Aspheric lenses with curvature changes
Unlike spherical lenses, aspheric lenses have different curvatures on their front surface. It is commonly known that spherical lenses have the same curve across the entire surface. The changes in curvature allow aspheric lenses to have flatter curves than conventional lenses, bringing a thinner and slimmer appearance. From another perspective, an aspheric lens has a profile that is rotationally symmetric, but not a portion of a sphere. In addition to appearance improvement, glasses made of aspheric lenses can still reduce or eliminate spherical aberration as well as other optical aberrations.
In conventional lens types, a heavy prescription usually requires thicker lenses to provide enough visual correction. Those current thinner aspheric lenses eliminate worries about thick lenses for people with serious vision problems. These flattery lenses also bring less bulging from the frame. In most cases, an aspheric design is combined with high-index lens materials, resulting in quite slimmer, thinner and slighter lenses. Besides usual high-index materials, regular plastic can also be used to manufacture aspheric lenses.
Although all aspheric lenses offer a slimmer appearance for every prescription, they have different shapes while dealing with different vision problems. Aspheric lenses for myopia correction are thinnest at the center and thickest at the edge, while those for hyperopia correction are thicker in the center and thinner in the edge. Even if certain portions of aspheric lenses are thicker than other parts, they do have brought an overall thickness reduction.
Eliminate visual and eye distortion
With flattery curves, the center of an aspheric lens fits closer to the wearer’s face. These aspheric lenses bring both more natural external world and more natural the wearer’s eyes. Spherical lenses for heavy hyperopia magnify both the wearer’s eyes and the surrounding objects, while those conventional lenses for myopia minify these things. Both of these two opposite visual distortions bring unnatural images. What’s worse, they result in “bug-eyed” or “beady-eyed” appearance. In contrast, aspheric lenses distort the wearer’s eyes less as seen by other people. Typically this can be deemed an improvement on aesthetic appearance. For a large portion of eyewear users, this improvement is quite critical. In particular, patients with a heavy presbyopia or myopia can benefit from these lenses more than usual.
Just like expensive aspheric camera lenses, aspheric eyeglass lenses provide a wider area of clear vision than traditional spherical lenses. Those conventional lenses have a narrower area of clear vision, so that vision distortion may be aroused if you look away from the lens center. This improvement is probably contributed by the comparably flat profile of aspheric lenses. Compared with traditional lenses that are much thicker and bulge out, aspheric lenses are able to provide better visual acuity at the edge.
A higher price
Aspheric lenses are now available both in single vision and multifocal groups. Complex curves on aspheric lenses require more time and skills from the optician in lens measurements and fitting, so that a higher price is reasonable. Remember that aspheric lenses have much more complicated curves across the surface. Their cosmetic and visual benefits deserve a higher price. The frame selection of aspheric lenses is also a little more complex than those frames for spherical lenses.
A possible concern
In addition, anti-reflective coating is nearly necessary for all aspheric lenses, since the closer distance between the lens and the wearer’s eye brings more reflection from the lens’ front and back surfaces. The reason is that aspheric eyeglasses should be positioned closer to the face. With such a distance, visible reflections on the front and back surfaces may occur. This consequential problem can be resolved by applying an anti-reflective coating to the lenses.