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a progressively diminishing ability of the eye to focus, noticeable from middle to old age, caused by loss of elasticity of the crystalline lens
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



diminution of the power of accommodation of the eye due to advancing years. Presbyopia occurs as a result of sclerosing of the crystalline lens, which is unable to increase its curvature to the limit when there is a maximum tension (accommodation); the result is that its refractive power decreases, and the ability to see objects close to the eye is impaired.

Presbyopia begins at age 40 to 45 when eye refraction is normal. When myopia is present, it begins later, and with hyperopia, it comes on earlier. Treatment consists in appropriate selection of glasses for reading and close work. Persons 40 to 45 years of age with normal refraction need a plus lens of 1.0 to 1.5 diopters for reading at a distance of 33 cm. Every five years the refractive power of the lens is increased by 0.5 to 1 diopter. Corresponding corrections in the lens power are made for myopia and hyperopia.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


Diminished ability to focus the eye on near objects due to gradual loss of elasticity of the crystalline lens with age.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.