The Differences In Bifocals, Trifocals, And Progressive Lenses
By Essilor News
Having a hard time reading the restaurant menu? Newspaper print looking a little small? As we age, most people develop something known as presbyopia which makes it harder to see objects that are close to us. Corrective lenses are the best way to combat the effects of presbyopia. But how do you know which type of lenses is right for you?
Bifocal lenses have been around since the late 18th century and were created when Benjamin Franklin cut two lenses in half (each with different corrective powers) and glued them together. Modern day bifocal lenses are still made up of two parts. The top of the lens is made for seeing things at a distance, while the bottom part of the lens is made for viewing things close up, making focusing on books or menus much simpler. The two sections of the lens are usually separated by a visible line. The segment of the lens devoted to correcting near-vision can be in several shapes including a half-moon, a round segment, a narrow rectangular area, or the full bottom half of the bifocal lens.
With only two zones of vision, bifocal lenses do not account for the intermediate zone of vision. Since this intermediate viewing area is about 18 - 24 inches from the face, it can be difficult to view things like a computer screen while wearing bifocal lenses.
In an effort to correct the problem of lacking an intermediate viewing area, trifocal lenses were invented. Trifocal lenses offer correction for near and far vision, but also enable a person to see clearly at an intermediate level (about the length of your arm). Trifocals help correct the intermediate zone by featuring a second small lens segment directly above the area used to correct near vision. This results in a total of three power zones, thus the name trifocal. This intermediate segment allows the wearer to better see things like the computer or the car instrument panel on the dashboard. Just like bifocal lenses, trifocal lenses also contain visible lines on the lenses.
Without any visible lines on the lens, progressive lenses offer a smooth transition from distance through intermediate vision to near vision. Progressive lenses also offer vision correction for all of the in-between vision zones. So instead of just having two or three different viewing zones, progressive lenses offer vision correction that progresses in power from the bottom to the top of the lens. This progression of correction eases eye strain by providing the most natural vision correction. Some people also call these no-line glasses or no-line bifocals.
Modern technology has continued to improve the design of progressive lenses. Some progressive lenses on the market today, like Varilux lenses, are now designed to account for the difference in prescription for both the right and left eyes. These lenses also help cut down on blurry peripheral vision, which can be apparent in other progressive lenses and cause motion sickness.
If you think you are experiencing presbyopia or any other vision problems, talk to your eye doctor about which lenses are right for you. You have a choice!