Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006

without passing a posterior suture. Union of the superior and lateral rectus has also been described.

SPECIFIC TYPES OF PARALYTIC

STRABISMUS

Sixth Nerve Palsy

A persistent, isolated, congenital sixth nerve palsy is extremely rare; however, newborns may have a transient sixth nerve palsy that resolves spontaneously over a few days to a few weeks. A common cause of isolated acquired sixth nerve palsy in early childhood is postviral inflammatory neuropathy, which may occur 1 to 3 weeks after a viral illness or immunization or spontaneously without obvious cause. These patients should be followed closely to monitor their improvement and watch for the development of amblyopia. Improvement usually occurs within 6 to 10 weeks. After viral or idiopathic causes, the next most common causes of acquired sixth nerve palsy in children and young adults include closed head trauma and intracranial neoplasms. Neuroimaging is indicated for acquired sixth nerve palsy if the palsy does not improve rapidly or if other neurological signs are present. Other causes of an acquired sixth nerve palsy include Gradenigo’s syndrome (mastoiditis and sixth nerve palsy), meningitis, myasthenia gravis, and cavernous sinus disease.

Sixth nerve palsy is typically associated with limited abduction and an esotropia that increases upon gaze to the side of the palsy (Fig. 10-10). On attempted abduction, there is relative lid fissure widening because both the medial and lateral rectus muscles are relaxed on attempted adduction and the posterior orbital pressure proptoses the eye. Remember that, on attempted abduction, the medial rectus muscle is inhibited (Sherrington’s law). Mild sixth nerve paresis may allow relatively good lateral rectus function and show only a trace limitation of abduction. These patients, however, will have a pattern of divergence paresis with an esotropia that is greater in the distance than at near. The divergence paresis pattern should alert the examiner to the possibility of a sixth nerve paresis.

Initial therapy of a traumatic or vascular sixth nerve palsy is observation for 6 months while monitoring the patient for spontaneous recovery. Spontaneous recovery of traumatic sixth

A

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FIGURE 10-10A,B. (A) Photographs of a child with a traumatic right sixth nerve palsy and poor lateral rectus function, evidenced by absent abduction saccades and severe limitation of abduction of the right eye. There is 4 limitation of abduction as the right eye does not go past midline.

(B) Results after surgery consisting of a right Hummelsheim transposition and a right medial rectus recession of 6.0 mm. Note the eyes are orthotropic in primary position. There is improved abduction, but abduction remains limited.

nerve palsy is approximately 80% for unilateral cases and 40% for bilateral cases.53 A complete palsy at the initial presentation and bilateral involvement indicate a poor prognosis for recovery.52 During the observation period, alternate monocular occlusion or press-on prisms can be used to eliminate diplopia if a face turn does not allow fusion. To prevent secondary contracture of the medial rectus muscle and increase the chances for recovery, some advocate the use of botulinum injection into the ipsilateral medial rectus muscle.10,74 Botulinum paralyzes the muscle for 3 to 6 months, thus preventing contracture. The hope is that preventing secondary contracture of the medial rectus muscle will increase the chances of recovery without strabismus surgery. The use of botulinum remains controversial, however. Studies comparing botulinum to conservative treatment for the management of nerve palsy have shown no significant difference in recovery rates.53,65 Holmes et al., in a prospective multicenter study of acute traumatic sixth nerve palsy or paresis, reported that patients treated either with botulinum or conservatively had similarly high recovery rates.53 It should be noted that, after a botulinum injection into the medial rectus muscle for a complete sixth nerve palsy, both the medial and lateral rectus will be paralyzed, resulting in essentially no horizontal movement of the paretic eye. Therefore, the patient

should be warned that the paretic eye may have decreased movement after the injection. In addition, the surgeon should be aware that the effects of botulinum can last more than 6 months, and surgery should be delayed until the botulinum has dissipated.

After the 6-month observation period, lateral rectus muscle function should be evaluated, as this is critical for determining the surgical plan. Lateral rectus muscle function can be assessed by saccadic velocity testing and the active forced-generation test. If the saccadic velocities are less than 60% of normal or the active forced-generation test is estimated to be half of the normal fellow eye, a vertical rectus muscle transposition procedure is indicated.

Transposition procedures act by moving innervated vertical rectus muscles to the lateral rectus insertion to provide lateral force. The lateral force of the transposition does not appropriately activate on attempted abduction but, instead, provides a constant lateral force. Transposition of vertical rectus muscles can involve the full muscle (full-tendon transfer) or the muscle can be split longitudinally and only half the muscle is transferred (partial-tendon transfer). In addition to a transposition, patients with significant residual paresis almost always require an ipsilateral medial rectus recession to reduce adduction forces.

The vertical rectus muscles provide substantial circulation to the anterior segment. Older adult patients, especially those with arteriosclerotic disease or hyperviscosity syndromes, are at risk for developing anterior segment ischemia after vertical recti transposition, particularly those receiving full-tendon transfers. A partial-tendon transfer procedure should be considered in these patients to maintain anterior circulation and prevent anterior segment ischemia. Modifications of the Hummelsheim partial-tendon transposition include suturing the transposed vertical muscle to the lateral and resecting a few millimeters of the transposed vertical muscle halves.18,82 An important aspect of the partial-tendon transfer is to fully mobilize the muscle being transferred by splitting the vertical rectus muscles for at least 14 mm posterior to their insertions.135 If carefully performed, a partial-tendon transfer procedure results in long-term good postoperative eye alignment while reducing the risk of anterior segment ischemia. Other options include full-tendon transposition with injection of botulinum toxin to the medial rectus

Duane’s cocontraction syndrome. Cocontraction of the lateral rectus muscle against the medial rectus muscle on adduction causes globe retraction, producing relative enophthalmos and lid fissure narrowing.94 There are various patterns of innervation that account for the four types of Duane’s syndrome. Figure 10-11 shows a diagram of various patterns of abnormal innervation possible in DRS.

Table 10-6 explains the various types of DRS as they correlate to the innervation patterns noted in Figure 10-11. In Duane’s type I, there is agenesis of the sixth nerve and the sixth nerve nucleus, with part of the medial rectus branch of the third nerve going to the lateral rectus muscle. Because most of the medial rectus branch of the third nerve appropriately goes to the medial rectus muscle, the eye will adduct with cocontraction by the aberrantly innervated lateral rectus muscle. This contraction causes lid fissure narrowing; however, because of the absent

A B C D

FIGURE 10-11A–D. Diagrammatic representation of misdirection of nerve fibers in Duane’s syndrome. The aberrant nerve pathway is shown in red, and the dotted lines represent nerve hypoplasia or agenesis. (A) type I: poor abduction and good adduction. Agenesis of the sixth nerve and part of the third nerve splits to innervate both the medial and the lateral rectus muscles, but most of the medial rectus nerve goes to the medial rectus muscle so adduction is intact. (B) Type II: poor adduction and good abduction. Sixth nerve is intact and innervates the lateral rectus muscle, but the medial rectus nerve splits to innervate the medial and lateral rectus muscles. There is poor adduction because the lateral rectus contracts against the medial rectus muscle. (C) Type III: poor adduction and poor abduction. Agenesis of the sixth nerve and part of the third nerve splits to innervate both the medial and the lateral rectus muscles. The split is equal so the eye does not move in or out. (D) Synergistic divergence and paradoxical abduction on attempted adduction. Agenesis of the sixth nerve and part of the third nerve splits to innervate both the medial and the lateral rectus muscles, but most of the medial rectus innervation goes to the lateral rectus muscle. When the eye attempts to adduct, it abducts because the medial rectus nerve innervates the lateral rectus muscle.

TABLE 10-6. Classification of Duane’s Syndrome.

Type I Duane’s: most common

Poor abduction and good adduction. The medial rectus muscle receives most of the medial rectus nerve innervation and the lateral rectus receives minimal innervation from the medial rectus nerve, with agenesis of the sixth nerve. Because the medial rectus receives most of the innervation, the Duane’s eye is usually fixed in an adducted position with an esotropia in primary position, and there is a compensatory face turn in the direction of the Duane’s eye (i.e., left face turn for a left Duane’s type I).

Type II Duane’s: least common, extremely rare

Poor adduction and good abduction. EMG recordings show the lateral rectus muscle to contract appropriately on abduction, but it also contracts paradoxically on adduction; this probably represents a partial innervation of the lateral muscle by the sixth nerve nucleus (as purposeful abduction is present), plus splitting of the medial rectus nerve to innervate the medial and lateral rectus muscles.

Type III Duane’s: second most common

Poor adduction and poor abduction (the eye has little horizontal movement). Equal innervation of the medial and lateral rectus muscles by the medial rectus nerve, with congenital absence of the sixth nerve. Because the medial and lateral forces are similar, the eye will rest in approximately primary position and there will be no significant face turn. In some cases, an exotropia is present in primary position because the lateral rectus receives slightly more innervation than the medial rectus muscle; this causes a face turn away from the Duane’s eye.

Synergistic divergence: extremely rare

Paradoxical abduction on attempted adduction and poor abduction. Little or no innervation of the lateral rectus by the sixth nerve. Most of the medial rectus nerve goes to the lateral rectus muscle. On attempted adduction, the lateral rectus is stimulated by the medial rectus nerve and the eye paradoxically abducts.

sixth nerve, there is no abduction (Fig. 10-12). If the medial rectus nerve equally innervates the medial and lateral rectus muscles, then the cocontraction of the lateral rectus muscle will equal the appropriate contraction of the medial rectus muscle, and the eye will have limited adduction in addition to limited abduction because of the sixth nerve agenesis. This pattern of poor adduction and abduction is typical of Duane’s type III (Fig. 10-13). In the rare Duane’s type II syndrome, abduction is intact but is limited because part of the sixth nerve innervates the lateral rectus muscle and part of the medial rectus nerve innervates the lateral rectus muscle. Another rare form of Duane’s syndrome is synergistic divergence. In this syndrome, most of the third nerve that should innervate the medial rectus muscle aberrantly innervates the lateral rectus muscle, causing the Duane’s eye to paradoxically abduct on attempted adduction.124

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FIGURE 10-14A,B. Photographs of an upshoot (A) and downshoot (B), right eye, occurring on attempted adduction associated with Duane’s syndrome of right eye.

tion, and (4) significant upshoot or downshoot. Usually, surgery is electively performed around age 3 to 8 years, as these patients have excellent fusion and the condition is stable. Rarely will a DRS patient have amblyopia and, when present, it is almost always associated with anisometropia. Amblyopia should be

the first priority in these unusual cases. In general, muscle resections should be avoided in DRS, because resections can make the cocontraction and lid fissure narrowing worse.

SURGERY FOR DRS TYPE I WITH ESOTROPIA AND IPSILATERAL FACE TURN

In cases with esotropia and Duane’s type I, the Duane’s eye is in an adducted position and there is a face turn toward the Duane’s eye. The medial rectus muscle is usually contracted and tight. The simplest, most effective treatment for Duane’s type I with esotropia is an ipsilateral medial rectus recession (between 5.0 and 7 mm). In adult patients, place the medial rectus muscle on an adjustable suture and adjust to a 5° to 10° overcorrection so there is a small exotropia in primary position; this results in stable long-term correction of the face turn. Remember, the lateral rectus muscle is not denervated, as in the case of a sixth nerve palsy, but has innervation provided by part of the medial rectus nerve. This tonic innervation provides stabilizing abduction force, so a muscle transposition procedure is not required. Some have advocated a transposition of the vertical rectus muscles laterally for DRS and esotropia. This procedure is more invasive and has the risk of producing anterior segment ischemia. The transposition procedure also has a risk of inducing a vertical deviation in approximately 15% of patients. This author prefers the simple and effective ipsilateral medial rectus recession for Duane’s type I with esotropia.

SURGERY FOR DRS TYPE III WITH EXOTROPIA AND CONTRALATERAL FACE TURN

In a patient with Duane’s and exotropia, it is almost always a Duane’s type III. The eye is resting in abduction, and the face turn is away from the Duane’s eye. There is usually a tight lateral rectus muscle, and these patients require an ipsilateral lateral rectus recession. If there is an upshoot or downshoot associated with the Duane’s type III, then consider a Y-split procedure with the lateral rectus recession.

TREATMENT OF GLOBE RETRACTION

Globe retraction can be diminished by recessing both the ipsilateral medial rectus and lateral rectus muscles. In patients with esotropic DRS and severe globe retraction, add a lateral rectus recession, but recess the medial rectus muscle more than the lateral rectus to compensate for the esotropia. In exotropic DRS,