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प्रश्न
Ciliary muscles of human eye can contract or relax. How does it help in the normal functioning of the eye?
उत्तर
The ciliary muscles of the human eye can contract or relax the eye lens and help in changing the focal length of the eye lens. Because of this, the eyes can focus the images of nearby as well as distant objects on the retina.
We can understand this by following examples:
(a) When the eye is focussing on a distant object. In this case, the ciliary muscles are completely relaxed. The relaxed muscles tightly pull the suspensory ligaments, which in turn pull the eye lens, because of which the eye lens becomes thin. The thin eye lens has a small converging power, which is sufficient to converge the parallel light rays from the distant object to form an image on the retina.
(b) When the eye is focussing on a nearby object. In this case, the ciliary muscles contract, because of which they cannot pull the suspensory ligaments tightly. As the suspensory ligaments are loose, they stop pulling the eye lens, and therefore the eye lens bulges and becomes thick. The thick eye lens has greater converging power, which helps in converging the diverging light rays from the nearby object to form an image on the retina.
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संबंधित प्रश्न
Define the term.
Power of accommodation of the eye.
A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads :
Left eye : +2.50 D
Right eye : +2.00 D
State whether these lenses are thicker in the middle or at the edges.
A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads :
Left eye : +2.50 D
Right eye : +2.00 D
State whether these spectacle lenses will converge light rays or diverge light rays.
List, in order, the parts of the eye through which light passes to reach the retina.
Explain why, we cannot see our seats first when we enter a darkened cinema hall from bright light but gradually they become visible.
Which of the following changes occur when you walk out of bright sunshine into a poorly lit room?
(a) the pupil becomes larger
(b) the lens becomes thicker
(c) the ciliary muscle relaxes
(d) the pupil becomes smaller
In what two ways is the yellow spot different from the blind spot?
With reference to the functioning of the eye, answer the question that follow:
What is the shape of the lens during distant vision?
Match the following:
| Column - I | Column - II |
| 1. Retina | a. Path way of light |
| 2. Pupil | b. Far point comes closer |
| 3. Ciliary muscles | c. near point moves away |
| 4. Myopia | d. Screen of the eye |
| 5. Hypermetropia | e. Power of accommodation |
Arrange and rewrite the term in group in correct order to be in a logical sequence, beginning with the term that is underlined:
Pupil, Aqueous humour, Retina, Vitreous humour.
