Blepharoptosis, commonly spoken of ophthalmologically as ptosis, is the inability to raise the upper lid owing to paralysis or paresis of the levator palpebrae superioris muscle. Some congenital cases, especially those which are accompanied by a paralysis of the superior rectus, have an anatomic defect present which is not purely innervational or paretic.
Ptosis may be congenital, may follow trauma, may continue as a part of the residuals of an inflammatory condition of the orbit or may be a part of a complete or incomplete external ophthalmoplegia, either central or peripheral in origin. Surgical ptosis should be considered as any one of these cases which is stationary, which cannot be corrected by any medical treatment and which impairs vision. Such a degree simply means that the weakened muscle is unable to raise the lid against the resistance of the orbicularis palpebrae muscle plus the weight of the lid itself. Cicatrices
SPAETH EB. PTOSIS AND ITS SURGICAL CORRECTION. JAMA. 1937;109(23):1889–1894. doi:10.1001/jama.1937.02780490027008