The human eye and the colorful world long 2

Question 1

Explain the process of accommodation ?

Answer 1

The change in the curvature of the eye lens can change its focal length. When the muscles are relaxed, the lens becomes thin. Thus, its focal length increases. This enables us to see distant objects clearly. When you are looking at objects closer to the eye, the ciliary muscles contract. This increases the curvature of the eye lens. The eye lens then becomes thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.

Question 2

What are the main three common refractive defects of vision ?

Answer 2

(i) Myopia or near -sightedness.
(ii) Hypermetropia or far -sightedness.
(iii) Presbyopia.

These defects can be corrected by the use of suitable spherical lenses

Question 3

What is Myopia ?

Answer 3

A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. Such a person may see clearly upto a distance of a few meters. In a myopic eye, the image of a distant object is formed in front of the retina and not at the retina itself. This defect may arise due to

(i) excessive curvature of the eye lens,
(ii) elongation of the eyeball.

This defect can be corrected by using a
concave lens of suitable power.