PHYSICS

THE HUMAN EYE

• The Human Eye With this presentation, we will tackle about the following: a. Parts of the Human Eye b. Functions of the Parts c. Defects of the Human Eye
• Fundamental Parts of the Human Eye
• Functions of the Parts of the Human Eye The human eye is the sense organ which helps us to see the colorful world around us. The human eye is like a camera. Its lens system forms an image on a light sensitive screen called retina. The eye ball is almost spherical in shape with a diameter of about 2.3cm. Light enters the eye through a transparent membrane called cornea. Behind the cornea is a muscular diaphragm called iris which has an opening called pupil. The pupil controls the amount of light entering the eye. The eye lens helps to focus the image of objects on the retina. The ciliary muscles helps to change the curvature of the lens and to change its focal length.
• The macula allows us to appreciate detail and perform tasks that require central vision such reading. The vitreous humor comprises a large portion of the eyeball. It is a clear gel that occupies the space behind the lens and before the retina at the back of the eye. Because the eye must process visual data, this liquid must be clear enough that light can easily pass through. The optic nerve transmits electrical impulses from the retina to the brain. It connects to the back of the eye near the macula.
• Human Eye Defects Myopia (Near Sightedness) is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects clearly because the image is formed in front of the retina. This may be due to : i) Increase in curvature of the eye lens ii) Increase in the length of the eye ball It can be corrected by using suitable concave lens. Myopic eye Correction using concave lens
• Hypermetropia (Far Sightedness) is a defect of vision in which a person can see distant objects clearly but cannot see nearby objects clearly because the image is formed behind the retina. This may be due to:- i) Decrease in curvature of eye lens ii) Decrease in the length of the eye ball It can be corrected by using a suitable convex lens. Hypermetropic eye Correction using convex lens
• Presbyopia is a defect of vision in old people in which they are not able to see nearby objects clearly due to the increase in the distance of near point. This is due to the weakening of the ciliary muscles and decrease in the flexibility of the eye lens. It can be corrected by using suitable convex lens. Sometimes they are not able to see both nearby and distant objects clearly. It can be corrected by using bifocal lenses consisting of both concave and convex lenses. The upper part is concave for correction of distant vision and the lower part is convex for correction of near vision.
• Astigmatism is a defect in the eye when the light rays do not all come to a single focal point on the retina, instead some focus on the retina and some focus in front of or behind it. This is usually caused by a non-uniform curvature of the cornea. A typical symptom of astigmatism is if you are looking at a pattern of lines placed at various angles and the lines running in one direction appear sharp whilst those in other directions appear blurred. Astigmatism can usually be corrected by using a special spherical cylindrical lens; this is placed in the out-of-focus axis.
• A cataract is a clouding of the lens, which prevents a clear, sharp image being produced. A cataract forms because the lens is sealed in a capsule and as old cells die they get trapped in the capsule, with time this causes a clouding over of the lens. This clouding results in blurred images.
• Age-related Macular Degeneration (ARMD) is a degenerative condition of the macula (the central retina). It is caused by the hardening of the arteries that nourish the retina. This deprives the retinal tissue of the nutrients and oxygen that it needs to function and causes a deterioration in central vision.
• Glaucoma is a disease caused by increased IOP usually resulting from a malfunction in the eye’s drainage system. The eye produces a clear fluid (aqueous humor) that fills the space between the cornea and the iris. This fluid filters out through a complex drainage system. It is the balance between the production and drainage of this fluid that determines the eyes intraocular pressure (IOP). Increased IOP can cause irreversible damage to the optic nerve and retinal fibers and if left untreated can result in a permanent loss of vision.