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

recess the lateral rectus more than the medial rectus muscle or, for a large exotropia, recess only the lateral rectus muscle (large recession). For orthotropic DRS without a face turn, recess the medial and lateral rectus muscles the same amount.

TREATMENT OF UPSHOOT AND DOWNSHOOT

Two approaches to reduce upshoot and downshoot associated with DRS include these:

1.Y-splitting with recession of the lateral rectus muscle

2.Posterior fixation suture (Faden) of the lateral rectus and appropriate recession of horizontal recti

The Y-splitting procedure of the lateral rectus muscle works by placing some of the lateral rectus muscle above and below the horizontal midline, thus preventing an upshoot or downshoot when the eye is in adduction.95,100 By combining a recession of the lateral rectus muscle with the Y-split, one can treat both an exotropia Duane’s type III with an upshoot and downshoot. In patients with orthotropic DRS and a severe upshoot and downshoot, recess the ipsilateral medial rectus muscle along with a recession and Y-split of the ipsilateral lateral rectus muscle. The posterior fixation suture acts to stop slippage of the lateral rectus muscle when the eye rotates up or down, and a concurrent recession reduces cocontraction. The authors have found the Y- splitting procedure is more effective than the posterior fixation suture.

Fourth Nerve Palsy (Superior Oblique Palsy)

See Chapter 9.

Third Nerve Palsy

Third nerve palsy involves all the extraocular muscles except the lateral rectus and the superior oblique. The strabismus is characterized by the eye being “down and out” with a small hypotropia and a large exotropia (Fig. 10-15). There is limited depression, elevation, and adduction, along with preservation of abduction (intact innervation lateral rectus muscle) and intorsion seen on attempted eye movement down and in (intact innervation superior oblique muscle). Ptosis, pupillary dilatation, and hypoaccommodation are also present in a complete third nerve palsy. A congenital third nerve paresis is often

FIGURE 10-15. Photograph of a left third nerve palsy; there is a left ptosis and the left eye is “down and out” (left exotropia and hypotropia).

partial, without ptosis, with variable amounts of limited elevation, depression, and adduction, with pupillary sparing, and may show oculomotor synkinesis.

The two most common causes of pediatric third nerve palsy are idiopathic congenital onset and head trauma. Other causes include migraine, an association with a viral syndrome, an intracranial tumor, or, rarely, a posterior communicating aneurysm.14,62,105 Nontraumatic acquired third nerve palsy cases must undergo a full workup with neuroimaging.62

TREATMENT

The treatment of complete third nerve palsy is extremely difficult because there are no vertical muscle forces to move nasally, as all the vertical recti are paretic. Superior oblique tendon transfer to the medial rectus insertion has been suggested as a way of providing medial forces.104 This procedure, however, does not increase adduction as it only creates a leash and limits depression of the eye, resulting in a large hypertropia in downgaze. An ipsilateral superior oblique tenotomy, with ipsilateral recession of the lateral rectus and a large resection of medial rectus, is probably the procedure most often used for a third nerve paresis with an exotropia and hypotropia and some medial rectus function. In cases where this procedure has failed to correct the

exotropia, this author has split the lateral rectus and transposed the halves to the nasal border of the superior and inferior rectus muscles. This procedure has worked in centering the eye; however, horizontal excursions are minimal.

In addition to the difficulty in treating the strabismus, patients with a third nerve palsy and ptosis with poor or absent levator function, are at risk for developing corneal exposure if the ptosis is repaired. Ptosis should be managed with a silicone frontalis sling procedure, aiming for intentional undercorrection of the lid position if there is a poor Bell’s phenomenon. The silicone sling procedure has an advantage of being reversible if corneal exposure becomes a problem. Patients should be warned about the risk of corneal exposure and that their diplopia may be worse after lifting the eyelid, as this removes the occlusion. Many wise patients and physicians opt for leaving the ptosis alone if associated with a poor superior rectus muscle function evidenced by a poor Bell’s phenomenon.

Inferior Oblique Paresis

See Chapter 9.

Möbius Syndrome

Möbius syndrome is characterized by a combination of facial palsy, sixth nerve palsy, partial third nerve palsy, and distal limb abnormalities such as syndactyly, club foot, or even amputation defects.23 There is some degree of intellectual impairment in 75% of patients.23,131 The Möbius infant typically presents with esotropia, limited abduction, lack of facial expression, and difficulty feeding caused by a poor sucking reflex. Craniofacial anomalies can occur and include micrognathia, tongue abnormalities, and facial or oral clefts. Ocular motility abnormalities include limited abduction in more than 90% of cases and limited adduction in 65% of cases.23,66,86 Some patients have globe retraction on adduction and failure to abduct, typical of Duane’s syndrome. The inheritance pattern of Möbius syndrome is usually sporadic, and there is great variability of findings,44 suggesting that the syndrome represents a heterogeneous group of neuromuscular disorders.87 Prenatal exposure to misoprostol, the abortion-inducing drug, has been implicated as a risk factor.23,41,120 Treatment of the strabismus is tailored to the individual situation. Patients with a large esotropia, tight medial rectus

muscles, and poor abduction are probably best treated with large bilateral medial rectus recessions similar to the treatment of a patient with congenital fibrosis syndrome.

Sinus Surgery and Medial Rectus Muscle Injury

Endoscopic sinus surgery can result in severe damage to the medial rectus muscle and even visual loss.31,69,98 This damage occurs when the thin ethmoid bone is violated during endoscopic sinus surgery and the medial rectus muscle is traumatized. In most cases, part of the medial rectus muscle is removed, often in the area of the neuromuscular junction (two-thirds of the way back from the insertion or approximately 25 mm posterior to the insertion). On MRI, the medial rectus may be seen to be myectomized and pulled into the ethmoid sinus (Fig. 10-16). The inferior rectus and inferior oblique muscles can also be traumatized, but this is less common.98 Treatment of the adduction deficit and exotropia depends on the extent of the damage to the medial rectus muscle and the state of the innervation.119 Unfortunately, in most cases, there is poor medial rectus muscle function secondary to neuromuscular junction injury or a posterior myectomy. If medial rectus muscle function is poor, a partial-tendon transfer of the vertical rectus muscle to the medial rectus insertion (Hummelsheim) or a procedure to create a nasal tether to pull the eye to midline is indicated.6 Standard exploration and muscle retrieval techniques (used for locating lost muscles) do not work if the injury involves the neuromuscular junction or if a posterior myectomy was performed.

Aplasia of Extraocular Muscles

Although virtually all extraocular muscles have been described as being congenitally absent, the inferior rectus is most commonly affected.13,70,101 The condition is often associated with craniofacial dysostosis, anencephaly, or other congenital head anomalies.8,22,42,88,113 Aplasia of the inferior rectus, superior rectus, and superior oblique muscles can occur in otherwise healthy children without craniofacial abnormalities.27,58,67 Figure 10-17 depicts a case in which this author surgically explored to find aplasia of the right inferior rectus and hypoplasia of the left inferior rectus muscle. This child was healthy and presented with a right hypertropia and bilateral limited depression, right eye more than left eye. An absent rectus muscle is managed by

DISSOCIATED VERTICAL DEVIATION AND DISSOCIATED HORIZONTAL DEVIATION

Dissociated vertical deviation (DVD) is the tendency for an eye to elevate, abduct, and extort, when binocularity is suspended by occlusion or the patient spontaneously dissociates (often when fatigued). DVD is almost always bilateral, but asymmetrical cases may appear to be unilateral. Prolonged occlusion of the eye that appears not to have DVD, however, will almost always disclose a latent DVD. Note that, with a true hypertropia, there is a corresponding hypotropia of the fellow eye and, on alternate cover testing when the hypertropic eye moves down into primary position, the fellow eye also moves down to become hypotropic. Thus, a true hypertropia is consistent with Hering’s law of yoke muscles. In contrast, DVD violates Hering’s law of yoke muscles because covering the right eye makes the right eye drift up, and covering the left eye makes the left eye drift up with no corresponding hypotropia of the fellow eye (Fig. 10-19). One can think of DVD as two individual hypertropias that are dissociated, thus the term, dissociated vertical deviation. DVD increases on head tilt: head tilt to the right increases a right DVD and head tilt to the left increases a left DVD.

DVD occurs when normal binocular visual development is disrupted and is associated with congenital esotropia, congenital exotropia,11 congenital media opacities (e.g., monocular congenital cataracts), and even unilateral optic nerve hypoplasia. Rarely, this author has seen patients with primary DVD; that is, no horizontal strabismus, and no history of previous strabismus surgery (Fig. 10-19). These patients usually have some degree of stereoacuity, sometimes high-grade stereoacuity.

On version testing, DVD can mimic inferior oblique overaction because the vision of the adducting eye is blocked by the bridge of the nose; this dissociates the eyes, causing the DVD of the adducting eye to be manifest. The two can be distinguished, however, as DVD has no true hypotropia of the opposite eye, and the hyperdeviation is the same in abduction as in adduction. With inferior oblique overaction, there is a hypotropia of the opposite eye and the deviation increases as the eye moves into adduction. DVD and inferior oblique overaction often coexist with congenital esotropia.127

The cause of dissociated vertical deviation is unknown. Guyton hypothesized that abnormal binocular development causes unbalanced input to the vestibular system, resulting in