Sooner or later, it happens to everyone: the feeling that your arms are not long enough to read small print. The term presbyopia is a vision condition that make focusing on close objects difficult. The Cleveland Clinic notes that most people over the age of 40 start to notice a need for help with reading and require reading glasses and bifocals.
History
Bifocals are attributed to Benjamin Franklin, noted for his practical and useful inventions. Franklin called his glasses his "double spectacles," and he made them by combining two pairs of glasses into one pair that he could wear all the time. His original diagrams and sketches of the invention are kept at the U.S. Library of Congress.
Significance
Eyeglasses are the most common option for correcting vision. According to the Ohio State University Medical Center, lenses work by adding or subtracting focusing power to the eye's cornea and lens. Bifocals are glasses that allow you to see in the distance and up close. The top part of the lens is for distance viewing and the middle and bottom of the lens are for reading and near work. If you don't need glasses to see far away, the top of bifocal glasses are made with just clear lenses, called plano.
Reading glasses have lenses that fill the whole frame. The glasses can be full-sized or smaller, called half-eyes or readers. The entire lens is used to see only up close.
Types
Bifocal lenses are available in reading glasses in several styles. Lined bifocals, also called D-segs or segments, look like a half-moon upside down in the bottom half of the lens. D-segment lenses have different widths, including 25, 28 and 35 mm. The wider segments provide a larger reading area.
Bifocal lenses are also available as no-line, or progressive lenses.This type of bifocal allows you to read at different distances, depending on where you look through the lens. As you look down through the bifocal, the magnification gets stronger.
Material
Reading glasses with a bifocal lens are available in three different types of material: glass, plastic and polycarbonate. Glass lenses weigh the most but provide the most scratch-resistance and best optics. Plastic lenses are lighter and are available with a scratch-resistance coating but do scratch easier than a glass lens. Polycarbonate is the lightest and most impact-resistant material for lenses. The type of lens you choose depends on your prescription and frame. An optician is trained to help you select the best type of material for your specific needs.
Considerations
The American Optometric Association recommends that people in their 40s have a comprehensive eye examination at least every two years to help with reading prescriptions and bifocals as well as check for other eye and health issues.
