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प्रश्न
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
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उत्तर
| Defect of vision | Cause | Corrective measure |
| Myopia | Lengthening of eye ball from front to back or the lens is too curved. | Using suitable concave lens |
| Hyperopia | Shortening of eye ball from front to back or the lens is too flat. | Using suitable convex lens |
| Astigmatism | Uneven curvature of the cornea | Using suitable cylindrical lenses |
| Presbyopia | Loss of flexibility of lens | Using suitable convex lens |
| Cataract | Lens turning opaque | Surgery or use of convex lens or implantation of plastic lens. |
| Colour blindness | Genetic defect | No control measure |
| Squint | Formation of cross-eye | Surgery and suitable exercise |
संबंधित प्रश्न
the biological/technical terms for the lens of eye losing flexibility resulting in a kind of long-sightedness in middle aged people.
A man can read the number of a distant but clearly but he finds difficulty in reading a book.
From which defect of the eye is he suffering?
The picture given here shows a person wearing 'half-moon' spectacles. What sort of eye-defect do do you think he has? Why are these particular spectacles useful to him?
A short-sighted person has a near point of 15 cm and a far point of 40 cm.
(a) Can he see clearly an object at a distance of:
(i) 5 cm?
(ii) 25 cm?
(iii) 50 cm?
(b) To see clearly an object at infinity, what kind of spectacle lenses does he need?
An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also (ii) for its correction.
State the main functions of the following:
Tears
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:
Draw a labeled diagram to show how the above mentioned defect is rectified using the lens named above.
Give Reason:
Why do we see clearly in the central region of the retina?
Assertion: Myopia is the defect of vision in which a person cannot see distant objects clearly.
Reason: This due to eye-ball being too short.
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 |
