Anatomy
Eyelid opening
- Primarily by levator palpebrae superioris muscle
- Innervated by the superior division of the oculomotor nerve
- Levator palpebrae superioris muscle and superior rectus are innervated by the superior division of the oculomotor nerve.
- During eyelid opening and upward gaze: the tone of the levator and superior rectus must remain relatively equal and constant.
- During forced lid closure there is an inverse relationship between these two muscles such that forced lid closure is accompanied by elevation of the eyes (Bell's phenomenon).
- 2 accessory muscles
- The superior tarsal muscle (Müller's muscle)
- Smooth muscle
- Embedded in the levator muscle
- Inserts on the tarsal plate.
- Innervated by sympathetic fibers.
- Frontalis muscle
- Helps to retract the eyelid in extreme upgaze.
- Innervated by the facial nerve.
Normal eyelid closure
- Normal: due to loss of tone in the levator muscle.
- Forced: due to contraction of the orbicularis oculi muscle, innervated by the facial nerve.
Eyelid Abnormalities
Ptosis
- Paralytic drooping of the upper eyelid.
- Due to
- Third nerve palsy
- Causes complete ptosis (loss of tone in the levator muscle),+
- Accompanied by: pupillary dilatation + diplopia.
- Horner syndrome
- Due to loss of tone in Müller's muscle
- Accompanied by miosis and anhydrosis.
- Myasthenia gravis
- Bilateral ptosis.
- Accompanied by weakness of eyelid closure and diplopia.
Eyelid retraction
- Sclera showing between the iris and the eyelid.
- Due to
- Thyroid ophthalmopathy
- Common cause
- Due to by a pathological shortening of the levator muscle.
- Dorsal midbrain lesion (parinaud)
- Bilateral eyelid retraction, or Collier's sign,
- Accompanied by light-near dissociation
- Unlike thyroid ophthalmopathy, there is no suggestion of lid retraction on downward gaze (Graefe's sign).
- Lower eyelid retraction may be the earliest clinical lid sign of a facial nerve lesion, which is the most common cause of lower eyelid retraction.
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