Progressive lens

Progressive lens are a type of optical lens used in eyeglasses to correct presbyopia and other disorders of accommodation. They are characterised by a gradient of increasing lens power, added to the wearer's correction for the other refractive errors. The gradient starts at the wearer's distance prescription, at the top of the lens and reaches a maximum addition power, or the near prescription, at the bottom of the lens. The length of the progressive power gradient on the lens surface depends on the design of the lens, with a final addition power between 0.75 and 3.50 dioptres for most wearers. The addition value prescribed depends on the level of presbyopia of the patient. In general the older the patient, the higher the addition.

History

The concept of progressive lens has been around since the late 19th century, but it was not until 1959 that the first commercially viable solution was developed by Bernard Maitenaz, who was working for the French company Sociedad Española de Óptica (SEOR), later to become Essilor. The lens, commercially known as Varilux, has been continually improved and remains a market leader.

Design

Progressive lenses are designed to provide a natural correction of presbyopia by smoothly varying the lens power to provide clear vision at all distances. The lens power is determined by the specific needs of the wearer, and can be adjusted to suit specific tasks, such as reading, using a computer, or driving.

Advantages and Disadvantages

The main advantage of progressive lenses is the ability to provide clear, seamless vision at all distances. This eliminates the need for separate glasses for distance and reading, and allows the wearer to perform all tasks without changing glasses. However, some people may experience difficulty adapting to these lenses, and may experience a "swim" effect due to the changing lens power. This can usually be overcome with time and practice.

See Also

• Bifocal lens
• Trifocal lens
• Presbyopia
• Refractive error

References

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