While ready-made drugstore reading glasses are quite inexpensive and available without an eye exam, they only offer the same degree of correction in both lenses, and the optical center of the lenses is not customized to each wearer. These off-the-rack readers are essentially two magnifying lenses mounted in an eyeglass frame. They are not a good option for people who need a different correction in each eye or who have astigmatism (irregularity in the curvature of the cornea). Prescription reading glasses, on the other hand, are not only personalized to each wearer, but they also come with the benefit of a comprehensive eye exam, which is important for detecting other age-related conditions and diseases that pose a threat to vision.
P.S. Prescription bifocals, trifocals, and progressive lenses (“no-line bifocals”) combine needed correction for distance viewing with near correction for reading in a single set of lenses.