- Presbyopia
- The loss of the eye's ability to change focus to see near objects. The reasons for this loss of the power of accommodation are not yet fully known. It is conventionally said to be due to the lens becoming less elastic with time. Presbyopia is associated with aging. It occurs in everyone. The first sign is often the need to hold reading material farther away. The lens of the eye and the muscle that surrounds it are like atomic clocks, slowly ticking with such precision that a person's age can be determined by measuring their ability to focus close up. Children can normally focus on objects an inch or so (a few centimeters) from their eyes. They lose that ability as teenagers. By age 45 or so, when the eyes can focus no closer than a yard (a meter) or two away, almost everyone needs glasses to read a newspaper or thread a needle. The word "presbyopia" comes from the Greek for "elderly vision."
* * *The physiologic loss of accommodation in the eyes in advancing age, said to begin when the near point has receded beyond 22 cm (9 inches). [presby- + G. ops, eye]
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pres·by·opia .prez-bē-'ō-pē-ə, .pres- n a visual condition which becomes apparent esp. in middle age and in which loss of elasticity of the lens of the eye causes defective accommodation and inability to focus sharply for near vision* * *
n.difficulty in reading at the usual distance (about one foot from the eyes) and in performing other close work, due to the decline with age in the ability of the eye to alter its focus to see close objects clearly. This is caused by gradual loss of elasticity of the lens of the eye which thus becomes progressively less able to increase its curvature in order to focus on near objects.* * *
pres·by·opia (pres″be-oґpe-ə) [presby- + -opia] hyperopia and impairment of vision due to advancing years or to old age; it is dependent on diminution of the power of accommodation from loss of elasticity of the crystalline lens, causing the near point of distinct vision to be removed farther from the eye. Abbreviated Pr. presbyopic adj
Medical dictionary. 2011.
