Lens used to treat astigmatism: September 2005
Ans. D: Cylindrical lens Corneal astigmatism is created when the cornea is not a perfect sphere. The astigmatic cornea is curved more in one meridian than it is in the other. These meridians are usually 90 degrees apa (regular astigmatism). The lens can have astigmatism also, this is termed lenticular astigmatism. Lenticular astigmatism is evident when there is a significant difference between the astigmatism as measured on the keratometer and refractive astigmatism Astigmatism is corrected optically with a cylindrical lens. A combination of a spherical lens and a cylindrical lens (spherocylindrical lens) is used to correct a spherical error with an astigmatic error.
Concave lens
Spherical lens
Convex lens
Cylindrical lens