaous, by its physical properties of being transparent and liquid. The lens aqueaous further refracts according to the location of the object being viewed. When light goes trhough air and into liquid, its direction is changed - it is refracted. The muscles at the sides of the eye squeeze the lens aqueaous so that light is focused to the retina. The light travels through the clear aqueous solution that is the vitreous humour and is converted to both chemical and electrical energy before being sent through optic nerves from the retina to the brain.
2. The refractive power of the lens' ability to bend rays of light is by altering the shape of the lens. The muscles attached to the eye squeeze the lens according to the object viewed. The lens which is like an oval shaped transparent aqueaous ball has its surface diameters changed by the squeezing. So when the lens is made fatter, greater diameter, the focal length of the lens is increased and images can be received from objects that are far away. When the lens is more relaxed or looking at things close up, the lens is not squeezed so much and is effectively thinner, reducing the focal length of the lens.
3. Astigmatism is due to the cornea and/or lens aqueaous curvatures are not correct and so the lens as described in #2 is not operating correctly and the light will be focused in more than one location causing blurred vision. To correct it, glass or plastic lenses can be used, or laser surgery can re-shape the cornea.
4. Cataracts can be age related, where the cornea and/or lens loses its transparency, due to leakage, etc. Also they are produced by eye injury or physical trauma, illness, , radiation damage. exposure to excessive ultraviolet, micorwave and x-ray exposure (which have very short wavelengths compared to light), infra-red (which has longer wavelength than light) .
5. Two other less common causes of cataracts are drug side-effects and iodine deficiency.
6. Two main ways cataracts are removed are surgically removing the lens or part of the lens and the use of eye drops containing acetyl-carnosine, which slow down the damage tot he lens. An IOL is an intraocular lens, which would be implanted in the eye to substitute for the removed lens. It is flexible made of a soft clear plastic, so that the muscles of the eye can squeeze it and focus the light in a similar way to the removed lens aqueaous.