====== Ocular Myasthenia Gravis ======

===== Clinical Features =====
  * Triad: Ptosis, Oculomotor paresis and Obicularis oculi weakness
    * **Ptosis** may be unilateral or bilateral
      * Alternating ptosis is specific for this condition
      * **Eyelid fatigue** 
        * Ptosis worsens with prolonged upgaze or upon return to primary gaze
      * **Cogan's lid twitch**
        * After brief but sustained downgaze, a saccade to primary gaze results in the eyelid quickly rising and falling (1 mm or more typically)
      * **Eyelid Curtaining**
        * When lifting the more ptotic eyelid, the contralateral eyelid will droop more because of Hering's law
      * Resting for 5 minutes with the eyes closed will cause improvement in ptosis  
    * Strabismus that fluctuates or appears fatiguable 
      * Any type of strabismus possible
      * prolonged or sustained gaze in the field of action of the affected muscle may show increasing paresis
    * Lagophthalmos is rare
      * attempt to open the eyelid against forced closue- if the eyelid can be opened it suggest obicularis weakness

===== Diagnostic Tests =====
==== Antibody Tests ====
  * **Acetylcholine Receptor Antibody** 
    * sensitivity 50% in Ocular myasthenia vs 90% in Generalized myasthenia
    * The most specific test, no false positives have been reported
  * Muscle specific tyrosine kinase antibodies (MuSK)
    * Rare cares of this antibody present in the setting of ocular myathenia without acetylcholine receptor antibodies
  * LRP4 antibodies
    * 3 cases reported these present in setting of ocular myasthenia
==== Other tests ====
  * **Ice Pack Test**
    * Place a bag of ice on the ptotic lid for 1 minute
    * Immediately asses ptosis when ice removed
    * improvement is transient (<1 min)
    * sensitivity 80% if prominent ptosis present
  * **Tensilon test**
    * Edrophonium- inhibits acetylcholinesterase
    * transiently reverses muscle weakness
    * Sensitivity 85-95%
  * Electrophysiology
    * Repetitive nerve stimlation- reduction in amplitudes with repetitive stimulation
    * Single-fiber EMG- temoral variability of adjacent motor nerve fibers known as "jitter".