Topic- Human eyeBy- SHREET MISHRA (K.V. OMTINAGAR,

2ND SHIFT, LUCKNOW)

CONCEPTS EXPLAINED-1- HUMAN EYE 2- HUMAN EYE PARTS3- EYE DEFECTS4- POWER OF ACCOMODATION5- CARE OF EYE

HUMAN EYE

RETINAThe retina is the film of the eye. It converts light rays into electrical signals and sends them to the brain through the optic nerve. The sides of the retina are responsible for our peripheral vision. The center area, called the macula, is used for our fine central vision and color vision. The retina is where most the problems leading to vision loss Occur. Three of the leading causes of blindness, from retina damage, are Retinitis Pimentos, Macular Degeneration and Diabetic Retinopathy

IRISThis is the colored part of the eye: brown, green, blue, etc. It is a ring of muscle

fibers located behind the cornea and in front of the lens. It contracts and expands,

opening and closing the pupil, in response to the brightness of surrounding light.

Just as the aperture in a camera protects the film from over exposure, the iris of the

eye helps protect the sensitive retina.

LENSDuring modern cataract surgery the outer membrane of the lens is left in

place. The artificial intraocular lens is placed in this sack

CORNEAThe cornea is a clear, dome-shaped surface that covers the front of the eye. It is

the first and most powerful lens in the eye's optical system. To keep it transparent

the cornea contains no blood vessels. Tears that flow over it and aqueous humor in

the chamber behind it keep it nourished. When you hear of eye banks and eye

transplants, it is the cornea that is being replaced. The cornea can be damaged

from: accidents, infections, and genetic defects.

EYE DEFECTS

1- MYOPIA

2- HYPERMETROPIA

3- CATARACT

4- PRESBYOPIA

HYPERMETROPIA

Hypermetropia, also known as farsightedness or long-sightedness,

is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or the lens cannot become round enough), causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred. Convex lens is used to correct such disease.

Image of Hypermetropia

MYOPIA

Myopia, commonly known as being nearsighted or shortsighted, is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object. Concave lens is used to correct such disease.

Image of Myopia

CATARACT

THE EYE LENS BECOMES OPAQUE.

REMEDY - SURGICAL REMOVAL

Presbyopia

A person who is suffering from nearsightedness or myopia in their earlier age may develop the defect of farsightedness or hypermetropia in their old age due to weakening up of cilliary muscles. Such person is neither able to see distant objects clearly nor able to see nearby objects clearly.

Presbyopia• Cause of Presbyopia

• This defect may arise due to following reasons

• 1. Weakening of cilliary muscles due to age factor.

• 2. Loss of elasticity of eye lens and becoming rigid.

• Cure for Presbyopia

• As in this defect person suffers from farsightedness as well as nearsightedness he is equipped with the spectacles having bifocal lenses. The upper part of the lens is concave in nature to enable him to focus at distant objects and lower part of the lens is convex in nature to enable him to focus at nearby objects.

PresbyopiaAn eye with presbyopia can neither focus clearly at distant objects nor at nearby objects .

A normal eye can focus on distant as well as nearby situated objects clearly

Spectacles With Bifocal Lens

Power of Accommodation

• Power of an eye to form the image of close and far situated objects on the retina by adjusting the focal length of crystalline eye lens with the help of cilliary muscles is known as power of accommodation.

• Light rays coming from the objects situated close to the eye are more diverging as compared to the objects situated far away from it. Hence eye lens has to increase its power in order to converge the more diverging rays and for this cilliary muscles pushes the cartilaginous eye lens from its sides to increase its thickness and thereby increase the power of the lens. But there is a limit of thickening the eye lens by cilliary muscles and increasing its power. Hence there is a limit of the closeness of the objects from the eye up to which an eye can see them clearly and distinctly. The Minimum distance up to which an eye can see clearly is known as least distance of distinct vision.

CARE OF EYE

1- DO NOT SEE VERY BRIGHT SOURCE OF LIGHT

2- DO NOT READ IN VERY DIM LIGHT

3- WASH EYES WITH COLD WATER

4- DO NOT RUB EYES IN CASE ANY THING HAS FALLEN IN.

5- CONSULT EYE DOCTOR IN CASE OF EYE PROBLEM.

THE

END