Progressive Lenses

By December 15, 2014 Eye Glasses No Comments

Progressive LensesIf you’re in your forties or older and your eye doctor has prescribed bifocals, don’t despair.

Presbyopia — the normal loss of ability to focus clearly on near objects that comes with age — affects everyone eventually. But these days, you don’t have to wear conventional bifocals with visible lines across the lenses that broadcast your age.

Progressive lenses — also called progressive addition lenses (PALs) or “no-line bifocals” — are multifocal lenses that have the distance portion of your eyeglasses prescription in the top half of the lenses and gradually incorporate the added magnification (near “add”) for reading in the bottom half of the lenses.

The best part: progressives have no annoying bifocal line.

The first progressive eyeglass lenses were introduced in 1959. Since then, continual improvements in progressive lens design and technology have made PALs more and more popular. Today, progressive lenses are more popular than bifocals and trifocals combined.

Advantages of Progressive Lenses

Besides providing a more youthful appearance, line-free progressive lenses usually produce a more complete and natural-feeling correction of presbyopia than bifocals or trifocals.

Instead of having just two (“bi-focal”) or three (“tri-focal”) lens powers, progressive lenses have a seamless progression of lens powers for all viewing distances.

With conventional bifocals and trifocals, images appear to “jump” as your eyes move past the sharply defined boundary between the distance and near parts of the lens. With progressive lenses, the transition between lens powers is gradual and seamless, letting you change focus from distance to near and back again more comfortably, with no abrupt changes in magnification.

When wearing properly fitted progressive lenses, you can see clearly across the room and farther away without any head movement. By lowering your gaze just a few degrees, you are now looking through the intermediate zone of the lenses so you can clearly see objects that are approximately arm’s length away (such as a computer screen). Drop your gaze a bit further and you are looking through the near zone of the lenses for reading and other close-up tasks.

To make sure this “corridor” of gradually changing lens powers in the central portion of progressive lenses is properly positioned for the best wearing comfort, your optician will take careful measurements of your eyes and the eyeglass frames you choose.

Limitations of Progressive Lenses

No multifocal lenses can reverse the effects of presbyopia or perfectly mimic your eyes’ ability to quickly and comfortably change focus when viewing objects at all distances and directions.

Even the most advanced progressive lenses have some minor limitations and may take some getting used to when you wear them for the first time.

Limitations of progressive lenses include:
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Reduced intermediate and near fields of view.

Most modern progressive lenses produce a very wide, clear field of view for distance vision, which is essential for tasks such as driving.

But in order for a multifocal lens to contain lens powers for multiple viewing distances without visible lines and abrupt power changes, the lateral visual field of the intermediate and near portions of progressive lenses is smaller — smaller, in fact, than the field of view for these distances that standard bifocals and trifocals provide.

Generally, the lateral field of view of the reading portion of progressive lenses is about half that of the distance portion of the lens, and the intermediate field of view is narrower still.

In other words, the overall visual field provided by progressive lenses has roughly an hourglass shape — with the top half of the hourglass (distance zone of the lens) significantly wider than the bottom half (reading zone) and the narrowest portion in the middle (intermediate zone).

Sensation of movement.

The slightly reduced clarity of peripheral vision through the bottom half of progressive lenses can give some wearers a sensation of movement (or “swim”) when they turn their head.

This potential problem has been reduced significantly with new progressive lens designs and fabrication technology. In particular, “digitally surfaced” or “freeform” progressive designs typically are less likely to produce this sensation.

Frame size limitations.

Because progressive lenses change in power from the top to the bottom of the lens, the eyeglass frames you choose must be large enough vertically to accommodate the lens design. If the frame is too small, it’s possible some of the reading zone will be eliminated when the lenses are cut to fit into the frame.

This potential problem, too, has been reduced by new progressive lens technology. New lens designs have been developed to accommodate smaller frame sizes. In these “short corridor” progressives, there is a faster transition from distance to reading power in the lens.

Not ideal for prolonged computer use.

Since the intermediate viewing zone of general-purpose progressive lenses has a relatively narrow field of view, most progressives are not ideal for prolonged computer use (though they are acceptable for short-term viewing of a computer screen or other objects at arm’s length).

If you have presbyopia and work at a computer for hours at a time, ask your eye doctor or optician about single vision or multifocal “computer glasses” that provide a wider, more comfortable viewing zone for prolonged computer use.

Adapting To Progressive Lenses

When you are fitted with your first pair of progressive lenses (or a new progressive lens design), there may be a short adaptation period before the lenses feel perfectly comfortable. This might take only a few minutes, or it could take a few days.

As you are adapting to progressive lenses, be aware that your satisfaction often will improve significantly as you learn to make very minor adjustments to your head position (both laterally and vertically) to insure your eyes are in the center of the best viewing zone of the lens for your visual needs.

Most people adapt very easily to wearing progressive lenses. In fact, wearer satisfaction for most progressive lens designs is well over 90 percent.

But if you continue to have problems wearing progressive lenses comfortably after a week or two, see your eye care professional for troubleshooting.

Article ©2013, Access Media Group LLC. Source: Progressive Lenses Replace Bifocal for Age-Defying Appearance by AllAboutVision.com.

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