How to Explain the Corrections of Bifocals

Once a person reaches 50, it is common for him to need bifocals, according to The Ohio State University Medical Center. At that age, most people develop a condition know as presbyopia, which is caused by the hardening of the crystalline lens in the eye. Bifocals are lenses in glasses that allow you to see in the distance and up close. Use these steps to explain the corrections of bifocals.

Instructions

• 1

  Explain that everyone eventually develops presbyopia, an age-related condition caused by hardening of the crystalline lens in the eye. Presbyopia makes it difficult to see up close. Eyeglasses with bifocals correct or improve vision.

• 2

  Go into further detail by explaining that presbyopia is corrected with additional plus power, according to opticianworks.com. Plus power is the magnifying prescription in a bifocal lens that allows you to see better up close.

• 3

  Use the American Optometric Association's (AOA) information on bifocals. The AOA notes that the biggest part of a bifocal lens is usually for seeing in the distance and the bifocal portion is confined to the lower part of the lens. This allows a person to comfortably alternate between seeing in the distance and up close.

• 4

  Demonstrate a bifocal correction by showing a written prescription for bifocals. Prescriptions are written with O.D. for the right eye, O.S. for the left eye and Add Power or Near Vision for the bifocal portion of the prescription. The Add Power is written with a plus sign before the power.

  The least powerful bifocal correction is written as +1.00 and the most powerful is +4.00, according to the Mayo Clinic. Increments increase in +.25 between +1.00 and +4.00