MCQ
Q.
Lenses are widely used in spectacle to
Correct Answer: D
The correct answer is to Correct the eye defects.
- Lenses are widely used in spectacle to correct eye defects.
- There are three common defects of vision that can be corrected with the help of suitable spherical lenses (convex lenses or concave lenses).
- Myopia is also known as Short-sightedness or nearsightedness.
- Due to this defect, the person cannot see the distant objects clearly but he/she can see the nearby objects clearly.
- The far point of the eye having myopia is less than infinity.
- The defect is caused due to the high converging power of eye-lens or due to the eyeball being too long.
- It can be corrected by making use of spectacles containing concave lenses.
- Hypermetropia is also known as Long-sightedness or farsightedness.
- Due to this defect, the person cannot see the nearby objects clearly but he/she can see the distant objects clearly.
- The near point of a hypermetropic eye is more than 25 centimetres away.
- The defect is caused due to the low converging power of eye-lens or due to the eye-ball being too short.
- It can be corrected by making use of spectacles containing convex lenses.
- Presbyopia is a vision disease caused mostly in old age.
- The ciliary muscles become weak and the eye-lens become rigid and the eye loses its power of accommodation in old age in this vision defect.
- In Presbyopia the person cannot see the nearby objects clearly due to loss of power of accommodation of the eye.
- The near point of the old person having presbyopia gradually reduces and becomes much more than 25 centimetres away.
- It can be corrected by making use of spectacles containing convex lenses.
- A person suffering from both Myopia and Hypermetropia uses spectacles having bifocal lenses in which the upper part consists of a concave lens to correct myopia and the lower part consists of a convex lens to correct hypermetropia.
