Aspheric Lenses for Better Vision and Appearance

In 1990, a new type of lens called "aspheric" was introduced. It rapidly became one of the most popular and useful lens categories. Conventional lenses have a front surface that is spherical, shaped much like the surface of a ball. But aspheric lenses have a more complex front surface that gradually changes curve from the center of the lens all the way out to the edge.

In plus (farsighted) lenses, the front surface gradually flattens toward the edge of the lens. In minus (nearsighted) lenses, the surface gradually steepens toward the lens edge. This gradually changing surface provides a number of important benefits, most important of which is that vision through an aspheric lens is usually superior to vision through a conventional lens.

A basic principle of optics dictates that a slight distortion is created when wearers look away from the center of a conventional lens, whether the gaze is directed to the left or right, above or below. Aspheric lens designs reduce or eliminate such distortions. This is because, as the eye travels away from the center of the lens, the front curve changes, keeping the optics crisp and clear. This is why all expensive camera lenses feature aspheric curves.

Another benefit of aspheric lenses is much like that provided by high-index lenses (see the article on high-index lenses). In a completely different manner than high index, aspheric lenses also end up thinner than conventional lenses, even when made in conventional plastic.

In the case of aspheric lenses, however, this cosmetic thinning is produced by the design of the lens, not by a higher index material. Even so, many of the newer aspheric lenses are made of high-index materials, providing the maximum in both thinness and improved vision.

In an aspheric design, the lenses have flatter curves. This means lenses do not "bulge" out of the frame as much as regular lenses. The side profile of aspheric lenses is thinner, which greatly enhances the appearance of finished eyewear. While high-index lenses primarily benefit people who are nearsighted, aspherics provide substantial benefits for both nearsighted and farsighted wearers.

Also, the flatter aspheric lenses end up positioned closer to the face. This is a major benefit for anyone wearing a strong correction.

For strong farsightedness, aspheric lenses reduce magnification of the eye. The eye at left is seen through an aspheric lens. Through a conventional lens, the eye at right appears larger, even though the lens is the same power.

Strong farsighted lenses have a tendency to enlarge the wearer's eyes, producing an unattractive magnified look. Strong nearsighted lenses do just the opposite: they minify the wearer's eyes so they tend to look small and beady. Positioning a strong correction closer to the eyes lessens this magnification or minification, for a more attractive, natural look.

In minus lenses for nearsighted people, the front surface curves steepen away from the center and toward the lens edge. As a result of this gradual curve change, lenses end up with thinner edges. From an appearance standpoint, the thinnest possible edges for a strong nearsighted lens are produced when the aspheric lens is made of a high-index material.

An even newer type of aspheric lens for strong nearsightedness has aspheric curves on the back side of the lens. This produces the thinnest possible edges for very strong minus prescriptions.

Most popular lens designs can now be ordered in aspheric form, including bifocals, progressive addition lenses (no-line bifocals) and single vision. Some are made from high-index materials, too.

Plus aspheric curves flatten toward the edge. (Curves are exaggerated for graphic purposes.) Drawing: Vision Consultants, Inc.

For several reasons, frame selection is important with aspheric lenses. In general, the best looking eyewear results when the frame is not overly large and when the eyes are centered in the middle of the frame opening. Your eye doctor or optician will guide you in selecting the best type of frame to use with your new aspheric lenses.

Taking measurements for aspheric lenses requires greater care and skill on the part of the optician, but this only requires an extra minute or two. Creating the complicated curves used in aspheric lenses makes them a little more expensive than conventional lenses. But the outstanding cosmetic and visual benefits of these marvelous lenses make them a good investment.

Since aspheric lenses are flatter and positioned slightly closer to the face than conventional lenses, some wearers may notice more reflections off the flatter back surface of the lenses. The best way to eliminate these reflections is to order an anti-reflective coating, which also improves vision through the lenses.