As people age, the lenses in their eyes thicken and the muscles controlling their eyes weaken. Many people find it difficult to read because their eyes do not properly focus on nearby objects. This condition, known as presbyopia, starts around age 35 to 40 for nearly everyone. The simple solution to this common problem is a pair of reading glasses.

What reading glasses do

Reading glasses correct the effect of presbyopia by magnifying an image and making it easier to read.

Diopter strength

Reading glasses are rated according to their "diopter strength" which increments in 0.25 units. Weak reading glasses typically start at 1.00 and increase in increments of .25 to 3.00 or more.

Magnification

Subtracting 1 from the diopter strength gives you the percentage by which the glasses magnify an image. For example, a strength of 1.25 increases magnification by 25% (1.25 -- 1 = .25). A strength of 4.00 increases magnification by 300% (4 --1 = 3).

Stress glasses

During stressful times, you may need a second pair of reading glasses with higher strength for your presbyopia.

Second pair

As you age, you become more presbyopic, which may require higher-strength reading glasses as often as every year.

Presbyopia vs Myopia

Prebyopia focuses the image behind the retina and is fixed with self-prescribed glasses. Myopia (nearsightedness) focuses the image in front of the retina and requires prescription glasses to correct.