Eyeglasses correct problems within the eye by refracting light through either a concave or a convex piece of plastic or glass. People may be nearsighted (myopic), which means they have trouble seeing objects that are far away; farsighted (hyperopic), meaning they have trouble seeing objects that are close up; have an astigmatism, which is an irregularly shaped cornea that can cause all objects to look blurry; or any combination of these.

When ordering eyeglasses, a variety of treatments for the lenses are available depending on how you will use your glasses. Scratch resistance helps to keep your lenses usable longer, and UV protection protects eyes against the sun's rays. Anti-reflective coatings can make it easier to drive at night by decreasing the amount of glare from streetlights and other cars' headlights. Lenses can be tinted to function as sunglasses, or can be made from photochromic material that darkens when you walk in the sun.

Eyeglasses are needed to help people see better. If you have prescription glasses, you may need to wear them all the time or only for tasks such as reading, driving and watching movies. Spectacles usually consist of a pair of lenses that correct vision and a frame that holds the lenses together and helps them to sit in front of your eyes.

Eyeglasses can be made with single lenses that correct for distance or up close, or they can be made with multifocal lenses, which correct for distance and reading. These also are called bifocals. Bifocals can have obvious lines or the lines can be blended or made to appear invisible.

Glasses can be made for safety and sports, for sun wear and for specialty jobs. There are special lenses made for people who need to be able to see up close while looking up, such as pharmacists and plumbers, or at a unique distance, such as musicians who need to read sheet music at arm's length. About 30.8 million people purchase new glasses each year and yet few know about their production, history and life cycle.