Which one of the following lenses should be used to

Solution

Astigmatism is an optical defect in which visionis blurred due tothe inabilityof the optics of the eye to focus a point object into asharpfocusedimageontheretina.Thismaybe due to an irregular or toric curvature of the corneaorlens.Thetwotypesofastigmatismare regular and irregular. Irregular astigmatism is oftencausedbyacornealscarorscatteringinthe crystalline lens, and cannot be corrected by standard spectacle lenses, but can be corrected by contact lenses.