Human EYEsDon By :

Ali Abdul Hameed Al-Hammadimohammad fahadة

hazza hamadاGrade :12-06

Supervised by: RIYAD ALSHAIKH

Topics that will be coveredGeneral Information about Eye’show does the eye work analogous to a camera.The Camera and the EyeDescribe three vision defects

Nearsightedness Farsightedness and Astigmatism

Explain which kinds of lenses are needed to correct the previous vision defects.

Lenses picture.Correction of Common

Vision Defects

How eyes works?The individual components of the eye work in a manner similar to a camera. Each part playsa vital role in providing clear vision. So think

of the eye as a camera with the cornea, behaving

much like a lens cover. As the eye's main focusing element, the cornea takes widely

divergingrays of light and bends them through the

pupil, the dark, round opening in the center of the

colored iris. The iris and pupil act like the aperture of a camera

The Camera and the Eye

Images are formed in a camera by refraction in a manner similar to image formation in the eye. However, accommodation to image closer objects is done differently in the eye and camera

WHAT IS NEARSIGHTEDNESS ?Nearsightedness, or myopia, is

the inability to see distant objects clearly. (You are "near-sighted," so things up-close are

clear but things far away are blurred.One or more of the following

physical factors causes myopia: 1) the cornea is too steep; 2) the

lens inside the eye is too curved; 3) the eyeball is too long. Whichever factors are

involved, the eye focuses light too quickly — in front of the

retina instead of directly on it

What causes nearsightedness

How is nearsightedness treated

Like astigmatism, myopia can be corrected with prescription

eyeglasses, contact lenses and refractive surgery. Nearsightedness can also be corrected non-surgically with a special type of gas permeable

(GP) contact lens fitting called orthokeratology (or "ortho-k"). In

ortho-k, you wear specially designed GP lenses while you sleep, then

remove them during the day. Ortho-k provides only temporary correction of

myopia, however. The nearsightedness will return if you discontinue wearing the cornea-

reshaping lenses at night.

What is farsightedness ?Farsightedness, or hyperopia, is the inability to see clearly at any

distance without excessive focusing effort. Usually,

farsightedness affects near vision more than distance vision. But in

severe hyperopia, vision is blurred at all distances.

What causes farsightedness?Hyperopia is caused by 1) the cornea

being too flat; 2) the lens inside the eye being too flat; 3) the eyeball being too

short; or a combination of these factors. The result is that the eye focuses light

too slowly — behind the retina instead of directly on it. Farsightedness can be

present in childhood; it can also worsen later in life.

What is astigmatism?Astigmatism is blurred or distorted vision at all distances

What causes astigmatism

Astigmatism typically is caused by an irregularly shaped cornea (the clear front surface of the eye). A

common analogy used to describe astigmatism is that your eye is

shaped more like a football than a baseball. A relatively uncommon

condition called keratoconus can cause severe irregular astigmatism

The End Hop to enjoy it