Concept:Bifocal lenses combine two prescriptions in a single lens to handle vision at different distances.
Explanation:Presbyopia is the age-related loss of the eye's ability to focus on close objects.
It occurs because the crystalline lens hardens and loses elasticity with age.
A bifocal lens has two distinct zones: the upper zone is for distant vision, and the lower zone is for near vision.
In effect, it serves as both a distance lens and a reading lens at once.
The other defects require different corrections: myopia is corrected by a concave lens, hypermetropia by a convex lens, and astigmatism by a cylindrical lens.
Only presbyopia requires two different focal powers in one lens.
Hence, the bifocal lens is the appropriate correction for presbyopia.
Answer:D. presbyopia.