As an individual ages, their ocular or crystalline lens successively loses its ability to focus on near objects.
This change in visual capacity is referred to as sight ageing reduction or presbyopia. Today there are three ways of re-configuring sight ageing using contact lenses: correction with multi-focal lenses, with progressive lenses or with a technique called mono-vision.
Technological advances in the 20th and 21st centuries have made lenses available that provide adequate distance and near correction to most presbyopic CL wearers.
Bifocal lenses contain two distinct prescriptions, one for sharp focus at a distance and the other for adequate focus when viewing objects nearby. These two prescription regions are clearly demarcated in bifocal lenses, with a line separating the distance prescription in the upper region from that of the “addition” or reading prescription in the lower part of the lens.
Multifocal lenses, also referred to as progressive power or graduated lenses, enable many CL wearers to shift focus smoothly from distant to near objects. Concentric rings or differing aspheric designs with varying prescriptions in the lens allow light to simultaneously be focused on the retina from objects viewed at a range of distances. After a short period of adjustment to this type of correction, the customer’s visual neural pathways process these signals so that she automatically selects the power needed to sight a distant, middle-distance or near object clearly. Modern graduated lenses are often customized to the wearer's work environment.
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