Multifocals let you focus through different prescriptions at different distances through the same lens — hence the name. Bifocals (meaning a lens with two points of focus (one for distance and one for near) are the most commonly prescribed.
Many people need some visual correction in order to read or see things close-up. Often, bifocals are necessary because people enter middle age and develop near vision problems associated with presbyopia. However, other conditions can cause people of any age to need more help seeing properly in the near range.
Bifocal lenses all work in the same way. A small portion of the eyeglass lens is reserved for the near-vision correction and the rest of the lens is usually a distance correction, but sometimes has no correction at all in it.
Proper use of a bifocal lens is to look up and through the distance portion of the lens when focusing on points farther away, and look down, and through the bifocal segment when focusing on reading material or work up to about 18 inches away.
Similar to bifocals, trifocals are lenses with three points of focus — usually for distance, intermediate and near. Trifocals have an added segment above the bifocal for viewing things in the intermediate zone, which is farther than the near zone — about arm's length away.
Progressive lenses are most often preferred over conventional bifocals and trifocals because images seem to "jump" as the eyes move past the sharply defined boundary between the distance and near parts of a bifocal or trifocal lens. With progressive lenses, the transition between lens powers is smooth and seamless, allowing for a change in focus from distance to near and back again more comfortably.
Progressive lenses, sometimes called "no-line bifocals," eliminate the visible lines of traditional bifocals and trifocals. People love them because no one knows whether they're wearing glasses just for fashion — or because their arms have "grown too short" for them to see up close!
Progressive lenses provide a more natural correction of presbyopia than bifocal or trifocal lenses. Instead of providing just two or three lens powers like bifocals or trifocals, progressive lenses are true "multifocal" lenses that provide a seamless progression of many lens powers for all viewing distances.
With progressive lenses, you can look up to see clearly across the room and in the distance. You can also look ahead to view a computer in the intermediate zone and drop your gaze downward to read and do fine work comfortably. For example a motorists who needs to see in the distance to drive, the intermediate to see the gauges on the dashboard, and up close to read a map would greatly benefit from progressive lenses.
It's easy to adapt to today's modern progressive lenses too. A "corridor" of optimum vision runs vertically down each progressive lens. An optician will take careful eye and frame measurements in order to place the corridor in just the right location so the eyes can naturally access the various powers within the lens for comfortable viewing at all distances. With progressive lenses, the transition between lens powers within the lens is smooth and seamless, letting patients change focus from distance to near and back again comfortably.
Anti-reflective coatings (also called AR or anti-glare coatings) improve vision through the lenses by reducing the glare seen. Each AR layer is scientifically calculated to block reflected light. The result is a reduction in glare, annoying reflections and halos around lights. This is a great safety benefit when driving at night.
AR coatings also improve appearance by reducing the glare that others can see on the lenses. The reflections on the lenses themselves are reduced, creating a nicer cosmetic appearance. With an anti-reflective coating, reflections are eliminated and eyeglass lenses look thinner or non-existent making the eyes more visible.
AR coatings are similar to the coatings found on microscopes and camera lenses. Because of the layering of the coatings applied, AR coatings sometimes have a hint of green or purple color, depending on the manufacturer.
Anti-reflective coating benefits virtually everyone who wear eyeglasses. Research shows wearing AR coated lenses improves night driving vision and increases comfort during prolonged computer use (compared with wearing uncoated lenses).
Transitions are photochromic lenses, which mean they are clear (or nearly clear) indoors and darken automatically in response to sunlight outdoors. They also protect your eyes from 100 percent of the sun's harmful ultraviolet radiation. These features make photochromic lenses a great convenience, because they reduce the need to wear prescription sunglasses in most outdoor conditions.
These lenses are available in nearly every lightweight lens material and lens design, including bifocals and progressive lenses. The variable tint in Transitions photochromic lenses is available in gray or brown.
Photochromic lenses also are great for kids, who tend to spend more time outdoors than most adults. Experts say the risk for cataracts and other age-related eye problems are associated with a person's lifetime exposure to the sun's UV rays, so protecting a child's eyes early on could pay dividends when he or she is a mature adult.
Eyeglass wearers want the most attractive, comfortable eyeglasses available so it's no surprise that most of them want their lenses as thin and light as possible.
Most eyeglass wearers are nearsighted. Nearsighted or Minus lenses have edges that are thicker than their centers. The stronger the prescription, the thicker the lens edge. Lens edges are highly visible in today's fashionable frames that have rims thinner than the lens itself and thicker lens edges detract from the appearance of the eyewear. Nearsighted lenses made of high-index materials are thinner and lighter than the same prescription made from conventional plastic. Thinner edges require less lens material, which reduces the overall weight of the lenses making them more comfortable to wear and more cosmetically appealing.
Lightweight lenses are even more of a benefit for Farsighted or Plus Lens prescriptions, which can make plastic lenses very heavy. High-index lenses also have an aspheric design, which makes them flatter and reduces the magnified "bug-eye" look that conventional lenses cause in strong farsighted prescriptions.
AR coating is a perfect companion for high-index lenses. All lens materials block some light from passing through the lens. This light reflects back from the lens surface, causing distractions and reducing the clarity of vision, especially at night. High-index lenses reflect up to 50 percent more light than conventional plastic lenses. However when an AR coating is applied, high-index lenses allow more light to enter the eye, providing sharper vision with less glare — a real advantage for night drivers. Because AR coatings also eliminate lens reflections, they make high-index lenses appear even thinner which goes a long way in improving appearance.
Polycarbonate lenses are a type of High-Index lenses. They are thinner and lighter than regular plastic lenses and offer 100 percent protection from the sun's harmful UV rays and are up to 10 times more impact-resistant than plastic or glass lenses. This combination of lightweight comfort, UV protection and impact resistance makes polycarbonate lenses an excellent choice for higher prescriptions and safety glasses.
Polycarbonate is mandatory in all children's frames because kids tend to be rough at play even when they are not taking part in an organized sport.
Polarized sunglasses have been popular for years with boaters and fishermen who need to reduce reflected glare from the water surrounding them. But now that others have discovered the benefits of polarized lenses interest in these types of sunglasses has soared.
Besides boaters, anyone who would enjoy a clearer view along with elimination of glare would benefit from a polarized lens. Polarized lenses contain a special filter that blocks reflected light, reducing glare. These sunglasses are great for driving because they reduce glare from flat surfaces such as the hood of the car or the road's surface. Simply put, polarized sunglasses cut glare so your eyes are comfortable and you can see better.
Polarized lenses are also available in bifocal sunglasses or progressive lenses, which are great options for bifocal or multifocal wearers who spend time outdoors.