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Ptosis (from Greek ''Ptosis'' "Blepharoptosis" or πτῶσις, to "fall") is a drooping or falling of the upper eyelid. The drooping may be worse after being awake longer, when the individual's muscles are tired. This condition is sometimes called "lazy eye", but that term normally refers to amblyopia. If severe enough and left untreated, the drooping eyelid can cause other conditions, such as amblyopia or astigmatism. This is why it is especially important for this disorder to be treated in children at a young age, before it can interfere with vision development. ==Causes== Ptosis occurs due to disfunction of the muscles that raise the eyelid or their nerve supply (oculomotor nerve for levator palpebrae superioris and sympathetic nerves for superior tarsal muscle). It can affect one eye or both eyes and is more common in the elderly, as muscles in the eyelids may begin to deteriorate. One can, however, be born with ptosis. Congenital ptosis is hereditary in three main forms.〔(【引用サイトリンク】url=http://www.medigle.de/rw/diagnoses/kongenitaler+Ptosis )〕 Causes of congenital ptosis remain unknown. Ptosis may be caused by damage/trauma to the muscle which raises the eyelid, damage to the superior cervical sympathetic ganglion or damage to the nerve (3rd cranial nerve (oculomotor nerve)) which controls this muscle. Such damage could be a sign or symptom of an underlying disease such as diabetes mellitus, a brain tumor, a pancoast tumor (apex of lung) and diseases which may cause weakness in muscles or nerve damage, such as myasthenia gravis or Oculopharyngeal muscular dystrophy. Exposure to the toxins in some snake venoms, such as that of the black mamba, may also cause this effect. Ptosis can be caused by the aponeurosis of the levator muscle, nerve abnormalities, trauma, inflammation or lesions of the lid or orbit.〔(【引用サイトリンク】 title=Ptosis, Adult )〕 Dysfunctions of the levators may occur as a result of autoimmune antibodies attacking and eliminating the neurotransmitter.〔(【引用サイトリンク】 title=Eye Ptosis Congenital )〕 Ptosis may be due to a myogenic, neurogenic, aponeurotic, mechanical or traumatic cause and it usually occurs isolated, but may be associated with various other conditions, like immunological, degenerative, or hereditary disorders, tumors, or infections Acquired ptosis is most commonly caused by aponeurotic ptosis. This can occur as a result of senescence, dehiscence or disinsertion of the levator aponeurosis. Moreover, chronic inflammation or intraocular surgery can lead to the same effect. Also, wearing contact lenses for long periods of time is thought to have a certain impact on the development of this condition. Congenital neurogenic ptosis is believed to be caused by the Horner syndrome.〔 In this case, a mild ptosis may be associated with ipsilateral ptosis, iris and areola hypopigmentation and anhidrosis due to the paresis of the Mueller muscle. Acquired Horner syndrome may result after trauma, neoplastic insult, or even vascular disease. Ptosis due to trauma can ensue after an eyelid laceration with transection of the upper eyelid elevators or disruption of the neural input.〔 Other causes of ptosis include eyelid neoplasms, neurofibromas or the cicatrization after inflammation or surgery. Mild ptosis may occur with aging. A drooping eyelid can be one of the first signals of a third nerve palsy due to a cerebral aneurysm, that otherwise is asymptomatic and referred to as an oculomotor nerve palsy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ptosis (eyelid)」の詳細全文を読む スポンサード リンク
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