Question

name the three common defects of vision what are their causes name the type of lenses used to correct each of them

Answer 1

1) Myopia (near sightedness) :Concave lens of suitable focal length are used to correct it.

2) Hypermetropia(far sightedness) :Convex lenses of suitable focal length are used to correct it.

3) Presbyopia:Both concave and convex lenses are used to correct it.

Answer 2

Answer:

(i) Myopia:  

Cause: Elongation of the eyeball.

Type of lens used for correction: Concave lens of suitable power.  

(ii) Hypermetropia:

Cause: Shrinking of the eyeball.

Type of lens used for correction: Convex lens of suitable power.  

(iii) Presbyopia:  

Cause: Weakening of ciliary muscles.

Type of lens used for correction: Bifocal lens.