When purchasing readers, what's most important?

Getting the proper diopter strength is most significant. You'll find self-administered eye tests on most websites and in retail stores. Use such a test before buying reading glasses. If you feel you are able to see best through 2 different strengths of lenses, select the lesser strength. For example, if you can see equally well through +1.50 and +1.75 diopter lenses, get the +1.50s. Also, consider how you will use your eyeglasses. If you're outside a lot, polarized, tinted, or UV filtering readers are great for your eye health.