Class 10 Science

Structure of Human Eye

These notes are based on the chapter Human Eye and Colourful World from class 10 science NCERT book and CBSE syllabus.

  • Human eye
  • Power of accomodation

The human eye is a spherical structure which fits in the eye socket in the skull bone. The main parts of human eye are: cornea, pupil, iris, lens and retina.

structure of human eye

Fig: Structure of Human Eye


The transparent part of the eye which covers the front of eye is called cornea. Cornea covers pupil and iris. The function of cornea is to refract or bend light rays entering the eyes.


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.


Iris is made of muscles. These muscles control the size of opening of pupil.


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 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 upto 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.


The flap of skin over eye is called eyelid. Eyelids help in keeping the cornea moist. The eyelid keeps the cornea moist by sweeping the secretions from lachrymous gland (Tear glands) and other glands. When a person is sleeping, the eyelids remain closed for a purpose. Closed eyelids during sleep prevent evaporation of moisture from cornea. Eyelids also protect against injury through the mechanism of reflex blinking.

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