Ptosis

In planning the restoration of function in a patient with an oculomotor palsy, treatment of ptosis is often particularly problematic. A ptotic lid prevents the patient from having diplopia, and raising it may cause symptoms. However, if any degree of normal binocular vision is to be attained in an affected child, a severe ptosis must be corrected. It is generally preferred to defer ptosis correction until after the eye has been maximally realigned. The degree of residual levator function largely dictates the ptosis procedure of choice. Patients with minimal or no levator function require a frontalis suspension procedure. Before a frontalis suspension is performed, the patient should be examined for the presence of Bell’s phenomenon and for a normal corneal reflex. If either of these is absent, ptosis surgery may be complicated by postoperative corneal drying and subsequent ulceration. The use of a Silastic sling (which is elastic and allows the lids to close) to produce mild lid elevation, together with frequently applied topical lubricant, minimizes this risk.

Treating ptosis surgically in a child with horizontal-gaze lid dyskinesis presents a unique opportunity to surgically correct ptosis by exploiting the process of aberrant regeneration. If the lid of the affected eye elevates during attempted adduction of that eye, then a recess–resect procedure moving the contralateral (unaffected eye) into adduction will create a fixation duress. This, in turn, will necessitate increased innervational tone to maintain fixation with the nonparetic eye in

primary gaze, which will recruit the paretic medial rectus muscle and thereby elevate the ptotic eyelid.195

Trochlear Nerve Palsy

Trochlear nerve palsy is the most common isolated cranial nerve palsy and the most common cause of acquired vertical diplopia (Fig. 6.8).369 The great majority of superior oblique palsies are traumatic or congenital in origin. A vas­ cular, neoplastic, or neurologic etiology is rarely found.572 Amblyopia is rare in isolated acquired trochlear nerve palsy because children can fuse with a compensatory head tilt. The finding of associated amblyopia suggests a congenital origin.

Clinical Anatomy

The trochlear nerve is the smallest and longest of the ocular motor nerves.554 It is the only cranial nerve to emerge on the dorsal surface of the brainstem and the only one to cross entirely. The trochlear nucleus lies caudal to the oculomotor nuclear complex, dorsal to the medial longitudinal fasciculus, and just ventrolateral to the cerebral aqueduct at the level of the inferior colliculus.66 The nucleus gives rise to the nerve fascicle that courses posteroinferiorly around the aqueduct to