الفهرس 
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Abstract
Ptosis or drooping of the upper eyelid is the most common lid
malposition in children. It accounts for over 50% of lid malposition encountered in clinical practice in the adult population and is the most popular surgically correctable lid disorder. It can be divided into a large group of congenital (70%) and a smaller group of acquired ptosis (30%).
The most common cause of congenital ptosis is myogenic due to the improper development of the levator muscle. Acquired ptosis can be further sub-divided into the following ; neurogenic, myogenic, aponeurotic, mechanical, and traumatic. Most cases of acquired ptosis are secondary to aponeurotic causes such as involutional changes, a disinsertion, or dehiscence which reduce its ability to lift the eyelid.
In most cases of congenital ptosis, a droopy eyelid results from a localized myogenic dysgenesis, rather than normal muscle fibers, fibrous and adipose tissues are present in the muscle belly, diminishing the ability of the levator to contract and relax. therefore, the condition is commonly called congenital myogenic ptosis. The Congenital ptosis also occurs when innervation to the levator is interrupted through neurologic or neuromuscular junction dysfunction.
The levator muscles of patients with congenital ptosis are dystrophic. the levator muscle and the aponeurosis tissues appear to be infiltirated or replaced by fat and fibrous tissue. in severe cases , little or no striated muscle can be identified at the time of surgery. this suggests that congenital ptosis is secondary to local developmental defects in muscle structure .
Congenital ptosis may occur through autosomal dominant inheritance. Common familial occurrences suggest that genetic or chromosomal defects are likely.
The majority of children with congenital ptosis have a developmental myopathy of the levator muscle. The ptosis is present at birth and remains stable throughout life . Levator function is decreased in proportion to the severity of the ptosis.
The most important aspects of the ptosis patients care are the preoperative history, ocular examinations, ptosis assessement and documentations.
One can apply the surgical principles most likely to be successful only after obtaining this information and considering it properly.
Minimal or mild ptosis is 2 mm or less, moderate ptosis is 3 to 4 mm, and severe ptosis is 4 mm or greater.. The levator excursion is the best clinical test for levator function. It is documented in millimeters. Levator excursion of 10 mm or greater is considered good function, 5 to 9 mm of excursion is fair function, and 4 mm or less is poor function.