Incomitant strabismus

MANAGEMENT/TREATMENT

Initial ophthalmic treatment for patients with acquired 3rd nerve palsy involves relief of diplopia. If there is complete 3rd nerve palsy, the associated complete ptosis will cover the pupil and prevent diplopia. However, in partial 3rd nerve palsy, the lid may not cover the pupillary space, so that diplopia may remain a problem. Occlusion therapy is then the best solution to the diplopia. In children young enough to develop amblyopia, the patch should be alternated so that the affected eye will continue to develop normal vision.

Surgery to correct acquired 3rd nerve palsy should be postponed for several months after the onset of the condition when possible. If the ptosis is complete and the eyelid cannot open, early ptosis surgery may be needed in younger children in order to prevent the development of amblyopia.

PROGNOSIS

Many patients with acquired 3rd nerve palsies will show improvement with time. Those patients with congenital palsies may be given limited binocular vision with early treatment. Multiple procedures are often required to achieve alignment in straight-ahead gaze.

Fourth nerve palsy

ETIOLOGY

A fourth nerve palsy can be congenital or acquired. Because the 4th nerve has a long intracranial course, it is susceptible to damage resulting from head trauma. In children, however, 4th nerve palsies are more frequently congenital than traumatic.

CLINICAL PRESENTATION

A palsied 4th nerve results in weakness in the superior oblique muscle, which causes an upward deviation of the eye, a hypertropia. Because the antagonist muscle, the inferior oblique, is relatively unopposed, the affected eye demonstrates an upshoot when looking toward the nose. Children typically present with a head tilt to the shoulder opposite the affected eye, their chin down and their face turned away from the affected side. This head position places the eye away from the area of greatest action of the affected muscle and therefore minimizes the deviation and the associated double vision. Long-standing head tilts may lead to facial asymmetry. Because the abnormal head posture maintains the child’s ocular alignment, amblyopia is uncommon. As no abnormality exists in the neck muscles, attempts to correct the head tilt by exercises and neck muscle surgeries are ineffective. Recognition of a superior oblique paresis can be difficult because deviation of the head and the eye may be minimal.

DIAGNOSIS

The pattern of strabismus seen in a patient with a 4th nerve palsy is diagnostic. The deviation increases when looking to the unaffected side and when the head it tilted to the same side (54–56). The ‘three step test’ allows for the diagnosis to be made in the vast majority of cases. Sometimes there can be a question as to whether the deviation is of new onset or just newly discovered. The presence of facial asymmetry and/or a long-standing head posture seen in old photographs can often help to answer this question.

MANAGEMENT/TREATMENT

Eye muscle surgery is indicated in order to improve the ocular alignment and eliminate the abnormal head posture. In cases of traumatic palsy, treatment is delayed until there is lack of spontaneous resolution, which will occur in a majority of cases.

PROGNOSIS

Surgery for both congenital and traumatic 4th nerve palsies carries an excellent prognosis for improvement of both the associated torticollis and improving the field of single binocular vision.

Sixth nerve palsy

ETIOLOGY

Acquired 6th nerve palsies in childhood can be an ominous sign because the 6th nerve is susceptible to increased intracranial pressure associated with hydrocephalus and intracranial tumors. Other causes of 6th nerve defects in children include trauma, vascular malformations, meningitis, and Gradenigo syndrome. A benign 6th nerve palsy, which is painless and acquired, can be noted in infants and older children. This is frequently preceded by a febrile illness or upper respiratory tract infection and may be recurrent. Complete resolution of the palsy is usual. Although not uncommon, other causes of acute 6th nerve palsy should be eliminated before this diagnosis is made.

CLINICAL PRESENTATION

A 6th nerve palsy produces markedly crossed eyes with limited ability to move the afflicted eye

laterally (57–59). Children frequently may present with their head turned toward the palsied muscle, a position that helps preserve binocular vision. The esotropia is largest when the eye is moved toward the affected muscle.

DIFFERENTIAL DIAGNOSIS

Congenital 6th nerve palsies are rare. Decreased lateral gaze in infants is often associated with other disorders, such as congenital esotropia or Duane’s retraction syndrome. In neonates, a transient 6th nerve paresis can occur; it usually clears spontaneously by 6 weeks. Increased intracranial pressure associated with labor and delivery may be the contributing factor.

MANAGEMENT/TREATMENT

As with other forms of traumatic cranial nerve palsies, surgical treatment is delayed until there is no sign of spontaneous improvement. Occlusion can be used for relief of diplopia. If the deviation does not improve with time, strabismus surgery may be warranted. If there is some function of the lateral rectus muscle, standard strabismus surgery may be used. If there continues to be complete absence of lateral rectus function, a transposition procedure may be needed in which the inferior and superior rectus muscles are moved next to the lateral rectus muscle to generate outward tension on the eye.

PROGNOSIS

Most cases of 6th nerve palsy will resolve with time. For those that do not, surgery is effective in eliminating the deviation in straight-ahead gaze but often will not improve the lateral movement of the eye.