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The sense of sight. How does it work?

Lets us discuss about the important parts of the eye and their functions:



The front part of the eye is covered by transparent spherical membrane called cornea. Light enters the eye through cornea.

The cornea



Just behind the cornea is a dark-coloured diaphragm which has a small circular opening in the middle.

Iris picture 


Pupil is a small circular opening of iris, the pupil is obvious black because no light is reflected from it. The dark center in the middle of the iris. The pupil determines how much light is let in to the eye. It changes sizes to accomodate for the amount of light that is available.

      Pupil picture


The iris regulates the light by adjusting the size of the pupil.

Let us see how iris regulates and controls the amount of light entering the eye:

When the intensity of light is small or if it is a bright source of light, then the iris makes the pupil to contract and as a result the amount of light entering the eye decreases.

When the intensity of light is less or if the light is dim then the iris dilates the pupil so that more light can enter the eye.

  Non-dilated pupil Vs.Dilated pupil


The eye lens is a convex lens made of a transparent jelly -like proteinaceous material. The eye lens is hard at the middle and gradually becomes soft towards the outer edges.

eye lens

The eye lens is held in position by ciliary muscles. The ciliary muscles

Help in changing the curvature and focal length of the eye lens.



the retina

The inner back surface of the eye ball is called retina. It is a semi-transparent membrane which is light sensitive and is equivalent to the screen of a camera.

The light sensitive receptors of the retina are called rods and cones. When light falls on these receptors, they send electrical signals to the brain through the optic nerve.

Optic nerve-brain connection


The space between the retina and the eye lens is filled with another fluid called vitreous humour.

vitreous humor









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