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What You Need To Know

When deciding about the lenses for your new eyewear there are many considerations which you have to evaluate. Eyeglass lenses are defined by a variety of characteristics. The first is dictated by your visual needs, you may require single vision lenses, bifocals or multifocals. Within each of these categories you will need to evaluate the lens form. In addition, the lens material needs to be assessed. The environment in which you wear your glasses dictates several characteristics. And, you can consider how thin and lightweight you would like your new eyewear to be by considering the index of refraction, the Abbe value and the specific gravity. Finally, you should evaluate how you want your lenses to appear, by evaluating the many lens treatments.

When you look at something more than twenty feet away, we call this optical infinity. At that point you eyes are relaxed and parallel. As you begin to focus at objects closer than twenty feet your eyes converge and drop down and the internal lens within you eye begins to add magnification for close viewing, in a process known as accommodation. Technically the distance between 20 feet and two feet is your intermediate range. And, from that two foot distance and closer, within your arm’s length, your are using your near vision. Generally, under the age of 40 your eye has sufficient power to focus comfortably right up to 16 inches, which is the distance at which you hold a good book when reading. With time you will start to hold your reading material further away until one day your arms just won’t be long enough!

Single Vision

Single vision lenses are technically deigned to allow you to see clearly at a distance, more than twenty feet away. Under the age of forty the average eye still has enough amplitude of accommodation to allow your eye to comfortably focus through that correction and to read or see the computer.


In the old days, when you started to have trouble reading up close, you might have worn a bifocal. As the name indicates that lens design provides two distinct points of clear focus. One is long distance, you have to see well when you drive. The other is near. As your eyes come together and drop down to read they cross a clear line of demarcation and pass into a near segment where you would experience an abrupt increase in magnification. This would allow you to read at some fixed distance. Besides the annoying line, bifocals don’t work well in today’s visually demanding world.


Today we need to see near and far and every distance in between. We need to drive, see an office presentation, focus comfortably at the computer, view the keyboard and read. All these activities are performed at different distances. Each requires a slight different amount of magnification. Modern line free progressive power lenses are the answer.

Line free lenses provide a smooth transition between the distance and the near zones allowing the wearer to immediately focus on anything from very far away to very close, all with no distracting line.

The Professional Opticians at Parrelli Optical® are qualified to design and dispense the lastest in lens designs to enhance your comfort and improve your vision.