replacement of orbital striated muscle by fibrous tissue. Affected children classically present with bilateral upper eyelid ptosis, diffuse ophthalmoplegia, and fixed downgaze with esotropia or exotropia. In some children, the ocular abnormalities are unilateral. The levator is the most common extraocular muscle involved, followed by the inferior rectus and the lateral rectus muscles. Children with CFEOM3 may therefore present with ptosis, exotropia, and a hypotropia from birth that may simulate pupil-sparing congenital third nerve palsy. Aberrant regeneration is now recognized to be a common feature in children with congenital fibrosis syndrome.80 The diagnosis of congenital fibrosis syndrome is suspected by its hereditary character and confirmed by a markedly positive forced duction test and often with genetic testing. As this condition is now classified as a congenital cranial dysinnervation syndrome,553 its nosological distinction with congenital third nerve palsy has blurred.

The distinction between a third nerve palsy and an orbital blowout fracture in the child with head and/or orbital trauma is especially challenging.599 A blowout fracture may produce limited supraduction, infraduction, ptosis, and pupillary dilation (resulting from paralysis of the parasympathetic pupillomotor fibers from injury to the nerve to the inferior oblique muscle or from traumatic mydriasis). In the acute stage of injury, a forced duction test may not reliably distinguish blowout fracture from third nerve palsy, because a positive forced duction test can result from hemorrhage or edema in and around the fibrous septae that connect the inferior rectus and inferior oblique muscle to the periorbita. Furthermore, it is not uncommon for a blowout fracture and a third nerve palsy to coexist.599 Coexistent hemorrhage, edema, soft tissue entrapment, and surgical intervention may mask these associated palsies.418 Occasionally, orbital imaging demonstrates clinically unsuspected blowout fractures in patients with other forms of complicated strabismus.

Because the orbital bones are more flexible in children, pediatric orbital fractures are often of the trapdoor type, (a fracture in which the orbital bones “snap back” causing entrapment of orbital tissues), which requires earlier surgical intervention. In these smaller fractures, soft tissue entrapment is easily overlooked on computed tomography (CT) and is better judged clinically.4 These linear nondisplaced blowout fractures may cause restriction without producing visible signs of entrapment on CT scanning, so it is important to suspect orbital fracture with muscle entrapment in any child with a history of even minor trauma and vertical gaze restriction, regardless of the radiologist’s interpretation of the CT scan. In this setting, careful review of the CT images with direct coronal (not coronal reconstructions from direct axial images) is warranted.124 Neuroimaging studies suggest that the inferior oblique muscle branch of the oculomotor nerve can become incarcerated in a trapdoor fracture causing an inferior oblique muscle paresis.261

One special caveat applies to the debate about whether and when to treat children with this condition. Orbital blowout fractures in children can occasionally stimulate the oculodigital reflex. A patient experiencing the triad of bradycardia, nausea, and syncope following orbital injury should immediately undergo CT with coronal sections. If a trapdoor fracture with incarceration of soft tissue is identified, the fracture should be repaired the same day.519

Internuclear ophthalmoplegia is rare in children.282 It may be unilateral or bilateral and is characterized by an isolated adduction deficit with abducting nystagmus in the contralateral eye. The absence of strabismus in primary gaze distinguishes internuclear ophthalmoplegia from isolated medial rectus involvement secondary to partial third nerve palsy.

Patients with type II Duane syndrome can have an isolated adduction deficit that may mimic a third nerve palsy. Duane syndrome can usually be distinguished from third nerve palsy by its normal vertical ductions and by the retraction of the globe during attempted adduction (although rare cases of electromyographically documented type II Duane syndrome show no retraction).201 Graves orbitopathy has been reported in children but is exceedingly rare.571

Management

Amblyopia

The ability of children to avoid diplopia and blurred visual images by suppressing one eye renders them prone to develop amblyopia from a third nerve palsy. The main mechanism of amblyopia is ocular misalignment, but occlusion by the ptotic lid and defocusing of the image by loss of accommodative tone also contribute.14,15 Elston and Timms158 have shown that children who recover from a third nerve palsy prior to the age of 6 weeks do not develop amblyopia, indicating that there may be a latent period of visual development prior to the onset of the sensitive period. Children beyond the age of 4 years are more likely to experience diplopia and less likely to develop amblyopia. In the remaining sensitive period, the risk of amblyopia must be borne in mind by the physician. Because these children have a period of normal visual experience, their response to amblyopia therapy, both in the recovery of vision and the redevelopment of stereopsis, is usually good. Ing et al243 found that amblyopia, although common in children with oculomotor palsy, usually responds readily to treatment. Part-time patching is recommended while conducting clinical investigations or awaiting spontaneous recovery, provided the lid is at a position or level that allows the child to use the eye. If recovery is incomplete, then amblyopia therapy must be continued while awaiting surgical correction.

Ocular Alignment

Of the three ocular motor nerve palsies, the treatment of third nerve palsy presents the most challenging problem to the strabismus surgeon. Oculomotor palsy is associated with poor visual and sensorimotor outcomes in children younger than 8 years of age.390 Young children with posttraumatic and postneoplastic oculomotor nerve injuries demonstrated the worst ophthalmologic outcomes.390 The only thoroughly satisfactory outcome occurs in children who have enough spontaneous recovery of neural function to regain sensory and motor fusion in all fields of gaze. Those who do not recover spontaneously are left with a complex disorder of static and dynamic ocular motor disturbances in both the horizontal and vertical planes. Multiple strabismus procedures are often necessary to achieve ocular alignment. Surgery rarely results in establishment or restoration of measurable binocular function.497 It is usually impossible to align the eyes in all positions of gaze. The range of outcomes includes diplopia in all gaze positions; single vision with a compensatory head posture but not with a primary head posture; single binocular vision in primary gaze with a normal head posture but diplopia outside relatively narrow range of eye movements; and a more extensive range of single binocular vision with a normal head position but diplopia on extremes of gaze.195

The goals of surgery in treating a third nerve palsy should be (a) to allow single binocular vision in the primary position,

(2) to extend single binocular vision into reading position, (3) to maximize the number of degrees around a primary position in which single binocular vision can be maintained, and

(4) to normalize the appearance of the affected eye. To achieve these goals in children with third nerve palsy, attention has to be given to both horizontal and vertical misalignment and to the lid position. In addition to the risk of creating new ductional deficits with large recess–resect techniques, the surgery may cause anterior segment ischemia that can occur when simultaneously operating on more than two rectus muscles.488,490 In some patients, postoperative intorsion (resulting from associated paresis of the inferior oblique muscle) may hinder fusion and necessitate superior oblique weakening.53

If there is some residual medial rectus function and only moderate horizontal misalignment (15–30 diopters), a recession of the lateral rectus muscle and a resection of the medial rectus muscle may be the simplest and most effective procedure. Alternatively, a very large recession of the contralateral rectus muscle will symmetrize ductions and improve postoperative alignment in some cases. If there is no power of adduction remaining in a patient with a third nerve palsy, a maximum recess–resect procedure may initially bring the eye to primary position, but the eye will gradually become exotropic as the lateral rectus muscle undergoes chronic contraction and the resected medial rectus muscle

elongates.195 In this setting, the superior oblique tendon can be severed nasally and its proximal portion transposed to the insertion of medial rectus muscle to provide a tonic elevation and adduction force that mechanically holds the eye in primary position.195,499 This and other similar fixation procedures527 are performed in combination with a large lateral rectus recession.610 This procedure does little to restore adduction but simply provides an effective mechanical force to prevent recurrent exotropia.364 Some have achieved satisfactory results with primary extirpation of the lateral rectus muscle alone in children who have third nerve palsies and no medial rectus function. Similar success has been reported with lateral rectus muscle disinsertion and reattachment to the lateral orbital wall.383,564 The latter procedure has the advantage of being potentially reversible.

If exotropia is accompanied by a mild (10 diopter or less) vertical misalignment in primary position, the recess–resect procedure can be combined with a vertical transposition of the horizontal rectus muscles in the direction that one wishes to move the eye.85 For example, in a patient with a third nerve palsy with partial recovery resulting in a 20 diopter exotropia and an 8 diopter hypertropia, the lateral rectus muscle could be recessed and the medial rectus muscle resected and both transposed a full tendon width inferiorly in an attempt to correct both the vertical and horizontal misalignment. It may ultimately be necessary to do further surgery on the vertical rectus muscles in this situation, as would certainly be necessary with larger vertical deviations; however, this should be delayed to allow time for anterior segment circulation to be reestablished.

Vertical rectus muscle transposition procedures can also be employed in patients with third nerve palsy and minimal adduction; however, they are less predictable because the vertical rectus muscles are usually weak, limiting their usefulness as candidates for transposition to the medial rectus site. If the lateral rectus muscle has been weakened and transposition of the inferior and superior rectus muscles is contemplated, then it may more safely be done by the technique described by McKeown et al353 to maintain anterior segment perfusion. The use of botulinum in the treatment of third nerve palsy is limited to weakening the lateral or inferior rectus muscle. As in the treatment of sixth nerve palsy (discussed later), oculinum injection may be used in an acute setting to prevent antagonist contracture, or in the setting of a residual postoperative deviation, to try to produce a compensatory contracture of the paretic muscle.

In comparing the efficacy of surgical strategies to treat strabismus resulting from ocular motor palsies, it is important to examine all available objective criteria, including (1) residual deviation in primary position, (2) residual face turn,

(3) postoperative ductions, and (4) field of single binocular vision (which allows for quantitative comparison of surgical outcomes).470