Treatment

General advice to parents and teachers

Teachers should be instructed to sit the child at the front of the class on the side that allows them to utilize their null zone and to let the child hold reading materials close to his or her face. Parents can be told that, although the nystagmus will persist, children with infantile nystagmus have good vision and do not see the world albinism as moving. In infants with underlying sensory defects (albinism, optic nerve hypoplasia), parents can be told that visual attention may dramatically increase in the sixth month of life. Parents can be assured that the nystag­mus improves considerably over the first five years of life and that optical and surgical treatment may improve it further.

Medical Treatment

Drug therapy for acquired nystagmus has been directed toward augmenting the inhibitory neurotransmitter system (e.g., gamma-amino-butyric acid [GABA]) or inhibiting the excitatory neurotransmitter system (e.g., glutamate).99 Most notably, downbeat nystagmus has been treated successfully with clonazepam (a GABA-ergic inhibitor), and acquired periodic alternating nystagmus has been successfully treated with baclofen (an inhibitor of glutamate release).

In many ways, one-time surgical treatment of infantile nystagmus can be considered a more conservative and economically feasible therapy than life-long medical treatment, especially when the long-term side effects of medications have not been established.

Until recently, the pharmacological treatment of infantile nystagmus has met with limited success. One study noted objective improvement in visual acuity by one or two lines, together with subjective improvement in four of seven infantile nystagmus patients who were treated with baclofen.594 Another study357 purported improved vision in two infantile nystagmus patients with 5-hydroxytryptophan therapy. Given the well-documented visual improvement obtained by optical and surgical treatment of infantile nystagmus, drug therapy has not been included in the therapeutic armamentarium for infantile nystagmus.99 Recently, gabapentin and memantine have been shown to be effective in the treatment of adults with infantile nystagmus.386,498 Neither medication is currently approved for use in children.

Optical Treatment

A recent study by Woo and Bedell588 found that children with infantile nystagmus retain some ability to recognize words outside­ the foveation period. Large size text (i.e., larger than the

level of near acuity would indicate the need for) could therefore serve to improve reading performance by keeping text legible during a larger portion of the infantile nystagmus waveform.588 Correction of significant refractive error in children and adults is the single most powerful therapeutic intervention for improving vision and visual function.279 Sometimes, anomalous head positions are satisfactorily reduced by refractive correction alone.279 The primary optical treatment for infantile nystagmus is glasses. Reinecke467 has stated that fusional convergence damps infantile nystagmus while accommodative convergence does not, so it is advisable to give the full hyperopic refraction. In patients with torticollis, glasses can be prescribed with the optical centers offset to compensate for the eccentric position of gaze. Because infantile nystagmus is damped by physiological convergence, some authors have advocated incorporating base-out prisms into spectacle lenses to increase tonic convergence.389 It is now widely accepted that base-out prisms can be incorporated into spectacle lenses to increase foveation time and to improve vision in infantile nystagmus.155 However, glass prisms are thick and cumbersome, which reduces patient acceptance, especially in children. When prescribing base-out prisms in children, it is usually necessary to incorporate minus-one lenses into the prescription, because the act of converging usually evokes some degree of accommodation. Soft contact lenses offer several advantages over glasses including direct damping of nystagmus, elimination of

peripheral aberrations, and clearer vision in null positions. The value of biofeedback in reducing the intensity of infan-

tile nystagmus and improving vision has been demonstrated in several independent studies.6,16,123,390 Several forms of cutaneous stimulation (including acupuncture) are said to reduce infantile nystagmus.153,301 Dell’Osso and coworkers have also demonstrated that infantile nystagmus is markedly reduced simply by placing contact lenses on the eyes,152,477 as well as by cutaneous stimulation in the dermatome supplied by the ophthalmic division of the trigeminal nerve (i.e., tactile or vibrational stimulus applied to the forehead).153

Surgical Treatment

Strabismus surgery in the treatment of infantile nystagmus falls into two general categories: surgery to treat torticollis and slow to see and take longer acuity.

Surgery to Improve Torticollis

For the most part, treatment of infantile nystagmus has consisted of transferring the null position into primary gaze, thereby eliminating the prominent head turn in some patients with infantile nystagmus.347 This is accomplished by performing a horizontal recess-resect procedure on both eyes (Kestenbaum–Andersen procedure), moving all four

­horizontal rectus muscles to essentially rotate the eyes in the direction of the head turn. The same approaches have been successfully applied to torticollis secondary to acquired nystagmus with oscillopsia.95 For example, a child who assumes a right head turn to maintain the eyes in left gaze is treated with a left lateral rectus recession, left medial rectus resection, right medial rectus recession, and right lateral rectus resection to surgically rotate the eyes conjugately to the right and effectively transfer the null zone to primary gaze.

The Kestenbaum–Anderson procedure both moves and broadens the null zone, causing better foveations in a broader

range of horizontal gaze.141 It thereby improves visual ­function even when an improvement in visual acuity cannot be detected (Fig. 8.10). The field of clear vision in infantile nystagmus can be likened to the field of binocular vision in the patient with strabismus. While the purpose of strabismus surgery is often to expand the field of single binocular vision, the goal of all surgery in infantile nystagmus with torticollis should be viewed as both shifting the null point and expanding the field of clear vision.

Before planning a Kestenbaum–Anderson procedure, it is important to observe the torticollis at distance and near to

rule out a second abnormal head position, which can be worsened by additional surgery. For example, some children manifest a large right head turn when viewing at distance, and a large left head turn when viewing at near. Intermittency of the head turn should not factor into the decision of whether to operate. Head turns are uncomfortable to maintain and chldren who turn their heads to see clearly would do so constantly if they could. As measurements of head turn are notoriously variable in children with congenital nystagmus, the gaze position of minimal nystagmus is a better indicator of null position. In general, the presence of even a small head turn indicates that the horizontal range of good vision is extremely narrow and that gaze acuities and latencies for target recognition must be low in all but a narrow range of horizontal gaze. For this reason, Hertle has recommended performing two muscle recessions with simple tenotomy and reattachment of the other two horizontal muscles for even small head turns (in the range of 10 degrees).276,284 The relative diminution in ocular rotation from two versus four muscle surgery has not been investigated.

The Kestenbaum procedure is most effective when measured gaze-angle nulls are used to determine the amount of eye rotation necessary rather than patient-controlled and inaccurately measured head turns.141,201,202 Reports of “regression” and the need for additional surgeries appear to be due to inadequate initial procedures and not a return of the null angle. Even with “augmented” Kestenbaum–Andersen procedures, late regression continues to be a problem that limits long-term efficacy. Reports touting the efficacy of this procedure should therefore be interpreted with caution in the absence of long-term (several years) follow-up data.

Even when coexistent strabismus is present, the major etiology for anomalous head positions in infantile nystagmus is to adopt a gaze null.278 The coexistence of congenital or manifest latent nystagmus and strabismus can often be managed by surgically moving the fixing eye for the anomalous head posture, combined with moving the nonfixing eye for the resulting strabismus.278 In addition to shifting the null zone, Dell’Osso and Flynn have shown that the Kestenbaum–Anderson procedure expands the null zone and improves visual acuity in some cases.141 Serial ocular motor studies performed by Abadi and Whittle have demonstrated that the final face position following a Kestenbaum procedure does not always correspond precisely to the null zone, suggesting that other unrecognized factors influence the outcome. In our experience, adjustable sutures are contraindicated following a Kestenbaum procedure as the eyes are rotated to one side postoperatively, and it is difficult and painful for patients to attempt to fixate in primary position for the adjustment.

We and others42,251 perform supramaximal two-muscle recessions (Anderson procedure)25 of two horizontal muscles for head turns of less than 20 degrees associated with con-

genital nystagmus. We simultaneously tenotomize and reattach the other two horizontal rectus muscles to expand the null zone. We perform the Anderson procedure25 with simple tenotomy and reattachment of the other two horizontal rectus muscles for head turns of less than or equal to 20 degrees associated with infantile nystagmus. We have been impressed that the results are equal to those obtained with recess-resect surgery, but our impression (especially the null broadening) has not been verified by ocular motor data. It is unclear whether simple tenotomy and reattachment of the other two muscles would add any null-broadening effect. If one assumes that the surgical weakening of extraocular muscles increases exponentially with the amount of recession, and that large resections ultimately loosen up, it can be argued that this approach could produce an even greater therapeutic effect. If one further assumes that some of the therapeutic effect of four-muscle surgery comes from improved foveation and improved vision from the tenotomy alone, then this component is preserved without the large resection (which is especially painful for the child in the postoperative period).

For children with head turns greater than 20 degrees, we initially perform large two-muscle recessions combined with tenotomy of the other two horizontal muscles, reserving additional muscle resection for undercorrections following this approach. Because a Kestenbaum procedure expands null zone, it has been inferred that one need not produce a horizontal ophthalmoplegia to eliminate head turn. It is unclear whether simultaneous tenotomy of the other two horizontal rectus muscles during an Anderson procedure would further expand the null zone and reduce torticollis in this setting.566

As discussed above, Bagolini et al45 have emphasized that some large head turns must be conceptually distinguished from null positions; such patients use active blockage of nystagmus associated with increased innervational effort (similar to that seen with active convergence) to damp their nystagmus. In such patients, it may be necessary to induce a complete horizontal gaze palsy to eliminate the torticollis.

Rare patients with infantile nystagmus may assume a vertical head posture or a head tilt to achieve their null position. Vertical null positions can be eliminated with a recess-resect procedure of the vertical rectus muscles. (In a patient with a chin-down position, the inferior rectus muscles are resected, and the superior rectus muscles are recessed.) However, children with infantile nystagmus and vertical head positions may have unrecognized A or V patterns that cause them to assume a vertical head position to produce a large exophoria that allows them to converge and damp their nystagmus. It is therefore important to search carefully for an A or V pattern (which is difficult to detect in a child with nystagmus) before attributing a vertical head position to a vertical null position. If none is found, surgery can consist of recess-resect procedures of the vertical rectus muscles (for small vertical head positions) or combined