How Progressive Lenses Work

The baby-boomer generation is maturing, but "mature" doesn't have to mean "old" anymore. If you're a 40-something who having trouble reading the fine print, you have more options than just the lined bifocals your parents wore.

Progressive-addition lenses (PALs), sometimes referred to as "no-line bifocals," not only provide visual correction for distances that traditional bifocals can't, but they also hide the fact that you even need reading glasses. No one else has to know whether you're sporting a pair of glasses just for fashion — or because your arms have "grown too short" to allow you to see up close.

Progressive lenses are the closest to how natural vision is (before the onset of presbyopia) that you can get in a pair of eyeglasses. They are more than just a defined near and distance correction in one lens. Rather, progressives provide a smooth transition from distance through intermediate to near, with all the in-between corrections included as well. This constant graduation of the prescription means that you can look up to see in the distance, look ahead to view things such as the computer in the intermediate zone, and drop your gaze downward to read and do fine work comfortably close up.

One example of how distance, intermediate, and near vision fields are mapped out in progressive lenses. This particular design is the Percepta Lens by SOLA.

You get the best vision through the lens when looking directly at the object of focus. There is a "corridor" of optimum vision that runs vertically down each lens. Your eyecare practitioner will measure both eyes in relation to the position of the frame in order to place the corridor in just the right location for you. So you'll get the best vision when you point your nose directly at whatever you want to see.

A great number of curves are present in the lens in order to achieve the progression from one area of focus to the next. These curves are graduated vertically in the center and brought out to the sides of the lenses to be "blended" together. Although most of that blended area is eliminated when the lenses are cut down to fit the eyeglass frame, the side areas that remain do not provide the best vision.

While progressive lenses typically are worn by older people, a recent study suggests that they may also be able to slow progression of myopia in children whose parents also are nearsighted.

Until recently, another disadvantage of the progressive corridor was that an eyeglass frame had to be a rather large size in order to accommodate all of the areas of focus in the lens. If the frame was too small, the reading portion would wind up being cut off, defeating the purpose of a progressive lens. Nowadays, lens manufacturers have overcome that difficulty by offering progressives that are more compact to fit into the small frames that are so fashionable.

Many different progressive lenses are on the market today. The differences among the lenses are mainly in the width of the central corridor of optimum vision. Different areas of the corridor are expanded depending on the function that each particular lens is designed for. Some progressives that are made for a great deal of computer use, for example, have a wider intermediate zone. Others have a larger reading portion. Your eyecare practitioner is in the best position to evaluate which lens style will work best for you.

Choose a frame that's big enough to include all viewing zones. Some progressive designs are compact, to fit in the smaller frames now in style.

The lenses also come in many different materials, including glass, plastic, high-index and polycarbonate as well as photochromic glass, plastic and high-index.

There is a short adaptation period when you are fitted with your first pair of progressive lenses, which can range from a few minutes to a few days. People with certain types of corrections, including strong plus (also called "strong farsighted"), prescriptions tend to have more difficulty adapting to progressive lenses.

Manufacturers are aware that not everyone will be comfortable wearing progressives, so most offer a trial period of a few weeks. During this time, you can exchange the progressives for a lined bifocal or single-vision reading glasses if you are not able to wear the progressives successfully. Manufacturer policies vary, and the eyecare professional who fits the progressive lenses can discuss the available options with you.