presbyopia


presbyopia
presbyopic /prez'bee op"ik, pres'-/, adj.
/prez'bee oh"pee euh, pres'-/, n. Ophthalm.
farsightedness due to ciliary muscle weakness and loss of elasticity in the crystalline lens.
[1785-95; < Gk presby- (comb. form of présbys old, old man) + -OPIA]

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      loss of ability to focus the eye sharply on near objects as a result of the decreasing elasticity of the lens of the eye. The eye's ability to focus on near and far objects—the power of accommodation—depends upon two forces, the elasticity of the lens of the eye and the action of the ciliary muscle (ciliaris muscle) (a roughly ring-shaped muscle that encircles the lens and is attached to it by suspensory ligaments). When the ciliary muscle is relaxed, the ring enlarges away from the lens and the suspensory ligaments are tautened, flattening the lens into a shape suitable for viewing distant objects. When the muscle contracts, the ligaments are loosened, and, because of the elasticity of the lens, the surface of the lens—particularly the front surface—becomes more curved, in keeping with viewing near objects. Ordinarily the lens gradually becomes less elastic (it hardens) with age, so the power of accommodation is lost progressively. The loss is most rapid in the decade of the 40s, the age when most people become aware of difficulty in performing a task, such as reading, that requires near focusing; this can be helped with corrective lenses.

      Accommodation may also be lost temporarily as a result of paralysis of the ciliary muscle. With this paralysis, which can occur from the action of certain toxins and medications, the muscle cannot contract, and the surface of the lens is prevented from becoming more convex.

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Universalium. 2010.

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Look at other dictionaries:

  • Presbyopia — is a condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the… …   Wikipedia

  • Presbyopia — Pres by*o pi*a[NL., from Gr. ? old, n., an old man + ?, ?, the eye.] (Med.) A defect of vision consequent upon advancing age. It is due to rigidity of the crystalline lens, which produces difficulty of accommodation and recession of the near… …   The Collaborative International Dictionary of English

  • presbyopia — (n.) far sightedness brought on by age, 1793, Modern Latin, from Gk. presbys old man (see PRESBYTERIAN (Cf. Presbyterian)) + opia, from ops eye (see EYE (Cf. eye) (n.)) …   Etymology dictionary

  • presbyopia — [prez΄bē ō′pē ə, pres΄bē ō′pē ə] n. [ModL < Gr presbys, old (see PRIEST) + ōps, EYE] a form of farsightedness occurring after middle age, caused by a diminished elasticity of the crystalline lens presbyope [prez΄bēōp΄, pres΄bēōp΄] n.… …   English World dictionary

  • 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… …   Medical dictionary

  • presbyopia — noun Etymology: New Latin, from Greek presbys old man + New Latin opia Date: 1793 a visual condition which becomes apparent especially in middle age and in which loss of elasticity of the lens of the eye causes defective accommodation and… …   New Collegiate Dictionary

  • presbyopia — noun Inability of the eye, due to ageing, to focus on nearby objects. Ant: myopia …   Wiktionary

  • PRESBYOPIA —    diminution of sight due to age, occurring usually about forty five, when near objects are less distinctly seen than distant, an affliction due to the flattening of the lens …   The Nuttall Encyclopaedia

  • presbyopia — prezbɪ əʊpɪə n. far sightedness, loss of the ability to see nearby objects clearly (due to age) …   English contemporary dictionary

  • presbyopia — [ˌprɛzbɪ əʊpɪə] noun long sightedness caused by loss of elasticity of the lens of the eye. Derivatives presbyopic adjective Origin C18: mod. L., from Gk presbus old man + ōps, ōp eye …   English new terms dictionary


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