Ptosis





The primary muscle of eyelid elevation is the levator palpebrae (LP), which is innervated by the oculomotor nerve. A secondary muscle (the superior tarsal) is innervated by oculosympathetic nerve fibers arising from the superior cervical ganglion and produces a small amount of eyelid opening that varies with level of arousal and sympathetic tone. The primary muscle of eyelid closure is the orbicularis oculi, which is innervated by the facial nerve.



  • A.

    Initial evaluation should focus on determining if the patient has true ptosis or a ptosis mimic. Eyelid edema and anatomical variants of eye position can give the erroneous impression of ptosis. Facial weakness, such as that seen with Bell palsy, results in an abnormally widened palpebral fissure due to orbicularis weakness. This can give the mistaken impression of contralateral ptosis. Conversely, orbicularis overaction, such as that seen with hemifacial spasm, causes narrowing of the palpebral fissure, but this is not considered ptosis, as the eyelid closure is active, not passive. Eyelid-opening apraxia is a disorder of voluntary eyelid opening of supranuclear origin often seen in progressive supranuclear palsy and other neurodegenerative disorders. Reflexive eyelid opening is normal, and patients can often sustain eyelid opening after briefly elevating their eyelids manually, distinguishing this from true ptosis. A similar phenomenon can be seen with nondominant hemispheric stroke. Hering’s law of equal innervation refers to the fact that an increase in activity of one levator muscle is accompanied by an obligatory increase in activity of the other levator muscle. This is explained by the fact that both muscles are innervated by a single midbrain nucleus. In cases of unilateral primary eyelid retraction (e.g., thyroid eye disease, dorsal midbrain syndrome), eyelid opening decreases in order to minimize eyelid retraction, but because both LP muscles relax, contralateral pseudoptosis occurs. Hering’s law also underlies the phenomena of curtaining (with manual lifting of one eyelid, the other lid comes down or “curtains”).


  • B.

    Eyelid excursion is the distance the upper eyelid margin travels between downgaze and upgaze. It reflects LP function. Reduced eyelid excursion (< 12 mm) indicates levator weakness due to a neurogenic, myogenic, or neuromuscular junction process. In contrast, preserved eyelid excursion (≥ 12 mm) suggests that levator function is normal and that ptosis is due to other causes.


  • C.

    Levator dehiscence-disinsertion is the most common cause of acquired ptosis in adults. It occurs when the LP dehisces from its attachment on the upper eyelid and reinserts more proximally. The lid crease, visualized as a horizontal skin crease on the upper eyelid in downgaze, is defined by the insertion of the LP on the upper eyelid. When the levator dehisces and reinserts more proximally, the lid crease is heightened. Because the levator muscle itself is otherwise normal, eyelid excursion is preserved. Levator dehiscence-disinsertion commonly occurs with advancing age but can be accelerated by repetitive eyelid trauma (e.g., eye rubbing, contact lens wear).


  • D.

    Orbicularis strength can be tested by asking the patient to forcefully close their eyes while the examiner attempts to manually open them.


  • E.

    Horner syndrome is caused by lesions of the oculosympathetic pathway extending from the hypothalamus to the lower cervical and upper thoracic spinal cord, chain, superior cervical ganglion, and internal carotid artery. Causes include brainstem (e.g., lateral medullary infarction) and spinal cord lesions, apical lung tumors (Pancoast syndrome), and carotid dissection. Ptosis in Horner syndrome is mild and accompanied by miosis (pupillary constriction) and anhidrosis.


  • F.

    In addition to the LP, the oculomotor nerve also innervates multiple extraocular muscles (superior, inferior, and medial recti and inferior oblique) and the pupillary sphincter. Therefore, ptosis due to a third nerve palsy is typically accompanied by ophthalmoparesis and sometimes pupillary dilation. Pupillary involvement in a third nerve palsy is more frequently seen in compressive etiologies because the pupillary fibers are located more superficially than the oculomotor fibers and are thus the first to be affected in extrinsic compression. Myasthenia gravis does not affect pupillary function but does cause ophthalmoparesis and can do so in a pattern that may mimic any cranial nerve, nuclear, or internuclear eye movement disorder. Thus, myasthenia gravis should be considered in the differential diagnosis of a pupil-sparing third nerve palsy.


  • G.

    Myasthenia gravis is an autoimmune disorder of neuromuscular transmission. Ptosis and diplopia are extremely common symptoms, classically occurring later in the day with fatigue. About half of patients present with purely ocular symptoms. Of patients presenting with ocular disease, over half will eventually develop axial and limb weakness, usually within 2–3 years of diagnosis. Acetylcholine receptor antibodies are present in only about half of patients with ocular myasthenia gravis, so nerve conduction studies with repetitive stimulation or single fiber electromyography may be needed to confirm the diagnosis. Most inherited and acquired myopathies spare the eyelids due to histologic differences in the extraocular muscles compared to other skeletal muscles. Notable exceptions include mitochondrial disease (chronic progressive external ophthalmoplegia), myotonic dystrophy, and oculopharyngeal muscular dystrophy. Ptosis in myopathies is almost always symmetric, whereas in myasthenia it may be symmetric or asymmetric.


May 3, 2021 | Posted by in NEUROLOGY | Comments Off on Ptosis

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