Congenital third CN palsy presents with varied degrees of extraocular involvement. Intraocular musculature is not usually affected in congenital third CN palsy, although pupil constriction may occur on attempted adduction in some cases of aberrant regeneration.^16,17

The involved pupil may even be smaller than that in the uninvolved eye in congenital third CN misdirection syndrome.¹⁸ Although congenital third CN palsies are considered to be benign and isolated, Balkan and Hoyt¹⁹ reported other signs of focal neurologic damage, including pupillary involvement, oculomotor synkinesis, hemiplegia, seizures, and developmental delay. These congenital third CN palsies probably occur as a result of damage to both the peripheral nerve and the brainstem.¹⁹

Balkan and Hoyt found neurologic involvement or developmental delay in 7 of 10 patients studied. Hamed²⁰ described neurologic involvement in 10 of 14 cases with congenital oculomotor palsy, and Tsaloumas and Willshaw²¹ reported 5 of 14 patients with congenital oculomotor palsy with significant neurologic abnormalities, including 2 patients using digital lid elevation to allow fixation with their affected eye.

The degree of involvement of the levator muscle varies, but some function is usually retained. Therefore, ptosis is variable in this form of third CN palsy. The four extraocular muscles innervated by the third CN are also affected in various degrees. However, there is usually some trace at least of weakness of the medial, inferior, and superior rectus muscles and of the inferior oblique muscle. The fourth CN is uninvolved and, consequently, the involved eye is exotropic and hypotropic (Fig. 19-1). Therefore, the clinician should always suspect congenital third CN palsy in an exotropic patient who has one low eye, intact pupillary and accommodation responses, and minimal ptosis of the involved eye with varied degrees of limitation of both elevation and depression in addition to diminished adduction. Many of these patients are able to develop single binocular vision and to maintain a compensatory malposition of the head that allows the alignment of the eyes to serve this purpose. When the eyes are moved into a position in which fusion is not possible, these patients experience diplopia if they have binocular vision with torticollis. Amblyopia of either eye may occur if the patient does not have binocular vision and does not maintain torticollis.

Schumacher-Feero et al²² reported a series of 49 children with third CN palsy, involving 53 eyes, and observed during a follow-up for a mean of 5.5 years. Amblyopia developed in 27 eyes, and at the last follow-up visit, in 56% of affected eyes the visual acuity ranged from 20/15 to 20/40. Binocular function was difficult to restore or to preserve but was significantly improved after surgery. Horizontal alignment was initially good in 6 of 49 patients, improving to 30 with good alignment at their last evaluation. The vertical alignment improved from 24 initially to 35 with good alignment at their last evaluation. Only one child achieved fusion at distance and near after a single recession/resection procedure at 8 months of age. A complete palsy required a mean of 2.3 operations to align the eyes, and a partial third CN palsy required a mean of 1.5 operations over the 5.5-year period. In general, the surgery was a horizontal recession/resection procedure for exotropia, with graded supraplacement of the horizontal rectus insertions for the hypotropia.

The cause of congenital third CN palsy is unknown, but it is presumed to be a result of a developmental defect in either the nuclear or the motor fiber portion of the third CN complex that innervates the levator muscle and the extraocular muscles. It is not an extremely rare motility disorder. We have seen many patients having only unilateral involvement.

As in any third CN palsy, the absence of adduction of the involved eye makes it difficult to determine the intactness of the ipsilateral fourth cranial nerve. Clinically, the method used is to observe the crypts of the iris while the involved eye remains abducted and to ask the patient to look upward and downward. If the fourth CN is intact, the iris markings reveal a conspicuous intorsion as infraduction is attempted and extorsion as supraduction of the involved eye is attempted (Fig. 19-2). Dieterich and Brandt²³ measured ocular torsion and subjective visual vertical tilts in acute and chronic oculomotor, trochlear, and abducens nerve palsies for each eye separately in the primary position with the head held upright. Unexpectedly, ocular torsion was abnormal in only 32% of third and fourth CN palsies involving oblique eye muscles, and normal in all abducens palsies. When measurable, pathologic ocular torsion was low, from 2° to 8°, monocular, involving either the paretic or nonparetic eye. Subjective visual vertical tilts were abnormal in 67% of third and fourth CN palsies, mostly low in amplitude, between 1° and 6°, and involving either the paretic or nonparetic eye, depending on the duration of the palsy. In contrast with acute unilateral brainstem lesions with frequent binocular and conjugate tilts, third and fourth CN palsies cause only minor and unpredictable ocular torsion and subjective visual vertical tilts.

The forced duction test produces a negative result in third CN palsy; this rules out any adhesive phenomenon that limits motility of the eye. The degree of involvement of the third CN determines whether therapy is indicated. Involvement may be so minor and partial that no therapy is necessary, or it may affect only the elevators of an eye and is therefore known as double elevator palsy. Cadera et al²⁴ studied pathophysiology of double elevator palsy in two patients with magnetic resonance imaging (MRI) with volume scanning technique. They found the volume of the superior rectus muscle on the affected side to be less than half that of the normal eye, with other rectus muscles normal, suggesting either congenital hypoplasia or paresis of the affected superior rectus muscle. The inferior oblique muscles could not be evaluated by MRI. After a Knapp procedure in both patients, only minimal superior displacement of the medial and lateral rectus muscles was detectable posterior to the equator of the globe in both patients with MRI.

Double elevator palsy is usually rather complete, and it may also be associated with various degrees of ptosis (Fig. 19-3). The ptosis may be only pseudoptosis because of the hypotropia and because the lid position follows that of the eye. Fixating with the hypotropic eye causes the complete disappearance of the pseudoptosis; however, there may be a small degree of bona fide ptosis in addition to the pseudoptosis. The traction test result is normal in double elevator palsy. Treatment of double elevator palsy involves transposition of the insertions of the horizontal rectus muscles, placing the new insertions immediately adjacent to the insertion of the superior rectus muscle (Fig. 19-4). This does not produce normal elevation beyond the midline level, but it renders considerable improvement in, if not total elimination of, the hypotropia caused by this disorder.

After a full tendon transfer of the lateral and medial rectus muscle for double depressor or double elevator palsy, Knapp obtained an average correction of 38 diopters in the primary position and movement of 25° in the field of action of the paretic muscle group from the primary position.²⁵ In the presence of a poor or absent Bell phenomenon, an accentuated lower lid fold of the hypotropic eye in attempted elevation, and a positive traction test result, Scott and Jackson²⁶ recommend inferior rectus recession only as the initial procedure. With a negative forced traction test result, a full Knapp procedure is advised.

Complete congenital third CN involvement requires surgery for exotropia, hypotropia, and ptosis. Hypotropia is resolved by disinserting the tendon of the superior oblique muscle from the globe, which is tight and contracted. Maximal recession of the lateral rectus and resection of the medial rectus may be sufficient to reposition the involved eye in the horizontal plane satisfactorily. However, if this is inadequate, removing the superior oblique tendon from the trochlea, severing the reflected tendon of the superior oblique muscle from the muscular portion, and attaching the superior oblique muscle to the sclera at the insertion of the medial rectus muscle offer excellent correction of the horizontal defect created by the third CN palsy in the primary position.

This does not create normal adduction of the involved eye but is an effective technique for centering the eye.²⁷ However, following transposition of the superior oblique muscle, when the patient depresses the involved eye, it adducts. Saunders and Rogers,²⁸ who attempted correction of third CN palsy by superior oblique anterior transposition and advancement without trochleotomy, reported unsatisfactory results because of inadequate horizontal alignment, postoperative hyperdeviations, or paradoxical ocular movements. Superior oblique tendon transposition with trochleotomy causes the adherence syndrome, owing to violation of the Tenon capsule, which is unavoidable in removing the superior oblique tendon from the trochlea. Therefore, this procedure is no longer recommended. Scott²⁹ and Gottlob et al³⁰ described anterior transposition of the nasal portion of the superior oblique tendon, 2 to 3 mm anterior to the nasal border of the superior rectus muscle, without trochleotomy. In addition, Gottlob et al performed large recessions of the ipsilateral lateral rectus, and in some patients, a recess-resect procedure on the horizontal rectus muscles of the contralateral eye. Orthophoria was achieved in four patients, a 10 prism diopter (PD) residual exotropia in one patient, and two patients required reoperations because of aberrant regeneration of the oculomotor nerve. In a much larger series, Maruo et al³¹ compiled 280 cases of exotropia secondary to oculomotor palsy, between 1971 and 1993. There were 130 congenital and 150 acquired cases of oculomotor palsy. Surgery was performed 234 times in 138 patients with paralytic exotropia, with transposition of the superior oblique tendon and resection of the medial rectus muscle, with or without recession of the ipsilateral lateral rectus muscle. With a 4-year follow-up in 35 cases, the authors found similar results when transposing the superior oblique tendon in patients with complete palsy and in resection of the medial rectus muscle in patients with incomplete palsy. There was no benefit adding a resection of the medial rectus when the superior oblique transposition was performed. However, recession of the lateral rectus muscle greatly improved the effectiveness of either the superior oblique transposition or the medial rectus resection. Mudgil and Repka³² reviewed retrospectively the ophthalmologic outcome of third CN palsy or paresis in 41 children younger than 8 years of age. Etiologies included congenital in 39%, traumatic in 37%, and neoplastic in 17%. Initial visual acuities were reduced in 71%, and the long-term outcome in the 20 who could be observed during follow-up, for a mean of 3.6 years, was reduced vision in 35% because of amblyopia, and in 25% because of nonamblyopic factors. In the congenital third CN palsy group, all patients improved to normal visual acuity. Despite improved alignment after surgery in 40% (8 of 20) of children with long-term follow-up, none obtained measurable stereopsis. Aberrant reinnervation occurred in 45% (9 of 20). Only 3 patients fully recovered and regained measurable stereopsis, with the etiologies of congenital, neoplastic, and traumatic third CN palsies. Kose et al³³ described an approach to surgical management of total third nerve palsy by a hemi-hangback recession of the lateral rectus muscle and a resection of the medial rectus muscle for exotropia. Depending on the amount of vertical deviation, the horizontal rectus muscle insertions were supraplaced, either alone or in addition to a hemi-hangback recession of the inferior rectus. This technique did not affect the normally functioning superior oblique and lateral rectus muscles.

Because of disruption in sensory fusion mechanisms, Elston³⁴ has recommended a one-stage procedure of maximal lateral rectus recession, medial rectus resection, and simultaneous transposition of insertions to that of the superior rectus. The simplest procedure providing predictable cosmetic improvement has been recommended. Ptosis, however, was not addressed. A frontalis suspension of the ptotic lid is the indicated procedure for the associated ptosis. A synthetic material (e.g., 4-0 Supramid) is ideal because if the cornea cannot tolerate the relatively dry state after the lid is elevated, these synthetic sutures can easily be removed and the cornea not harmed permanently. The surgeon should be aware of the absence of the Bell phenomenon in these patients and be alert to postoperative corneal problems associated with this deficiency.

Acquired third CN palsy may be partial or complete and may involve only the extraocular muscles or both intraocular and extraocular muscles. The pupil is usually spared in third CN palsy associated with diabetes.

Acquired third CN palsy usually occurs rather precipitously with maximal involvement. Within days to weeks, there may be an indication of restoration of third CN function manifest by only partial involvement. Recovery is usually complete by 6 months following onset, and, consequently, no judgment should be rendered regarding the necessity of treatment until after the 6-month interval. Partial or complete recovery can be expected, depending on the cause of the third CN palsy, in 48% of the patients.³ Many times such palsy results from relatively serious intracranial involvement, and this may determine whether therapy is indicated. Minor head trauma may produce isolated oculomotor nerve palsy in the presence of a normal CT, normal MRI, and normal magnetic resonance angiography (MRA).³⁵ A case of mild head trauma created a complete left third nerve palsy, with normal CT and MRI of the brain and a normal CT of the orbit. Because of only partial recovery with time and with botulinum toxin, transposition surgery was required to reduce the strabismus.³⁶ Mark³⁷ recommends MRI evaluation of patients with third CN palsy to include proton density and T2-weighted images through the brain in axial section, to study the brainstem for nuclear lesions, along with thin section T1-weighted images in the coronal and axial planes to evaluate cisternal, cavernous, and orbital segments of the third nerve. Gadolinium diethylenepentaminetetraacetic acid has also been found helpful in evaluation of third CN palsy. In posttraumatic third CN palsies, use of gradient echo images to detect hemorrhage is helpful. Ischemia of the oculomotor nerve causes most cases of nontraumatic oculomotor nerve palsy.³⁸ MRI and lumbar puncture are helpful in diagnosing cases caused by inflammatory or neoplastic meningitis. A cerebral aneurysm, which can be fatal, can be diagnosed by cerebral angiography, but this test has a 1% to 2% morbidity and mortality rate. Magnetic resonance angiography is a variant of MRI that highlights blood vessels; however, it is only 95% accurate in detection of aneurysms. Trobe³⁸ therefore concludes that because pupil involvement occurs in 96% with aneurysms, and if anisocoria exceeds 2.0 mm, that catheter angiography is justified. In a series³⁹ of 148 patients with posterior communicating aneurysm, 74 (50%) had concurrent unilateral oculomotor palsy. All patients had a craniotomy after the diagnosis using whole brain digital subtraction angiography. Surgery involved simple pedicle clipping of the aneurysm for the 40 patients in group A, and the 34 patients in group B had pedicle clipping and decompression of the oculomotor nerve. Surgery was timed at within 14 days from diagnosis, from 14 to 30 days, or 30 to 90 days in both groups. In both groups, all 35 patients undergoing surgery within 2 weeks had complete recovery. Four patients in group A and three in group B had incomplete recovery; therefore in group A 90% had complete recovery and 10% incomplete recovery, and in group B 91% had complete recovery and 9% incomplete recovery. There was no correlation found between decompression of the oculomotor nerve, either puncture or excision of the aneurysm, and postop recovery time.

The causes can be classified as follows:

VII. M.

Partial third CN palsy in the form of isolated inferior rectus paresis may be the presenting sign of myasthenia gravis, with sudden onset of diplopia.⁷⁵ A rare inferior division third nerve paresis involving the pupil caused by an intraorbital dural arteriovenous malformation has been reported.⁴⁰ The oculomotor nerve aberrant regeneration or misdirection syndrome is believed to result from extensive and haphazard growth that characterizes the regeneration of injured nerve fibers.^18,34 The third CN misdirection syndrome includes the following.¹⁸

Miller and Lee⁸² described adult-onset acquired oculomotor nerve paresis with cyclic spasms in relation to ocular neuromyotonia in two patients, years after irradiation for intracranial tumors. Findings included unilateral eyelid retraction, ipsilateral esotropia with limited abduction during the spastic phase and with ipsilateral ptosis, exotropia, and variable limited adduction during the paretic phase. The cause of cyclic oculomotor paresis is usually unknown, and most authors speculate some element of aberrant regeneration after nuclear or nerve damage.⁸³ In a case of third CN palsy with trigeminal sensory loss caused by herpes zoster, Quisling et al⁴¹ reported results of the brain MRI, which demonstrated enhancement and thickening of the cisternal and cavernous portions of the right third cranial nerve, and FLAIR MRI revealed high signal intensity in the right posterolateral medulla, consistent with presumed involvement of the trigeminal nucleus and tract. Oculomotor tremor (OMT) is a high-frequency small tremor of the eyes first described as one of the fixational eye movements in 1934 by Adler and Fliegelman.⁸⁴ Bolger et al⁸⁵ found reduced or absent OMT in six adult cases of acquired third nerve palsy, suggesting that innervation of the extraocular muscles is required for normal OMT activity and therefore OMT has a neurogenic origin.

Treatment involves relief of the patient’s diplopia, which usually is not a problem in complete third CN paralysis because of the associated ptosis covering the pupil. However, in partial involvement, the lid may sufficiently clear the pupillary space so that diplopia is a problem. Occlusion therapy is the best solution for the patient’s diplopia. The patient usually wishes to have the involved eye occluded rather than the uninvolved eye. Surgery is indicated for associated strabismus and ptosis if the patient’s general condition permits it and if a significant residual paralysis is present 6 months after onset of third CN palsy. The surgery described for congenital third CN palsy is also applicable for acquired third CN palsy. Kushner⁸⁶ described surgical treatment in five patients with the rare finding of paralysis of the inferior division of the third CN. Clinical findings included a large exotropia and hypertropia of the affected eye, intorsion, and internal ophthalmoplegia. As described by Knapp,⁸⁷ Kushner performed a superior oblique tenotomy along with transposing the superior rectus toward the insertion of the superior border of the medial rectus, following the spiral of Tillaux and transposing the lateral rectus toward the lateral border of the inferior rectus, following the spiral of Tillaux. In follow-up lasting between 3 and 10 years, all patients maintained satisfactory eye alignment and were free from diplopia in the primary position. In the presence of oculomotor palsy with aberrant regeneration, surgery on the nonparetic eye may be indicated.⁸⁶ The eye deviation is measured with the dominant eye fixating, and on the contralateral, nonparetic eye, a lateral rectus recession and medial rectus resection is performed, along with downward transposition of the horizontal rectus muscles to offset the vertical deviation.