Some Important Facts About Human Eye

Dear Sa'ians,

Today we are providing the important Short notes on FACTS ABOUT HUMAN EYE with the help of diagram, so that all SA'ians having clearly vision about the frequently ask topic .HUMAN EYE in various exams.

Least distance of distinct vision is 25 cm.

Defects of human eye and the remedies :

Myopia or short sightedness : A person suffering from myopia can see the near objects clearly while far objects are not clear.

Causes :

•Elongation of eye ball along the axis.

•Shortening of focal length of eye lens.

•Over stretching of ciliary muscles beyond the elastic limit. 

Remedy : Diverging lens is used.

Hyperopia or hypermetropia or longsightedness : A person suffering from hypermetropia can see the distant objects clearly but not the near objects.

Causes:

•Shortening of eye ball along the axis.

•Increase in the focal length of eye lens.

•Stiffening of ciliary muscles.

Remedy : A converging lens is used.

Presbyopia : This defect is generally found in elderly person. Due to stiffening of ciliary muscles, eye looses much of its accommodating power. As a result distant as well as nearby objects can not be seen.

Remedy:two separate lens or a bifocal lens is used.

Astigmatism : This defect arises due to difference in the radius of curvature of cornea in the different planes. As a result rays from an object in one plane are brought to focus by eye in another plane. 

Remedy: cylindrical lens is used.

Some Important Points About HUMAN EYE:

dispersion-The phenomenon by which, a ray of light splits into its constituent colours, when passed through a transparent medium, is known as dispersion.

The sun gives out white light. It is the largest source of polychromatic light.

Myopia is caused due to the

1) Shortening of the eyeball

2) Increase in focal length of the eye-lens.

The ability of the eye lens to change its focal length to focus the images of all the objects, distant or nearby on the retina is known as the power of accommodation. 

The eye lens changes its focal length by changing its thickness with the help of its ciliary muscles.

The power of a lens is defined as the reciprocal of its focal length in metres.