4Functions Eye Lids: Cover and protect the eye by closing. Regular blinking distributes fluid over the eye.Prevent the eye from drying.Pupil:Determines the amount of light entering the eye.Sclera:Tough non elastic fibrous coat round the eye ball.Iris:Contracts or dilates to alter the pupil’s size.
6Functions Cornea: Causes light to refract at the surface of the eye. Lens:It’s a converging lens.Curvature is controlled by ciliary muscles andsuspensory ligaments.Causes light to undergo further refraction.Conjunctiva:Transparent membrane.Covers the sclera and lines the insides of theeyelids.
7Choroid:Layer rich in blood vessels.Supply the eye tissues with oxygen and nutrients.Retina:Projection screen at the back where the imagesare focused.Once focused, vision is good.Optical nerve:Carries the signal from the retina to the brain.Cause of the blind spot in eyes.
8Vitreous:Transparent gel.Fills the main cavity of the eye.Macula:A depression in the retinacones (photoreceptor cells) are concentratedand vision is most acute.
10Process of sight When you look at an object, The light rays are bent, refracted and focused bythe cornea, lens, and vitreous.The lens makes the rays come to a sharp focus onthe retina.The resulting image on the retina is inverted,diminished and real.The light rays are converted to electrical impulseswhich are then transmitted through the optic nerve,to the brain, where the image is translated andperceived in an upright position!
11Short sightedness This person can’t see Causes: far things clearly because light rays meetin front of the retina.Causes:eye ball is too long.eye lens is too strong.cornea is too thick.
12Correction of Short sightedness The person should put on glasses withconcave (diverging) lenses so as to focusfar objects.
13Long Sightedness This person can’t see near things clearly because light rays meetbehind of the retinaCauses:eye ball is too short.eye lens is too weak.cornea is too thin.
14Correction of Long sightedness The person should put on glasses withconvex (converging) lenses so as to focusnear objects.