HUMAN EYE :-
The human eye is work on the refraction of light through a natural convex lens made up of flexible and transparent living materials and we can see various things around us. Our eye is gifted to us by god.
There are following main parts of human eye are : cornea, iris, pupil, ciliary muscle, eye lens, retina, and optic nerve.
1] Cornea :-
The front part of the human eye is cornea. It is made up of a transparent material. The light coming from the object enters the eyes through cornea.
2] Iris :-
Iris is a coloured membrane behind the cornea. The iris controls the amount of light entering the eyes through cornea.
3] Pupil :-
There is a hole on the middle of the iris which is called pupil of the eye. The pupil appears black. The iris adjust the size of the pupil according to the intensity of light.
4] Eye lens :-
Eye lens is a convex lens made up of a transparent and flexible material. The eye lens is just like a jelly. Eye lens can change its shape to focus light on retina.
Ciliary muscle:-
The eye lens is attached to the ciliary muscle. Ciliary muscle change the focal length of eye lens while focussing.
5] Retina :-
The screen on which the image is formed in the eye is called retina. The retina is work as a screen. The retina having a large number of light sensitive cells called rods and cones.
ACCOMMODATION :-
The ability of an eye to focus the distant objects as well as nearby objects by changing the focal length of eye lens is called accommodation.
The range of vision of a normal human eye is from infinity to about 25 cm.
DEFECTS OF VISION AND THEIR CORRRECTION :-
There are mainly three common types of defects of vision :
1] Myopia [ near sightedness or short sightedness]
Myopia is the defect of vision due to which a person can see the nearby objects clearly but cannot see the distant objects.
Causes of myopia :
1] The decrease in the size of eye lens.
2] The increase in the size of eye ball.
Correction of myopia :
Myopia can be corrected by using a concave lens of suitable power.
2] Hypermetropia [ far sightedness or long sightedness ]
Hypermetropia is defect of vision due to which a person can see the distant objects clearly but cannot see the nearby objects.
Causes of hypermetropia :
1] The increase in the size of eye lens.
2] The decrease in the size of eye ball.
Correction of hypermetropia :
Hypermetropia can be corrected by using a convex lens of suitable power.
3] Presbyopia
Presbyopia is the defect of vision due to which an old person cannot see nearby objects as well as distant objects. Presbyopia can be corrected in the same way as hypermetropia by using convex lens.
Cataract
Cataract is the medical condition in which a formation of membrane cover eye lens due to which a person becomes cloudy results in blurred vision is called cataract. Cataract can be corrected by surgery.
WHY DO WE HAVE TWO EYES FOR VISION AND NOT JUST ONE :-
1] Having two eyes gives a wider field of view. With the help of two eyes we ca cover wider field and the field become 180 degree.
2] Having two eyes enables us to judge distance more accurately. There is a distance of few cm between our eyes due to this, when our two eyes see the same objects with different angles and send to the brain. The brain combines both images and judge distance accurately.
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| HUMAN EYE |
There are following main parts of human eye are : cornea, iris, pupil, ciliary muscle, eye lens, retina, and optic nerve.
1] Cornea :-
The front part of the human eye is cornea. It is made up of a transparent material. The light coming from the object enters the eyes through cornea.
2] Iris :-
Iris is a coloured membrane behind the cornea. The iris controls the amount of light entering the eyes through cornea.
3] Pupil :-
There is a hole on the middle of the iris which is called pupil of the eye. The pupil appears black. The iris adjust the size of the pupil according to the intensity of light.
4] Eye lens :-
Eye lens is a convex lens made up of a transparent and flexible material. The eye lens is just like a jelly. Eye lens can change its shape to focus light on retina.
Ciliary muscle:-
The eye lens is attached to the ciliary muscle. Ciliary muscle change the focal length of eye lens while focussing.
5] Retina :-
The screen on which the image is formed in the eye is called retina. The retina is work as a screen. The retina having a large number of light sensitive cells called rods and cones.
ACCOMMODATION :-
The ability of an eye to focus the distant objects as well as nearby objects by changing the focal length of eye lens is called accommodation.
The range of vision of a normal human eye is from infinity to about 25 cm.
DEFECTS OF VISION AND THEIR CORRRECTION :-
There are mainly three common types of defects of vision :
1] Myopia [ near sightedness or short sightedness]
Myopia is the defect of vision due to which a person can see the nearby objects clearly but cannot see the distant objects.
Causes of myopia :
1] The decrease in the size of eye lens.
2] The increase in the size of eye ball.
Correction of myopia :
Myopia can be corrected by using a concave lens of suitable power.
2] Hypermetropia [ far sightedness or long sightedness ]
Hypermetropia is defect of vision due to which a person can see the distant objects clearly but cannot see the nearby objects.
Causes of hypermetropia :
1] The increase in the size of eye lens.
2] The decrease in the size of eye ball.
Correction of hypermetropia :
Hypermetropia can be corrected by using a convex lens of suitable power.
3] Presbyopia
Presbyopia is the defect of vision due to which an old person cannot see nearby objects as well as distant objects. Presbyopia can be corrected in the same way as hypermetropia by using convex lens.
Cataract
Cataract is the medical condition in which a formation of membrane cover eye lens due to which a person becomes cloudy results in blurred vision is called cataract. Cataract can be corrected by surgery.
WHY DO WE HAVE TWO EYES FOR VISION AND NOT JUST ONE :-
1] Having two eyes gives a wider field of view. With the help of two eyes we ca cover wider field and the field become 180 degree.
2] Having two eyes enables us to judge distance more accurately. There is a distance of few cm between our eyes due to this, when our two eyes see the same objects with different angles and send to the brain. The brain combines both images and judge distance accurately.
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