白內障的成因!!20...20...

白內障

白內障是種眼睛晶狀體發生混濁的疾病，是首位致盲性眼病，白內障的流行情況各地區有很大的差異。一般來說，隨着年齡的增長，白內障的發病率逐漸提高。

晶狀體的混濁位置可以在皮質、核、前囊或者後囊等處。晶狀體的混濁不一定影響視力。出現在視軸上的混濁對視力的影響較大，例如後囊下的混濁，由於其處於眼球這個光學系統的節點處，所以即便是較小的混濁也對視力有較大的影響。

典型的白內障的臨床表現是漸進性視力下降，由於晶狀體的密度變化，還可能伴有近視度數加深，單眼復視（單眼看東西時出現多個物像）等癥狀。一般不伴有眼紅眼痛。目前雖然有許多藥物，但尚無藥物可以使白內障的進程逆轉。所以真正可以使患者視力恢復的治療仍是手術治療。

手術的目的是為了去除已經混濁的晶狀體，並植入人工晶狀體以提高患者的視力。以前由於手術技術的限制，皮質型白內障的手術需要到成熟期才可以進行，此時患者已經基本沒有視力。目前白內障手術的技術已經突破此限制，其適應症大大放寬。

分類及成因

．老年性白內障
．皮質型白內障
．核型白內障
．先天性白內障
．外傷性白內障
．併發性白內障
．代謝性白內障
．中毒性白內障
．後發性白內障

由於水晶體的化學成分改變而導致混濁，其中以老化所造成的老年性白內障最為常見。依不同類型的白內障造成原因如下：

．老年性白內障：由於長期紫外線的傷害及組織的老化，導致水晶體變硬而混濁所致，所謂人老「珠」黃，指的就是這一型的白內障，最早在四十歲左右即可發生。

．先天性白內障：可能因為遺傳或者是胎兒時期的感染，在出生時即已發生水晶體混濁。

．外傷性白內障：眼睛受傷也可造成白內障，舉凡撞擊、穿刺傷、電擊、高熱、化學藥品灼傷等，皆可能傷及水晶體。

．續發性白內障：可續發於眼疾或全身性疾病，如青光眼、虹彩炎、糖尿病等，或是受某些特定的感染、藥物誘導，如皮質類固醇。

症狀主要症狀為無痛無癢的進行性視力減退，會覺得有一層毛玻璃擋在眼前。其他症狀包括，複視、畏光、眩光、色彩失去鮮明度，和經常需要更換眼鏡等症狀。水晶體也可能吸收水分而增厚，導致近視者度數加深，而老花眼者閱讀書報反而不需戴眼鏡，以為得到眼睛的「第二春」。當視力再也無法以更換眼鏡度數來改善時，就到了必須積極治療的時候。

Cataract

A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Early in the development of age-related cataract the power of the lens may be increased, causing near-sightedness (myopia), and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss and are potentially blinding if untreated.

2008-11-03 20:51:32 補充：
A senile cataract, occurring in the aged, is characterized by an initial opacity in the lens, subsequent swelling of the lens and final shrinkage with complete loss of transparency.

2008-11-03 20:51:44 補充：
Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian cataract, which can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma.

2008-11-03 20:51:58 補充：
Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly.

2008-11-03 20:52:07 補充：
Such spontaneous posterior dislocations (akin to the historical surgical procedure of couching) in ancient times were regarded as a blessing from the heavens, because some perception of light was restored in the cataractous patients.

2008-11-03 20:52:18 補充：
Cataract derives from the Latin cataracta meaning "waterfall" and the Greek kataraktes and katarrhaktes, from katarassein meaning "to dash down" (kata-, "down"; arassein, "to strike, dash").

2008-11-03 20:52:36 補充：
As rapidly running water turns white, the term may later have been used metaphorically to describe the similar appearance of mature ocular opacities. In Latin, cataracta had the alternate meaning "portcullis",

2008-11-03 20:53:01 補充：
so it is also possible that the name came about through the sense of "obstruction". Early Persian physicians called the term nazul-i-ah, or 'descent of the water' - vulgarised into waterfall disease or cataract - believing such blindness to be caused by an outpouring of corrupt humour into the eye.

2008-11-03 20:53:15 補充：
In dialect English a cataract is called a pearl, as in "pearl eye" and "pearl-eyed".

Causes

Cataracts develop from a variety of reasons, including long-term exposure to ultraviolet light, exposure to radiation, secondary effects of diseases such as diabetes, hypertension and advanced age,

2008-11-03 20:53:34 補充：
or trauma (possibly much earlier); they are usually a result of denaturation of lens protein. Genetic factors are often a cause of congenital cataracts and positive family history may also play a role in predisposing someone to cataracts at an earlier age,

2008-11-03 20:53:43 補充：
a phenomenon of "anticipation" in pre-senile cataracts. Cataracts may also be produced by eye injury or physical trauma. A study among Icelandair pilots showed commercial airline pilots as three times more likely to develop cataracts than people with non-flying jobs.

2008-11-03 20:53:53 補充：
This is thought to be caused by excessive exposure to radiation coming from outer space. Cataracts are also unusually common in persons exposed to infrared radiation, such as glassblowers who suffer from "exfoliation syndrome".

2008-11-03 20:54:02 補充：
Exposure to microwave radiation can cause cataracts.

Cataracts may be partial or complete, stationary or progressive, hard or soft.

Some drugs can induce cataract development, such as Corticosteroids and Ezetimibe[citation needed] and Seroquel.

2008-11-03 20:54:08 補充：
There are various types of cataracts, e.g. nuclear, cortical, mature, and hypermature. Cataracts are also classified by their location, e.g. posterior (classically due to steroid use) and anterior (common (senile) cataract related to aging).

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白內障的成因？
晶狀體會隨著年齡老化，這就是白內障形成的主因，另外糖尿病、外傷、藥物、還有先天性因素都能引致白內障
Cataract origin?
The crystalline experience gets older along with the age, this is a principal factor which cataract forms, moreover diabetes, the flesh wound, the medicine, also have the congenital factor all to be able to bring about cataract