Chapter 30, Problem 15A

To determine

To explain: Astigmatism and its correction.

Explanation of Solution

Introduction:

Human eyes is the most sensitive part of our body and is most vital organs also as it enables to see the colourful world. However if it is unable to adjust its accommodation, it suffers from some defects too namely: farsightedness, near sightedness and astigmatism.

All of us have a nearly round and spherical eye ball which enables our eye lens to correctly focus upon the subject and refract it while proper bending at our retina to see them clearly. However it may happen that the eye ball of some persons may not be perfectly round and the cornea from where the refraction of light rays occurs in the eyes is curved in one direction more than the other and is flat. This condition does not allow the light rays to properly bend at the edges of eye lens and is unable to form the image clearly at the retina. As a result, there leads a blur or distorted vision of any object and strain on eyes. It can arise due to a prolonged illness in eye, its injury or surgery.

To cure this defect, cylindrical corrective lenses also called toric lenses are prescribed which have a greater curvature in one direction than the other.

Conclusion:

Hence, astigmatism is that defect of eye which arises due to irregular curvature of eye ball and is corrected by using cylindrical lenses.