question_answer 26)

A person looking at a mesh of crossed wires isable to see the vertical wires more distinctly thanthe horizontal wires. What is this defect due to ? How is such a defect of vision corrected ?  

Answer:

This is due to the defect of lenses called astigmatism. The defect arises because ofthe fact that curvature of the eye-lens andthe cornea is not same in different planes. This defect is removed by using cylindricallens with vertical axis.