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प्रश्न
What is presbyopia? Write two causes of this defect. Name the type of lens which can be used to correct presbyopia.
उत्तर
Presbyopia is a defect of the eye because of which a person cannot see nearby objects clearly. This defect occurs because of the loss of the power of accommodation of the eye. Presbyopia usually occurs in old age.
The two causes of this defect are as follows.
1. Weakening of the ciliary muscles in old age.
2. Reduction in the flexibility of the eye lens.
Presbyopia, which is a special kind of hypermetropia, can be corrected by using spectacles with convex lenses.
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संबंधित प्रश्न
Match the following:
| Column I | Column II |
| (i) Myopia | (a) Converging power of eye lens becomes low |
| (ii) Hypermetropia | (b) Converging power of eye lens remains the same |
| (c) Converging power of eye lens becomes high |
The optical prescription for a pair of spectacles is :
Right eye : −3.50 D
Left eye : −4.00 D
Which is the weaker 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 spectacle lenses will converge light rays or diverge light rays.
Describe and explain, how a normal eye can see objects lying at various distances clearly.
A man driving a car can read a distant road sign clearly but finds difficulty in reading the odometer on the dashboard of the car. Which of the following statement is correct about this man?
(a) The near point of his eyes has receded away.
(b) The near point of his eyes has come closer to him.
(c) The far point of his eyes has receded away.
(d) The far point of his eyes has come closer to him.
Given below is certain structure. Write against them its functional acivity.
retina and ……………………….
In what two ways is the yellow spot different from the blind spot?
Draw a labeled diagram of the front view of human eye.
When light rays enter the eye, most of the refraction occurs at the ____________.
The pigmented circular area seen in front of the eye:
