Human Eye
Structure Of Human Eye:
The human eye is a spherical structure which fits in the eye socket in the skull bone. There are following main parts in the human eye.
Pupil:
Pupil is the round
black spot in front of eye. It regulates the amount of light entering the eyes.
Pupil works like aperture of a camera. In case of dim light pupil dilate to
allow more light to enter the eyes. In case of strong light pupil constrict
allowing less light to enter.
Irish:
Irish is made of
muscles. They control the size of opening of pupil.
Lens:
Lens lies just behind
the pupil. Lens becomes thin to increase its focal length. This enables us to
see distant objects clearly. To focus on nearer objects, lens becomes thick to
decrease its focal length. But there is a limit. The minimum distance of clear
vision is 25 cm. Below this distance, we cannot see things clearly.
Retina:
Retina works like a
screen or camera film. Retina is full of light and colour sensitive cells.
These cells, upon receiving image send electrical signals to the brain, which
processes these information to make a mental image of what we see. The
photoreceptor cells in the eye are of two types, viz. rod cells and cone cells.
The rod cells are sensitive to dim light. The cone cells are sensitive to
bright light and colour.
Benefits of two eyes: One eye is having a field of vision of about 150 degrees. Both the eyes enable us to see up to a field of 180 degrees. Moreover, as two different images get juxtaposed in the brain, so we are able to see a three dimensional view of the world.
Power of Accommodation of Human Eye: The human eye can clearly see a nearby object as well as an object on infinity. This ability of the human eye is called the power of accommodation of human eye.
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