Treatment

Prisms

For the patient with nystagmus, use of prisms can improve head positions by shifting the retinal image toward the null point. Also, prisms can improve vision by inducing convergence. They can be used as the sole treatment of nystagmus or as a trial to predict surgical success. With powers ranging from 1Δ–40Δ, Fresnel press-on prisms, inexpensive plastic pieces that can be cut and then applied to glasses, can be used for both purposes, as powers of 10Δ–20Δ are often required. Ground-in prisms cause less distortion and are preferred for patients who require smaller amounts of prism.

To correct head positions, each prism is mounted with the apex pointing toward the null point. For example, for a patient with a left head turn and a null point in right gaze, the prism before the right eye should be oriented base-in, and the prism before the left eye should be oriented base-out. This shifts the image to the right and decreases the amount of head turn that the patient requires to gain the same visual benefit. If this technique improves the head position, strabismus surgery is also likely to be effective.

Prism spectacles may improve visual acuity by stimulating fusional convergence, which damps the nystagmus. In this situation, base-out prisms are placed in front of both eyes in amounts determined by trial and error.

Surgery for Nystagmus

Extraocular muscle surgery for nystagmus is indicated for correction of an abnormal head position, which is achieved by shifting the null point closer to the primary position. Surgery can also improve vision by decreasing nystagmus intensity (frequency times amplitude) and consequently foveation time. The types of surgery typically recommended are conjugate recessions in each eye (Anderson procedure), a recession-resection on both eyes (Kestenbaum procedure), or a recession of all 4 horizontal rectus muscles. See Chapter 14 for discussion of some of the surgical procedures mentioned in this chapter.

In a Kestenbaum or Anderson procedure, the eyes are surgically rotated toward the direction of the head turn and away from the null point or preferred gaze position. Each eye is operated on to move the eyes in the same direction. For example, if a patient with congenital nystagmus has a left head turn and null point in right gaze, the eyes are surgically rotated to the left by recession of the right lateral and left medial rectus muscles and by resection of the right medial and left lateral rectus muscles, thereby shifting the null point toward the primary position (Fig 13-3).

Figure 13-3 A, Congenital motor nystagmus with the null point in right gaze. B, Null point shifted by the Kestenbaum procedure, reducing the head turn. (Courtesy of Edward L. Raab, MD.)

The amounts of recession-resection performed are listed in Table 13-4. The total amount of surgery for each eye (as measured in millimeters) is equal in order to rotate each globe an equal amount. For head turns of 30°, 40% augmentation is recommended; for turns of 45°, augmentation of 60% is employed. The augmented procedures may cause restriction of motility, which is usually necessary to achieve a satisfactory result.

Table 13-4

If vertical torticollis is present with congenital nystagmus, chin-up or chin-down posturing may be ameliorated in some cases by vertical prism (again, apex toward the null point) or by surgery on the vertical rectus muscles or the oblique muscles. As with surgery for horizontal nystagmus, the eyes are rotated away from the null point. Thus, if a chin-up, eyes-down head position is present, the inferior rectus muscles are recessed and the superior rectus muscles are resected. The amount of surgery is usually 8–10 mm of recession and resection of the vertical rectus muscles of each eye. Alternatively, combined weakening of a vertical rectus muscle and an oblique muscle in each eye can be used. For a chin-up head position, the inferior rectus and superior oblique muscles are weakened; for chin-down, the superior rectus and inferior oblique muscles are weakened. Improvement in the head position of nystagmus patients with a head tilt has been reported with torsional surgery involving the oblique muscles or transposition of the vertical rectus muscles.

When there is no eccentric null point and the Kestenbaum procedure is not indicated, recession of all the horizontal rectus muscles to a position posterior to the equator has been offered as an alternative. The amount of surgery is usually in the range of 8–10 mm of recession of both medial rectus muscles and 10–12 mm of recession of both lateral rectus muscles. Recent studies have found that merely disinserting and reattaching the horizontal rectus muscles, without recession or resection, produces similar results with presumably less risk of inducing new strabismus. This procedure

results in improved foveation time on electronystagmography and secondary indicators of visual function such as recognition time; however, the effect on visual acuity is modest—an average improvement of about 1 line. Nystagmus surgery in the absence of abnormal head position is controversial.

Surgery for nystagmus blockage syndrome involves recession of the medial rectus muscles, usually with amounts that are larger than normal for the amount of esotropia. This may be combined with posterior fixation sutures (see Chapter 14).

For nystagmus patients with strabismus, surgery to shift the null point must be performed on the dominant fixating eye; surgery on the nondominant eye is then adjusted to account for the strabismus. For example, a patient who is right-eye dominant and has a right head turn and null point in left gaze would undergo a right medial rectus recession and right lateral rectus resection in the amounts indicated in Table 13-4. This would reduce esotropia or increase exotropia. Surgery on the nonpreferred eye is designed to correct the remaining deviation.

Hertle RW, Dell’Osso LF, FitzGibbon EJ, Thompson D, Yang D, Mellow SD. Horizontal rectus tenotomy in patients with congenital nystagmus: results in 10 adults. Ophthalmology. 2003;110(11):2097–2105.

Yang MB, Pou-Vendrell CR, Archer SM, Martonyi EJ, Del Monte MA. Vertical rectus muscle surgery for nystagmus patient with vertical abnormal head posture. J AAPOS. 2004;8(4):299–309.