Human eye - in detail

Human Eye :-



Human eye forms real image on the retina. The eyebal is nearly spherical chamber and can be rotate inthe socket by means of its six muscles. The outer co called sclerotic consists of fibrous white tissues. Te front part of sclerotic is transparent. A normal eye has power of accommodation which enables objects as far as infinity and as close as 25 to be focussed on retina .

Near point :- 

The shortest distance at which an eye can see clearly is called near point. 

Least point :-

It is the distance at which an eye can see clearly, it is taken as 25Cm for a normal eye. 

Visual angle :-

The angle which an object subtends at our eye is called visual angle. The apparent size of an object as seen by our eye depends upon the visual angle.

Myopia or short sightedness 

It is the defect of the eye when it cannot see far-off objects clearly. 
Myopia occurs due to 
(a)  elongation of the eye ball, or 
(b)  decrease in the focal length of the lens. 
Myopia is corrected by a concave lens. 

Hypermetropia or long sightedness 

It is the defect of the eye when it cannot see near object clearly. This defect can be corrected by using a converging lense of correct focal length. 

Astigmatism 

It is defect of the eye when a straight object looks as curved. It occurs due to asymmetric curvature of eye lens. This defect is corrected by using cylinderical lens. 
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