Unlike spherical lenses, aspheric lenses have different curvatures on their front surface. It is commonly known that spherical lenses have the same curve across their entire surface. The changes in curvature allow aspheric lenses to have flatter curves than conventional lenses, bringing thinner and slimmer appearance.
In conventional lens types, a heavy prescription usually requires thick lenses to provide enough visual correction. Those current thinner aspheric lenses eliminate worries about thick lenses for people with serious vision problems. These flatter lenses also bring less bulging from the frame. In most cases, an aspheric design is combined with high-index lens materials, resulting in extremely slimmer, thinner and slighter lenses. Besides usual high-index materials, regular plastics 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.
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 clear vision area, so that vision distortion may be aroused if you look away from the lens center.
With flatter curves, the center of an aspheric lens fit closer to the wearer’s face. These aspheric lenses bring both more natural external world and more natural 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.
Aspheric lenses are now available both in single vision types and multifocal types. 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. Their cosmetic and visual benefits deserve a high price. The frame selection of aspheric lenses is also a little more complex than that of spherical lenses. 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.
Article Source:http://vision.firmoo.com/eyeglasses/aspheric-lenses-with-curvature-changes.html
