abducens nerve palsy

Sixth nerve palsy

Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI (the abducens nerve), which is responsible for causing contraction of the lateral rectus muscle to abduct (i.e., turn out) the eye. The inability of an eye to turn outward results in a convergent strabismus or esotropia, of which the primary symptom is diplopia (commonly known as double vision), in which the two images appear side-by-side. Thus, the diplopia is horizontal and worse in the distance. Diplopia is also increased when looking at the affected side. It is partly caused by overaction of the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye to the left or right. The condition is commonly unilateral but can also occur bilaterally. The unilateral abducens nerve palsy is the most common isolated ocular motor nerve palsies.