Astigmatism Question

Q1.

An eye test shows that a person suffers from astigmatism.

(i)     Give the main cause of astigmatism.
(ii)    State the effect of astigmatism on the image seen.
(iii)   State the type of lens needed to correct this defect of vision.
(iv)   Give two quantities which must be known in order to manufacture the correcting lens.

 (Total 5 marks)