Pathophysiology is congenital agenesis of the sixth nerve nucleus and innervational misdirection of part of the medial rectus nerve to the lateral rectus muscle. This results in limited abduction and co-contraction of the medial and lateral recti on adduction. The co-contraction causes the globe to retract causing lid fi ssure narrowing on adduction. If the medial and lateral recti receive the same reciprocal innervation the eye will rest in primary position (equal). This results in a stand-off with equal medial and lateral forces so there is limited abduction and adduction or Duane’s type 3 syndrome. In cases where the lateral rectus muscle receives more innervation an exotropia Duane’s type 3 syndrome occurs. In most cases the medial rectus muscle gets most of the medial rectus nerve so the resting eye position is in adduction. This is esotropia Duane’s syndrome type 1 (limited abduction, intact adduction). Duane’s type 2 is characterized as good abduction with poor adduction. These cases are very rare (if they exist at all), and most cases are actually Duane’s type 3. Synergistic divergence is a rare type of Duane’s syndrome with abduction on attempted adduction. The lateral rectus muscle receives almost all the innervation from the medial rectus nerve, and there is agenesis of the sixth nerve nucleus.1 Duane’s syndrome is usually sporadic without systemic manifestations, however, it can be familial or associated with systemic disease (Goldenhar syndrome, Klippel-Feil syndrome, and intrauterine thalidomide exposure).
KeywordsRectus Muscle Lateral Rectus Medial Rectus Superior Rectus Inferior Rectus
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