Question

why bifocal lenses are used for presbyopia​

Answer 1

• some old people have problems of myopia and Hypermetropia, as the ability converge or diverge the focal length is lost.
• when people have both these defects if vision it is called as presbyopia.
• presbyopia can be cured by having concave lens in the upper side of the spectacles and convex lens in the lower side of the spectacles.