- 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.
- The Human Eye
- The Human Eye Refractive index of lens different for each wavelength (colour) Cool colours (blues) appear closer; warm colours (reds) further away Agree?
- Most people see the red, Closer than the blue. Others see the opposite. How about you?
- The Human Eye Your eyes are about to get a workout. Have you stretched your eye muscles yet? No? Then do that now!
- Are you seeing spots?
- Look at the cross for 10 seconds. What do you see?
- Are these lines bent….?
- …or straight?
- What shapes do you see?
- Reading What is wrong with with this sentence? Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
- Do you see the rabbit or the duck?
- Read This Out Loud.
- Are You Sure? Read again.
- The Human Eye
- Structure & Function IRIS coloured part of eye controls light entering PUPIL black hole in iris where light enters
- Structure & Function SCLERA whites of the eye supports eyeball provides attachment for muscles LENS converging lens allows us to see objects near and far
- Structure & Function CORNEA transparent bulge over pupil focuses light (refracts) onto retina RETINA internal membrane contain light-receptive cells (rods & cones) converts light to electrical signal
- Blind Spot On retina where optic nerve leads back into the brain No rod or cone cells Other eye compensates for this area Try this test to prove you have a blind spot…
- Close left eye and approach screen while staring at the letters…watch the dot!
- Structure & Function OPTIC NERVE Transmits electrical impulses from retina to the brain Creates blind spot Brain takes inverted image and flips it so we can see
- Structure & Function RODS 120 million cells detect brightness (black & white) for night vision CONES 6 million cells detect colour (RGB) GANGLION CELLS Detect movement and patterns
- Normal Eye Focus “Blind spot”
- Video YouTube “The Human Eye” and “How the Human Eye Works”
- Focusing Problems HYPEROPIA Far-sightedness Problem seeing close objects Distance between lens and retina too small Light focused behind retina Corrected with converging lenses
- Far-Sighted (Hyperopia)
- Focusing Problems PRESBYOPIA Form of far-sightedness Harder for people to read as they age Lens loses elasticity Corrected by glasses with converging lenses
- Focusing Problems MYOPIA Near-sightedness Problem seeing objects far away Distance between lens and retina too large Light focused in front of retina Correct with diverging lenses
- Near-Sighted (Myopia)
- Diseases of the Eye ASTIGMATISM Eye cannot focus an object’s image on a single point on retina Cornea is oval instead of spherical Causes blurred vision Some types can be corrected with lenses
- Diseases of the Eye GLAUCOMA Group of diseases Affects optic nerve - pressure Loss of ganglion cells Gradual loss of sight and eventual blindness Check eyes regularly Can be treated
- Diseases of the Eye CATARACTS Clouding forms in lens due to denaturing of lens protein Obstructs passage of light Caused by age, chronic exposure to UV, or due to trauma Removed by surgery
- Vision Correction CONTACT LENSES Artificial lens placed over cornea Same as glasses Corrects for both near and far-sightedness Also used for cosmetic purposes (eye colour, Hollywood)
- Vision Correction LASIK “Laser Assisted In Situ Keratomileusis” Refractive surgery using laser Corrects near and far- sightedness and astigmatisms
The details or information above are from a powerpoint presentation. Please click the link below to see these powerpoint presentations the reporters in our class showed us during their discussion about this topic:
Blogger's note: The slideshows don't belong to me nor to the reporters (as they told me they downloaded it in the internet). So I give the credits to the rightful owners.
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Blogger's note: Pictures and slideshows are not mine. Credits to the rightful owner.
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