Describe ptosis with its types and management.

Ptosis

• Ptosis is drooping of the upper eyelid below its normal position.
• The upper lid normally covers the top 1 to 2 mm of the cornea, and the palpebral fissure measures 9 to 10 mm.
• The four measurements that determine management, and each must be recorded: the palpebral fissure height; the margin-reflex distance 1 (MRD1), from the corneal light reflex to the upper lid margin, normally 4 to 5 mm, which is the most useful single measure; the levator function, measured from downgaze to upgaze with the brow held, and graded good (over 8 mm), fair (5 to 7 mm) and poor (under 4 mm) — this determines the operation; and the upper lid crease position, which is absent or high in aponeurotic ptosis
• Congenital ptosis — from dysgenesis of the levator muscle, which is replaced by fibroadipose tissue. It is characteristically unilateral, with poor levator function, an absent lid crease, and lid lag on downgaze — the lid of the affected side sitting higher on downgaze, which is the reverse of acquired ptosis and is diagnostic
• The urgent question in a child is amblyopia: from deprivation if the pupil is covered, or more often from induced astigmatism from the lid pressing on the cornea, and from anisometropia. Surgery is deferred to 3 to 5 years unless the visual axis is occluded, in which case it is done early
• MARCUS GUNN jaw-winking — a congenital synkinesis in which the ptotic lid elevates on chewing, sucking or moving the jaw to the opposite side, from aberrant innervation between the pterygoid and levator. It is present in a small proportion of congenital ptosis, and must be looked for by asking the child to chew, since it alters the operation entirely
• Acquired — aponeurotic (involutional) is much the commonest: dehiscence or thinning of the levator aponeurosis with age, after cataract surgery, from contact lens wear or from chronic rubbing. Levator function is good and the lid crease is high or absent, and the lid is thin with the iris visible through it
• Acquired — neurogenic: third nerve palsy (complete ptosis, eye down and out, pupil); HORNER syndrome (mild ptosis of 1 to 2 mm from Muller muscle, with miosis and reverse ptosis of the lower lid); and myasthenia gravis