Progressive lenses

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Progressive lenses, also called progressive addition lenses, progressive power lenses, graduated lenses and varifocal lenses, are corrective lenses used in eyeglasses 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 aberration away from the optic axis, yielding poor visual resolution. Although manufacturers are constantly striving to minimize these distortions, some wearers cannot tolerate the lenses.

Essilor laid a strong claim to have invented varifocals in 1958 with their first design of Varilux lens^{[citation needed]}. Early varifocals were relatively crude designs but modern sophisticated varifocals have gained much greater patient acceptance and include special designs to cater to many separate types of wearer application, for example lenses may be customized for use with computers, or to offer enlarged near and intermediate view areas. over the past years manufacturers have been able to minimize the abberations by using a wide array of mid and high index materials as well as new wave-front freeform technology