Isolated Congenital Ptosis
The majority of congenital ptosis cases represent an isolated eyelid malposition, absent other ocular or systemic associations. The ptosis can be unilateral or bilateral and is typically noticed shortly after birth. It is generally considered to be a non-progressive condition with persistent ptosis that is not altered with eye movement or innervation of other cranial nerves. Sometimes a familial element is present, but a gene responsible for bilateral congenital ptosis has yet to be identified.
The unifying clinical feature of isolated congenital ptosis is poor levator function. The etiology of this dysfunction is not clear, and there has been debate as to whether this represents a primary muscular or primary neurologic problem. There is some evidence that supports a neurological explanation, namely that the failure to properly innervate the developing levator palpebrae results in poor development of the muscle (McMullan 2006). The outcome of this developmental insult is the creation of a dysgenic levator palpebrae muscle in which the normal striated muscle fibers are replaced with fatty or fibrotic tissue, especially in the anterior portion of the muscle (Baldwin 2002). The dysgenic muscle can neither contract nor relax normally: The clinical consequence is poor eyelid elevation on upgaze and eyelid lag on downgaze.
While most patients with isolated congenital ptosis have no ocular motility deficits, some patients have associated ipsilateral superior rectus weakness (Beard 1976). This is thought to be secondary to a combined dysgenesis of the levator/rectus complex, also as a result of a developmental insult.