2.Deviations can be caused by innervational disorders (overaction or underaction of muscles) or mechanical problems (bone, muscle, or soft-tissue abnormalities within the orbit).
3.Whether it is an innervational or mechanical problem, one of the most common causes of a true vertical tropia is fourth nerve (superior oblique) palsy. Thus, the clinical examination must rule out this possibility.
4.If the deviation is incomitant in the horizontal plane or is long-standing and comitant, a head-tilt test (see Chapter 7, Fig 7-10) should be performed to determine whether an oblique muscle palsy may be the cause.
5.In a case of superior oblique palsy, the clinician must assume the palsy is bilateral until it is proven otherwise, especially when the patient has a history of trauma or a lesion of the central nervous system.
Incomitant Vertical Tropias
Incomitant vertical tropias commonly feature a hypertropia that is significantly worse on gaze to one side. They are often, but not exclusively, associated with oblique muscle abnormalities.
Overelevation and Overdepression in Adduction
There are several causes of overelevation in adduction (OEAd) and overdepression in adduction (ODAd) (Tables 11-1, 11-2). These include true overaction and underaction of the oblique muscles (see later in this chapter), as well as several conditions that can simulate oblique muscle overactions. These cases have also been labeled oblique muscle pseudo-overactions.
Table 11-1
Table 11-2
DVD can lead to an overelevation in adduction when the line of sight of the involved eye is blocked by the nose. There are circumstances, such as with large-angle exotropia and thyroid eye disease, in which clinical examination of ocular rotations indicates apparent overaction of both the superior and the inferior oblique muscles. In such cases, elevation or depression of the vertical rectus muscle of the opposite, abducting eye is restricted in the lateral portion of the bony orbit. The clinical findings can be explained as an attempt by the vertical rectus muscle to overcome this restriction through extra innervation, which, according to Hering’s law (see Chapter 5), is distributed to the yoke oblique muscle as well. Alternatively, overelevation may be due to slippage of a tight lateral rectus as the eye adducts and rises above or below the midline (see Chapter 10). Unless it is severe, this condition does not require that the surgical plan include weakening of the oblique muscle.
What appears to be an overaction may actually be due to abnormal function of a different extraocular muscle. Magnetic resonance imaging (MRI) studies have found connective tissue pulleys where the path of the inferior oblique muscle crosses that of the inferior rectus muscle. This arrangement is said to lead to a dynamic interaction of these muscles during vertical rotation that could give the appearance of overaction (see Chapter 3). In addition, malpositioning of the vertical rectus pulleys can lead to anomalous vertical actions that can simulate oblique muscle overactions. This can be seen in craniofacial syndromes. For example, an inferiorly displaced lateral rectus muscle can cause the normally positioned medial rectus muscle to act as an elevator in adduction; this causes an overelevation in adduction and a V-pattern deviation that simulate an inferior oblique muscle overaction. Conversely, a superiorly displaced lateral rectus muscle can produce an overdepression in adduction—simulating a superior oblique overaction—along with an A-pattern deviation. Lateral and medial malpositioning of vertical rectus muscles can also create pseudooveractions of oblique muscles. One treatment implication is that large A and V patterns associated with these anomalous pulley positions respond poorly to oblique muscle surgery; it is more effective to relocate rectus muscle positions.
Other causes of OEAd and ODAd include the upshoots and downshoots of Duane retraction syndrome (see Chapter 12), restrictions of the superior or inferior rectus muscles (causing overinnervation of contralateral oblique muscles), skew deviation (see BCSC Section 5, NeuroOphthalmology), limitation of elevation in abduction after inferior oblique muscle anterior transposition (anti-elevation syndrome; see Chapter 14), and severe Brown syndrome (see Chapter 12).
Inferior oblique muscle overaction
Overaction of the inferior oblique muscle is one cause of OEAd. It is termed primary when it is not associated with superior oblique muscle palsy. It is called secondary when it accompanies palsy of the superior oblique muscle or the contralateral superior rectus muscle. The eye is elevated in adduction, both on horizontal movement and in upgaze (Fig 11-1).
Figure 11-1 Bilateral inferior oblique muscle overaction. Overelevation in adduction, seen best in the upper fields. (Courtesy of
Edward L. Raab, MD.)
One explanation of primary overaction relates to vestibular factors governing postural tonus of the extraocular muscles. Some observers have questioned the possibility of a true primary inferior oblique overaction, preferring to describe the movement merely as overelevation in adduction.
Clinical features Primary inferior oblique muscle overaction has been reported to develop between ages 1 and 6 years in up to two-thirds of patients with infantile strabismus (esotropia or exotropia). It also occurs, less frequently, in association with acquired esotropia or exotropia and, occasionally, in
patients with no other strabismus. Bilateral overaction can be asymmetric; this is usually seen when vision is poor in 1 eye, leading to greater overaction in that eye.
With the eyes in lateral gaze, alternate cover testing shows that the higher (adducting) eye refixates with a downward movement and that the lower (abducting) eye refixates with an upward movement. When inferior oblique muscle overaction is bilateral, the higher and lower eyes reverse their direction of movement in the opposite lateral gaze. These features differentiate inferior oblique overaction from DVD (see discussion later in this chapter), in which neither eye refixates with an upward movement, whether adducted, abducted, or in primary position. A V-pattern horizontal deviation (see Chapter 10) and extorsion are common with overacting inferior oblique muscles.
Management In all but the mildest cases, a procedure to weaken the inferior oblique muscle (recession, disinsertion, myectomy, marginal myotomy, or anterior transposition) is indicated. Some surgeons grade the weakening procedure depending on the severity of the overaction (see also Chapter 14). Variations in the structure or path of this muscle may affect the surgical result.
Some observers believe that a modest recession actually functions as an anterior transposition, an operation that is useful for correcting marked overaction of the inferior oblique muscle and DVD— particularly when both are present simultaneously. Extorsion can also be improved by this procedure. Results vary according to the new location of the anterior and posterior fibers of the reinserted inferior oblique muscle. A spread-out reinsertion, especially if closer to the limbus than the inferior rectus muscle, can restrict elevation, especially when the eye is abducted (anti-elevation syndrome). In general, weakening of the inferior oblique muscles has an insignificant effect on horizontal alignment in primary position.
Kushner BJ. Restriction of elevation in abduction after inferior oblique anteriorization. J AAPOS. 1997;1(1):55–62.
Superior oblique muscle overaction
Superior oblique muscle overaction is one of several causes of overdepression in adduction (ODAd).
Clinical features A vertical deviation in primary position often occurs with unilateral or asymmetric bilateral overaction of the superior oblique muscles. The lower eye contains the overacting superior oblique muscle in unilateral overaction and the more prominently overacting superior oblique muscle in bilateral overaction. The overacting superior oblique muscle causes a hypotropia of the adducting eye, which is accentuated in the lower field (Fig 11-2). A horizontal deviation, most often exotropia, may be present and may lead to an A pattern (see Chapter 10). Intorsion is common with superior oblique muscle overaction. Most cases of bilateral superior oblique overaction are primary overactions.
Figure 11-2 Top row, Bilateral superior oblique muscle overaction. Overdepression in adduction, seen best in the lower fields. Bottom row, Associated bilateral inferior oblique muscle underaction. (Courtesy of Edward L. Raab, MD.)
Management In a patient with a clinically significant hypertropia or hypotropia or an A pattern, a procedure to weaken the superior oblique tendon (recession, tenotomy, tenectomy, or lengthening by insertion of a silicone spacer or nonabsorbable suture or by Z-lengthening) is appropriate (see Chapter 14). Significant intorsion will also be reduced with any of these procedures. Many surgeons are reluctant to perform superior oblique tendon weakening in patients with single binocular vision because the resulting, sometimes asymmetric, torsional and/or vertical effects can cause diplopia in these patients. As with inferior oblique muscle overaction, the horizontal deviation can be corrected during the same operative session. Some surgeons, anticipating a convergent effect in primary position, adjust their surgical amounts for horizontal rectus muscles when simultaneously weakening the superior oblique muscles.
Superior Oblique Muscle Palsy
The most common paralysis of a single cyclovertical muscle is fourth nerve palsy, which involves the superior oblique muscle. It can be congenital or acquired; if the latter, it is usually a result of closed head trauma or, less commonly, vascular problems of the central nervous system, diabetes mellitus, or a brain tumor. Direct trauma to the tendon or the trochlear area is an occasional cause of unilateral superior oblique muscle palsy. One study showed that most patients with congenital superior oblique palsy had absent ipsilateral trochlear nerves and varying degrees of superior oblique muscle hypoplasia, while a minority had normal nerves and muscle bulks.
The same clinical features can result from a congenitally lax, attenuated, or even absent superior oblique tendon; from an unusual course of the muscle; or from functional consequences of malpositioned orbital pulleys—although strictly speaking, these are not paralytic entities. Superior oblique muscle underaction can also occur in several craniofacial abnormalities (see Chapter 18).
To differentiate congenital from acquired superior oblique muscle palsy, the clinician can examine childhood photographs to detect a compensatory head tilt. Facial asymmetry from long-standing head tilting and large vertical fusional amplitudes also indicate chronicity. The distinction is important
because recently diagnosed palsy that cannot be attributed to known trauma suggests the possibility of a serious intracranial lesion and the need for neurologic investigation. Diagnostic evaluation for isolated nontraumatic fourth nerve palsy usually uncovers ischemic or idiopathic etiologies. Lack of signs of recovery by 3 months after onset should prompt neuroimaging. It should be noted that congenital superior oblique muscle palsy may not manifest until the child is older, but a large vertical fusional amplitude is typically present with no associated neurologic disorders. In this case, neuroimaging may not be necessary.
Neurologic aspects of superior oblique muscle palsy are discussed in BCSC Section 5, NeuroOphthalmology.
Yang HK, Kim JH, Hwang JM. Congenital superior oblique palsy and trochlear nerve absence: a clinical and radiological study. Ophthalmology. 2012;119(1):170–177. Epub 2011 Sep 15.
Clinical features
Either the normal or the affected eye can be preferred for fixation. Examination of versions usually reveals underaction of the involved superior oblique muscle and overaction of its antagonist inferior oblique muscle; however, the action of the superior oblique muscle can appear normal. In a unilateral palsy, the hyperdeviation is typically incomitant, especially in the acute stages. Over time, contracture of the ipsilateral superior rectus or contralateral inferior rectus muscle can lead to a “spread of comitance,” with the result that there is minimal difference in the magnitude of the hypertropia when the patient looks from one side to the other. If depression cannot be evaluated because of the eye’s inability to adduct (eg, in third nerve palsy), superior oblique muscle function can be evaluated by observing whether the eye intorts, as judged by the movement of surface landmarks or examination of the fundus, when the patient attempts to look downward and inward from primary position. Loss of strength of the superior oblique muscle leads to extorsion of the eye. If the degree of extorsion is large enough, subjective incyclodiplopia, in which the patient describes the image as appearing to tilt inward, can occur.
The diagnosis of unilateral superior oblique muscle palsy is further established by results of the 3- step test (Fig 11-3; see also Chapter 7, Fig 7-10) and the double Maddox rod test to measure torsional imbalance (see Chapter 7). However, the results of the 3-step test can be confounded by DVD, entities involving restriction, and some cases of skew deviation. During the double Maddox rod test or ophthalmoscopy, intorsion of the higher eye—instead of the expected extorsion—signifies skew deviation, especially when there are associated neurologic findings. In addition, if the patient is placed supine, the vertical tropia typically does not change in superior oblique palsy, while it decreases significantly in skew deviation. Some ophthalmologists document serial changes in the deviation by means of the Hess screen or the Lancaster red-green test or by plotting the field of single binocular vision (see Chapter 7).
Figure 11-3 Right superior oblique muscle palsy. There is a right hypertropia in primary position that increases in left gaze and with head tilt to the right. Note accompanying overaction of the right inferior oblique muscle. (Courtesy of Edward L. Raab, MD.)
To differentiate bilateral from unilateral superior oblique muscle palsy, the following criteria are used:
Unilateral cases usually show little if any V pattern (see Chapter 10) and less than 10° of extorsion in downgaze. Subjective incyclodiplopia is uncommon, unless the palsy is severe. The 3-step test yields positive results for the involved side only. Abnormal head positions—usually a tilt toward the shoulder opposite the side of the weakness—are common. Finally, the oblique muscle dysfunction is confined to the involved eye.
Bilateral cases usually show a V pattern. Extorsion is 10° or more in downgaze; more than 20° of extorsion is highly suggestive of bilateral involvement. Subjective incyclodiplopia is common in acquired bilateral cases. The Bielschowsky head-tilt test yields positive results on tilt to each side—that is, right head tilt reveals a right hypertropia and left head tilt a left hypertropia. There is bilateral oblique muscle dysfunction. Patients may exhibit a chin-down head posture. Markedly asymmetric bilateral palsies that initially appear to be unilateral are called masked bilateral palsies. Signs of masked bilateral palsy include bilateral objective fundus extorsion, esotropia in downgaze, and even the mildest degree of oblique muscle dysfunction on the presumedly uninvolved side. Masked bilateral palsies are more common in patients with closed
head trauma. They must be distinguished from situations in which the initial palsy is overcorrected, leading to a postoperative oblique muscle abnormality in the fellow eye.
Management
In small, symptomatic deviations that lack a prominent torsional component—especially those that have become comitant—prisms that compensate for the hyperdeviation in primary position may be used to overcome diplopia. Abnormal head position, significant vertical deviation, diplopia, and asthenopia are indications for surgery. Common operative strategies are discussed in the following sections (see also Chapter 14).
Unilateral superior oblique muscle palsy The approach to surgical treatment of a unilateral palsy depends on several factors:
comitance or incomitance of the hyperdeviation size of the hyperdeviation in primary position
diagnostic gaze positions in which the hyperdeviation is largest presence of cyclodiplopia or significant extorsion
degree of laxity of the superior oblique tendon
When the deviation is incomitant, the surgeon can weaken the antagonist inferior oblique muscle if the hyperdeviation is worse in contralateral upgaze or strengthen the weak superior oblique muscle if the hyperdeviation is worse in contralateral downgaze. If the superior oblique muscle is lax, as in some cases of congenital superior oblique palsy, the tendon should be tightened; the most common procedure choice is tendon tucking. Laxity can be confirmed at surgery by a forced-duction test in which the globe is pushed (translated) posteriorly into the orbit while it is simultaneously extorted, thus tensing the superior oblique tendon. The presence of cyclodiplopia or significant extorsion also indicates that a superior oblique tendon strengthening procedure should be considered for inclusion in the surgical plan; options include tendon tucking and the various forms of the Harada-Ito procedure (see Chapter 14).
If the deviation is no greater than 15Δ in primary position, one of these options alone may be effective. When the inferior oblique muscle is weakened, the amount of deviation in primary position that is corrected by any weakening technique is proportional to the degree of preoperative overaction of the muscle. This procedure is not performed in skew deviation because inferior oblique muscle weakening would aggravate the intorsion of the higher eye.
If the hyperdeviation is incomitant and measures greater than 15Δ in primary position, it usually is also large in the ipsilateral (secondary) gaze field. In this situation, recession of the ipsilateral superior rectus muscle or the contralateral (yoke) inferior rectus muscle should be added to the oblique muscle surgery. The choice depends on whether the hyperdeviation is worse in downgaze or upgaze, as well as the tightness of these muscles on forced-duction testing. Either muscle can be recessed with an adjustable suture.
If the deviation has become comitant, vertical rectus muscle surgery is generally preferred. For deviations of less than 15Δ–20Δ, recession of 1 vertical rectus muscle should suffice; for larger hyperdeviations, both may have to be weakened.
In the unusually severe case with a vertical deviation greater than 35Δ in primary position, 3- muscle surgery is usually required. In this situation, most surgeons favor recession of the overacting antagonist inferior oblique muscle, plus either the ipsilateral superior rectus or contralateral inferior rectus muscle or both, as dictated by forced-duction test results. Ipsilateral superior oblique tendon tucking may have to be included if the tendon is lax.