Question

The bifocal lenses are required to correct –
A) Cataract
B) Astigmatism
C) Myopia
D) Presbyopia

Answer 1

Hint: We need to understand what is a bifocal lens, the technique it uses so that it can be used as eye correction device and the type of correction it can make to determine the eye defect which is corrected by these lenses which is the required solution.

Complete answer:
The bifocal lenses are those lenses which consist of two different powers in the two regions of a single lens. It helps people to focus the vision in accordance with the object distance. An object that is near, such as when reading, the lower portion of the lens proves helpful and when the object is far the upper portion of the lens helps in focussing.

We can understand from the above explanation that the bifocal lenses are used for correction of eye defects which involve the inability to focus objects in the retina whether far or near. This seems to be like a person affected by both the short sightedness and the long sightedness.
In humans, the eye lens becomes rigid and less flexible or compressible with age. The muscles weaken which result in inability to focus the image formed in the retina. This condition is called presbyopia. It affects most people at old age and therefore, the bifocal lenses are prescribed to correct the vision. It is similar to long sightedness as the observer finds it difficult to focus the nearer objects.

The correct answer is option D.

Note:
The bifocal lenses are replaced by the progressive lenses which are more comfortable to use as the name suggests the progressive lenses have the powers distributed on the lens in a different and increasing pattern unlike the bifocal lenses.