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

latent nystagmus with a cyclovertical movement. Cycloversion/ vertical vergence is invoked to damp the cyclovertical nystagmus (a cyclovertical “nystagmus blockage” phenomenon), aiding vision in the fixing eye. Unfortunately, this mechanism also produces unavoidable and undesirable elevation and extorsion of the fellow eye that results in DVD.45

This author has a theory about the neurophysiological basis for DVD. It is interesting that DVD is associated with disruption of early binocular visual development. The interstitial nucleus of Cajal is a brainstem nucleus that regulates cyclovertical movements. The interstitial nucleus of Cajal receives inhibitory input from binocular cells in the occipital cortex, and these inhibitory pathways act to control this nucleus. Lesions around the interstitial nucleus of Cajal that interrupt the binocular inhibitory input result in nucleus disinhibition, which is clinically manifested as seesaw nystagmus. Seesaw nystagmus is a dissociated cyclovertical/horizontal nystagmus. When seesaw nystagmus occurs in infancy, it can look quite similar to DVD. Infantile strabismus or a dense monocular congenital cataract disrupts binocular visual development and reduces binocular cortical cells. Perhaps the lack of binocular cortical cells associated with congenital strabismus or a unilateral blurred retinal image in infancy, results in reduced binocular inhibitory input to the interstitial nucleus of Cajal or similar cyclovertical brainstem nuclei. Reduced binocular inhibitory input would cause disinhibition of these cyclovertical nuclei, giving rise to what we see clinically as DVD.

If early surgery for infantile esotropia improves binocularity, then children who have had early surgery should have less DVD. Recent reports on the incidence of DVD in children who have had early surgery for infantile esotropia, however, remain unchanged from reports 30 years previous.81,136 Even though the incidence may be the same, the severity of DVD seems to have diminished over the past few decades. It is this author’s opinion, along with the observations of senior expert strabismologists, that the incidence of severe DVD requiring surgery has decreased. Performing surgery for a large, cosmetically obvious DVD in the 1970s and early 1980s was commonplace. As a resident in ophthalmology, this author remembers operating every month on several DVD patients. Over the past several years, there have only been a few cases requiring surgery, and usually on older adults with DVD. The author’s visits to countries where surgeons continue to operate late, after 2 years of age, have disclosed that a very high prevalence of big, surgically

turn. These forms of head posturing can occur independently or in combination, as a patient with a superior oblique palsy will often have both a head tilt and a face turn. Torticollis can be secondary to a musculoskeletal abnormality of the neck or to an ocular problem compensated by head posturing. A simple initial test to determine the cause is to ask the patients to close their eyes and observe for several seconds to see if the head posturing spontaneously improves. If the face turn improves when the eyes are closed, this suggests an ocular cause. Next, passively move the patient’s head from side to side with the patient’s eyes closed. If the range of motion of the head and neck is normal, this verifies that the head posturing is an ocular torticollis; however, a stiff neck indicates a musculoskeletal problem.

By far the most common ocular causes of abnormal head posturing are nystagmus with a null point and incomitant strabismus with compensatory head posturing to allow fusion. A face turn is often identified by observing the patient’s head posture. A better way to evaluate the presence of a face turn is to observe the position of the eyes. Normal patients with straight eyes and no face turn will have both eyes centered within the palpebral fissures. If a face turn is present, there will be a gaze preference with the eyes constantly shifted opposite to the face turn. For example, a face turn to the right is associated with eyes shifted to the left (Fig. 10-20), and a chin elevation will have the eyes shifted down. When examining a patient for a face turn, first observe the position of the eyes and the presence of a gaze preference. Next, turn or tilt the head opposite to the compensatory position to place the eyes into the nonpreferred field of gaze. If there is a face turn to the right, turn the head to the left; if there is a head tilt to the right, tilt the head to the left. While the head is held opposite to the compensatory position, observe for nystagmus or strabismus. If nystagmus occurs or increases with a forced face turn to the opposite side, then a compensatory face turn is present to keep the eyes in the area of the null point. If strabismus is produced by forced head tilt, or turns the eye in with a previously fusing patient, then the compensatory head posturing is adopted to maintain fusion, keeping the eyes in the field of gaze where the eyes are aligned. In addition to face turns and head tilts, chin elevations or depressions can be compensatory for nystagmus or strabismus, and chin elevations compensate for ptosis.

The degree of face turn can be measured by using an orthopedic goniometer placed on the head. Any protractor will work

FIGURE 10-20. Photograph of ocular torticollis in a patient with nystagmus. Patient has a face turn to the right to place the eyes at the null point in leftgaze. The best way to identify a face turn is to evaluate the position of the eyes. If there is a strong gaze preference for an eccentric gaze position, then consider the possibility of a compensatory face turn.

as the line of sight is compared to the direction of the face, with the nose as the pointer.77 An alternative method for measuring face turn associated with Duane’s syndrome or unilateral limited eye movement is to place a prism over the eye with limited rotation, with the apex pointing toward the direction of the deviated eye. The prism is progressively increased until the face turn is corrected. The amount of prism required to neutralize the face turn is recorded in prism diopters. Prism diopters can be converted to degrees by dividing by 2. Prism correction of head posturing can also be used to measure face turns associated with nystagmus.

Incomitant Strabismus Causing Compensatory

Head Posturing

Head posturing compensates for incomitant strabismus by placing the eyes in a field of gaze where the eyes are best aligned to achieve binocular fusion. For example, a patient with a left sixth nerve palsy will have a large esotropia in leftgaze and straight eyes in rightgaze. These patients will adopt a face turn to the left to keep their eyes aligned in rightgaze. An incomitant

strabismus where the eyes are aligned in an eccentric field of gaze can cause an abnormal head posture; this includes cranial nerve palsies, restrictive strabismus, A- or V-patterns, and primary oblique dysfunction. For example, patients with fusion and an A-pattern exotropia or V-pattern esotropia will show a chin depression (eyes straighter in upgaze), whereas an A-pattern esotropia or V-pattern exotropia will show a chin elevation (eyes straighter in downgaze).

The treatment of an abnormal head posture caused by incomitant strabismus is simply to correct the strabismus in primary position and provide a large field of single binocular vision. If the fixing eye has limited ductions, then move the eye with limited movements to primary position, and the normal eye will follow.

Nystagmus Causing Compensatory

Head Posturing

A compensatory head posture can stabilize nystagmus by placing the eyes at the null point. If the null point is to the right, the patient will shift the eyes to the right and have a face turn to the left. Head posturing associated with nystagmus can take the form of a face turn, chin elevation or depression, or a head tilt.

A compensatory face turn associated with congenital nystagmus can be treated using eye muscle surgery to move the eye position from the null point to primary position.77 The general surgical principles for correcting a face turn are as follows5:

1. Kestenbaum–Anderson–Parks (Kestenbaum) procedure: With a compensatory face turn to the right, the eyes will be shifted to the left. Therefore, to correct the face turn, move the eyes to the right into primary position (Fig. 10-21), which is done by moving the right eye out (right medial rectus recession–right lateral rectus resection) and moving the left eye in (left lateral rectus recession and a left medial rectus resection). The amount of surgery for a specific amount of face turn is listed in Table 10-7. Note, Parks Poker Straight 5-6-7-8 (medial recession 5 mm, medial resection 6 mm, lateral recession 7 mm, and lateral resection 8 mm) is a way of remembering the amount of surgery for a small face turn. In most cases, however, larger amounts of surgery are needed.77 Large recessions and resections are needed for a face turn associated with nystagmus. Postoperative

FIGURE 10-21. Drawing showing how to correct a face turn to the right associated with nystagmus using the Kestenbaum procedure. The view is looking down on a face turn to the right with eyes in leftgaze at the null point. Surgically correct the face turn by simply moving the eyes into primary position. The arrows in the diagram indicate moving the eyes to the right to place the eyes in primary position. The left eye is shifted nasally (recess lateral rectus muscle and resect the medial rectus muscle) and the right eye moved temporally (recess medial rectus muscle and resect the lateral rectus muscle) to correct the face turn.

TABLE 16-7. Kestenbaum Procedure for Nystagmus with a Face Turn to the Right (Eyes Shifted Right).

See Figures 10-20, 10-21.

Source: Modified from Refs. 5, 135, permission.

limitation of ocular movements is to be expected, deemed to be an acceptable trade-off.

2. Vertical head posturing: Chin depression (eyes up) is treated with large bilateral superior rectus recessions (8–9 mm) and inferior rectus resections (6–7 mm). For large chin depressions, this can be combined or performed in stages, the superior rectus recessions first, then inferior rectus resections later if necessary. Chin elevations (eyes down) can be treated similarly by recessing the inferior rectus muscles (7–8 mm) and resecting the superior rectus muscles (6–7 mm).99

Surgical therapy should be based on the greatest amount of abnormal head posture measured at distance and near. For example, if the face turn is obvious at distance and not at near, full correction directed at the face turn in the distance should be undertaken. When strabismus coexists with nystagmus, the head posture can be corrected by moving the fixing eye to primary position. Then adjust the fellow eye to compensate for the residual strabismus.

Compensatory head tilts are also associated with nystagmus, which can be corrected by rotating the eyes back to primary position. A head tilt to the right can be treated by surgically extorting the right eye and intorting the left eye.122

SURGICAL TREATMENT OF NYSTAGMUS: NO FACE TURN

Although the Kestenbaum–Anderson–Parks procedure is directed toward eliminating the abnormal horizontal face turn associated with nystagmus, another approach has been described to damp nystagmus in patients without a face turn. Simultaneous retroequatorial recessions of all four horizontal rectus muscles have been reported to decrease the amplitude of nystagmus and improve visual acuity.30,36,97 The precise mechanism responsible for damping the nystagmus is not known, and the long-term effect remains unknown. Vision improves only in cases of motor nystagmus, not in patients with sensory nystagmus who have an abnormal afferent pathway.

Additional Causes of Ocular Torticollis

Less common mechanisms for head posturing do exist. Rarely, a patient with diplopia adopts a head posture that induces maximal image separation rather than fusion, thus making suppression of the diplopic image easier. Other reasons for abnor-

mal head posturing include compensation for visual field defects, restriction of the good eye in monocular patients, manifest latent nystagmus with a face turn to keep the fixing eye in adduction, ptosis with chin elevation, tilting for monocular torsion, and cosmetic reasons. Other causes include asymmetrical dissociated vertical deviation, refractive error in which the patient adopts a face turn presumably to partially block the pupil, inducing a pinhole effect that provides better visual acuity.

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