Modern prescription eyeglasses have been worn for hundreds of years. Even though surgery and contact lenses are available to correct vision, eyeglasses remain a popular choice. A multitude of frame and lens choices are available. Understanding the different features and benefits of prescription eyeglasses may help when picking out a new pair of glasses.
History
Magnification has been used to enable people see better since ancient Roman times, when glass globes filled with water helped people read and see fine detail. The first eyeglasses with lenses in a frame were believed to be used in the 13th century in Italy. People began wearing frames in the 1600s that resemble modern eyeglasses like the ones we wear today. A hundred years later, Benjamin Franklin is credited with the invention of bifocals, which have two types of lenses combined into one lens for distance and reading.
Function
Eyeglasses are worn to help see into the distance or for reading or both at the same time. A person who is nearsighted, or myopic, wears lenses that are concave in shape. Farsighted, or hyperopic, lenses are convex. A person who requires bifocal lenses, which correct for nearsightedness or farsightedness and also for reading and close work, is said to be presbyopic.
Material
According to the Cleveland Clinic, prescription eyeglass lenses are available in three basic materials: glass, plastic and polycarbonate. Glass lenses are the most scratch-resistant, but they are also the heaviest. Plastic lenses are the most common, are lighter than glass and are made with a scratch-resistant coating but still scratch more easily than glass. Polycarbonate lenses are a plastic hybrid material that is considered the safest style of lenses and are lighter and thinner than plastic or glass.
Features
A person's lifestyle and prescription should be considered when choosing lens material. Active people and children do best with shatter-resistant polycarbonate lenses. Photochromic lenses that change from light to dark are a good choice for someone who goes from indoors to outdoors frequently. Hi-index or aspheric lenses provide clearer optics and vision for stronger prescription lenses that are extremely thick at the edge or in the center of the lens.
Potential
People who are very nearsighted or farsighted used to be limited in lens choices. However, advances in lens and frame technology have opened up many new possibilities for a variety of vision constraints.
Progressive, also called no-line or invisible, bifocals were previously only available in large frames and limited lens choices. Today progressive lenses come in small or large frames and in many lens styles.
Starting in the fall of 2010, lenses will be available with a new electronic technology that allows the wearer to turn a bifocal on and off inside the lens, giving a much bigger viewing area.
Frames
Prescription eyeglass frames are available in metal or plastic. Metal is durable and usually lasts longer but in general is more expensive. Plastic frames come in a wide selection of colors and styles, but over time plastic may become brittle and break or crack.
