Reading glasses are primarily measured by their strength, which is indicated in a specific unit.
The strength of reading glasses is measured in units called diopters. These units are also used on standard vision prescriptions. Diopters tell you the amount of refractive power present in a lens. Essentially, this number indicates how much the lens bends light to help you see close objects clearly. The higher the number on your prescription or the reading glasses label, the more powerful the glasses are.
Understanding diopters helps you select the correct strength for your needs:
- What Diopters Mean: A diopter is a unit of optical power. A lens with a 1 diopter strength will bring parallel light rays to a focus at 1 meter. Higher diopter numbers mean stronger lenses that bend light more.
- Common Strengths: Reading glasses typically range in strength from +0.25 to +6.00 diopters, often increasing in increments of +0.25.
- Finding Your Strength: Your required diopter strength usually increases with age. You can determine your needed strength through an eye exam or by using a simple reading chart test.
While diopters measure the strength of the lens, reading glasses also have physical measurements like frame width, lens width, bridge width, and temple length, similar to other eyewear. However, when someone asks how reading glasses are "measured," they are most commonly referring to the lens power.
