For those who are young or who need only low-magnification nonprescription glasses to read, the lenses in specs that cost less than a few lattes (about $15) will be as effective as those costing as much as a cappuccino machine (more than $125). That said, if the distance between your eyes, known as your pupillary distance (PD), is unusually narrow or wide, budget glasses may not be comfortable, since their magnification is focused in the center of each lens. "You won't damage your eyes by wearing them, but you may get a headache," says James Salz, M.D., a Los Angeles―based spokesperson for the American Academy of Ophthalmology. And as you age, your PD becomes more important. So if you do have an unusual one, you may find that prescription glasses are more effective.