Progressive lenses, also called progressive addition lenses, progressive power lenses, graduated lenses and varifocal lenses, are eyeglass lenses used to correct presbyopia and other disorders of accommodation. A gradient of increasing lens power is added to the correction for the other refraction error, going from a minimum or nothing at the top of the lens to maximum magnification at the bottom of the lens. A wearer can then adjust the lens power required for clear vision at different viewing distances by tilting his or her head to place the line of sight through different parts of the lens.
Progressive addition lenses avoid the discontinuities in the visual field created by bifocal and trifocal lenses. The lenses are also more cosmetically attractive. The lenses suffer the disadvantage of creating regions of distortion and blur away from the optic axis, yielding poor visual resolution. Although manufacturers are constantly striving to minimize these distortions, some wearers cannot tolerate the lenses.
The latest technology in progressive lenses is known as FREEFORM or commonly called HIGH DEFINITION. |
