Etiology: the weakening or loss of upper eyelid muscle function is caused by congenital or acquired factors: congenital (children) is mostly caused by muscular dysplasia or neurodevelopmental disorder; Acquired diseases are usually caused by oculomotor nerve paralysis, levator palpebrae superioris injury, sympathetic diseases, myasthenia gravis, inflammatory swelling of the upper eyelid or new organisms.
Classification: according to the range of the upper eyelid covering the pupil, it is divided into mild, moderate and severe:
The eyelid with mild ptosis covers the pupil in the range of 2 ~ 4 mm,
The range of eyelid covering pupil in moderate ptosis is 4~6mm,
Severe ptosis, the range of eyelid covering pupil is more than 6 mm
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