What are the Different Strengths of Reading Glasses?

As people get older their vision begins to weaken. In many cases, the vision of a person at age 50 is a quarter that of a person who is only 20. Of course, the rate of worsening vision, termed “presbyopia,” varies dramatically from individual to individual.

Units of magnification in reading glasses

The units of magnification used in determining reading glass strength are diopters, a unit used to measure the power of a person’s vision. A person with normal vision can see 40 diopters and can adjust 20 diopters nearer or further. It is therefore a measurement of focal length. The greater the diopter length, the more clearly a person can see close objects. This ability to adjust focus, called accommodation, decreases with age and can be dealt with by using reading glasses. Readymade glasses usually start out with a diopter of about 1.50 and progress upward to 2.75. Prescription glasses may go to 3.00 or above.

Prescription lenses versus readymade lenses

Readymade lenses differ from prescription glasses which are custom-made by a certified optician for an individual’s particular flaws in vision and will have a different prescription for each eye if necessary. Prescription glasses are significantly more expensive and require visiting an ophthalmologist or optometrist, whereas readymade glasses in a variety of strengths are available from various pharmacies, department stores and websites.

Presbyopia and reading glass strength

Because the age-related degradation in vision quality is progressive, it will be necessary for a person to increase the strength of their reading glasses on a regular basis. This is usually done by increasing the magnification of the lenses used in increments of a quarter diopter at a time.