For many people, different lenses are needed for seeing at different distances. Bifocal lenses allow the wearer to look through two areas of the lens. One area focuses on distant objects, the other is used for reading. A little-known fact is that bifocals were invented by Benjamin Franklin, and his style of bifocals are still available today.
Most of the time the "reading" area is smaller, shaped like a sideways "D", and found in the lower hemisphere of the lens. These bifocals are called lined bifocals or flat-tops. If you are focusing on distant objects, you look through the top half of the lenses. To read a book, magazine, or newspaper, you look through the "reading" area. The Franklin style lenses are less common, and are split horizontally down the middle of each lens. One thing that can be difficult about using bifocals is dealing with the line between the two vision areas. Fortunately, recent technologies have developed a new type of lens, called the no-line, or progressive lens.
Bifocals allow the wearer to read through one area of the lens, and to focus on distant objects through another area of the lens. As the eyes age, though, a stronger prescription is needed to read. As the bifocal power increases, the range of focus with it becomes more shallow, making it difficult to focus on objects at intermediate distances, such as grocery items on a shelf or your speedometer. Thus, trifocals are necessary for a third prescription for intermediate focusing.
Trifocals, also known as lined trifocals, feature three areas of focusing power, each separated from the other by a distinct line. The three windows allow for focusing on distant objects, intermediately distanced objects, and reading. The downside of trifocals is dealing with the lines between the different focusing powers. The advantage of this design is that the intermediate and near sections are wider than those created in progressive lenses.
One of the main problems with bifocal and trifocal (multi-focal) lenses is that the lines separating the various focal ranges are visible to the wearer, and often cause images to "jump."
An improvement in multifocal design is called a progressive lens. Progressives provide a smooth transition from focusing on nearby to focusing on distant objects because they do not have a distinct line which separates the focusing powers. Instead, a gradual change in power allows the wearer to focus on objects at all distances. Distant objects are viewed through the upper portion of the lens, while near objects are viewed through the middle or lower portion of the lens. These are also great for some computer use.
We all have heard the phrase, "Different strokes for different folks." Well, this holds true in terms of selecting glasses. There are different lenses for just about everybody. No matter what your particular need, there's probably a specialty lens designed for you.
For example, a specialty lens that is becoming increasingly useful is designed for computer users. Computer lenses have "windows" designed for viewing your computer screen, documents on your desk, the keyboard, and near objects for reading. The lenses are designed to reduce Computer Vision Syndrome, or CVS, which is characterized by headaches, eye strain, neck and back aches, dry eyes, blurred vision, and double vision.
Another example is called the double D-segment lens, also known as the double flat-top lens. If you look through the center portion of the lens, you can focus on distant objects. But you can also look through a D-shaped segment near the top of the lens to see nearby overhead objects more clearly. This is very useful if you are involved in work where you're looking at nearby objects above your field of vision, as with carpenters and pilots. The D-shaped segment near the bottom of the lens allows for reading.
A specialty lens that is becoming increasingly useful is designed for computer users. Computer lenses have zones designed for viewing your computer screen, documents on your desk, and distant objects. However, they differ from traditional progressive lenses because they allow more room for the computer zone. The lenses are designed to reduce Computer Vision Syndrome, or CVS, which is characterized by headaches, eye strain, neck and back aches, dry eyes, blurred vision, and double vision.
Double D—Segment Lenses
The double D-segment lens is also known as the double flat-top lens. If you look through most of the lens, you can focus on distant objects. But you can also look through a D-shaped segment near the top of the lens to see nearby overhead objects more clearly. This is very useful if you are involved in work where you are looking at nearby objects above your field of vision, as with carpenters and pilots. The D-shaped segment near the bottom of the lens allows for reading. The doctor and your optician know what's available and what would be the best choice for your needs. If you have a favorite hobby or activity, please be sure to let us know so we can ensure you get the best vision at work and play!
Lens Coatings & Treatments
Normal lenses often create glare, reflections, and "ghost images." Now that can be eliminated with an anti-reflective coating.
What we see is a result of light being sensed by our eyes. With normal glasses, much of the light reflects off the lenses. This produces glare. It also reduces the wearer's visual acuity. In other words, the light reflections are a visual and cosmetic problem.
Anti-reflective coatings increase light transmission through the lenses to 99.5 percent. They make it easier to see and easier for others to see you. These coatings are especially useful for those viewing computer screens and driving at night.
If you wear any of the hard resin lenses, including high index, you should consider getting a scratch- resistant coating. Resins and plastics are more susceptible to scratches than glass. Scratches damage the cosmetic look of the lenses, as well as their performance. With a scratch resistant coating, you don't have to worry so much about minor scratches on your lenses. Another advantage of scratch-resistant coatings is that most coatings come with a one-year warranty. They are a great investment to prevent minor scratches. However, it is important to remember that scratch-resistant does not mean scratch-proof. All lenses are susceptible to scratches.
If you've ever felt frustrated at needing prescription glasses and prescription sunglasses to accommodate an outdoor lifestyle, you should consider photochromic lenses. Photochromic lenses darken when exposed to UV rays. The change is caused by photochromic molecules that are found throughout the lens or in a coating on the front of the lens. When the wearer goes outside, the lenses darken or tint. When the wearer goes back inside, the glasses become clear.
There are a variety of photochromic options available, with choices in color and darkness of tint. One consideration with photochromic lenses is that they do not darken fully when driving in a car because the windshield absorbs most of the UV light needed to activate the tint.
Glare from wet roads, light reflecting off other vehicles, and glare from your own windshield can be annoying and dangerous. To eliminate this glare, we offer polarized lenses. Polarized lenses significantly reduce glare, decreasing eye strain and increasing visibility. Polarized lenses are the most effective way to reduce glare.
Most glare comes from horizontal surfaces, so the light is "horizontally polarized." Polarized lenses feature vertically-oriented "polarizers." These polarizers block the horizontally-polarized light. The result is a glare-reduced view of the world. Polarized lenses can make a world of difference for any outdoor enthusiast. Fishermen can eliminate bright reflections from the water and actually see into the water more easily than with any other sunglasses. Golfers can see the green easier, and joggers and bikers can enjoy reduced glare from the road. In addition, drivers can enjoy the safety and comfort that polarized lenses provide while driving.
Polycarbonate & Trivex
Polycarbonate or trivex are a good choice for active lifestyles, moderate prescriptions, or safety glasses. These materials are about 20% thinner and lighter than standard plastic lenses. Also, they provide the most impact resistance of any material available, which means they are less likely to shatter when impacted at high speeds. Finally, these materials are recommended for semi-rimless and rimless frame designs because they do not tend to chip or crack.
High Index Lenses
Years ago, the only materials available for lenses were glass and a hard resin called CR-39. More recently, high index lenses have become available. High index materials are named because they have a higher index of light refraction. Basically, they can do the same job that glass or CR-39 does, but high index lenses are much thinner and lighter. With high index lenses, you can avoid having "soda bottle" lenses.
When speaking about high index lenses, you may hear many unfamiliar numbers and terms. Here are a few things to remember.
- Polycarbonate: The first and still most popular high index plastic is polycarbonate. Polycarbonate was originally developed for fighter jet cockpits and has been used in the space program. It is light, and very resistant to impact. Most sports lenses are made of polycarbonate.
- Mid-Index: High index materials are classified by numbers. The higher the number, the thinner and lighter the lens. The lower numbers are classified as mid-index lenses. Mid-index lenses are those with numbers such as 1.54, 1.56, and 1.57. These lenses are thinner than glass (1.53), and nearly as strong as CR-39 (1.49), or plastic.
- High-Index: High index lenses, such as 1.60, 1.66, 1.67, 1.70, and 1.71, are much thinner than regular glass or plastic. Talk with our trained optician to decide which high index lens is right for you.