Chapter 18
Dissociated Strabismus
M. EDWARD WILSON
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INCIDENCE AND ASSOCIATIONS
OCULAR MANIFESTATIONS
TREATMENT
REFERENCES

Dissociated strabismus has intrigued and confused ophthalmologists for more than a century.1 These dissociated deviations usually are characterized by slow elevation, abduction, and extorsion of a nonfixating eye (Fig. 1) and appear to represent an exception to Hering's law of motor correspondence. The most often quoted early descriptions are from Bielschowsky.2,3 Over the years, these complex deviations have been given many descriptive titles, attesting to our incomplete understanding of their varied manifestations:
  • Dissociated vertical deviation
  • Dissociated vertical divergence
  • Alternating sursumduction
  • Occlusion hypertropia
  • Dissociated double hypertropia
  • Anatropia
  • Dissociated strabismus complex

Fig. 1. Dissociated strabismus. The nonfixating left eye is elevated, abducted, and extorted.

Dissociated vertical deviation (DVD), attributed to Raab,4 has become the most commonly used clinical label for this type of strabismus. This is an oversimplified description, however, because it implies a purely vertical deviation.

Although the slow elevation of the nonfixating eye is the most recognizable feature of dissociated strabismus, torsional or abducting components can predominate in one or both eyes, producing considerable diagnostic confusion. The diagnostic label dissociated strabismus complex (DSC) is preferred because it easily incorporates movements in the vertical, horizontal, and torsional axes.5–10 Latent or manifest-latent nystagmus and subnormal binocular vision also should be considered part of the complex. The DSC label avoids the awkward semantics of describing dissociated strabismus manifesting almost entirely horizontal or torsional movements as a DVD. Components of DSC include the following:

  • Dissociated elevation
  • Dissociated abduction
  • Dissociated extorsion
  • Latent nystagmus
  • Subnormal binocularity

Dissociated strabismus complex can be subdivided into dissociated vertical (DVD), horizontal (DHD), and torsional (DTD) deviations in records of patient examination findings. For instance, one eye may elevate markedly under cover with mild extorsion (4+ DVD, 1+ DTD), whereas the fellow eye may reveal marked abduction, moderate extorsion, and only mild elevation (4+ DHD, 3+ DTD, 1+ DVD) when covered. With this scheme, the familiar term of DVD still is used to describe the vertical component of the complex. However, horizontal and torsional movements are difficult to describe when DVD is used to name the entire complex. Because DHD has become a more clinically recognized entity, using DSC as an umbrella term avoids the temptation to overlook the intimate relationship between DVD and DHD, DTD, and latent nystagmus. If DVD or DHD is seen alone, it still can be labeled as such. On close observation, however, at least one other component of the complex nearly always is present. In a patient with prominent DVD, documenting subtle coexisting DTD, DHD, or latent nystagmus gives the examiner more confidence in the diagnosis of dissociated strabismus and further justifies the DSC label.

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INCIDENCE AND ASSOCIATIONS
Dissociated vertical deviation, if researched diligently, probably represents the most common hyperdeviation seen in a strabismus practice. Helveston11 recorded DVD in 11% of 1000 consecutive patients with strabismus or nystagmus. Wilson and Parks12 found DVD in 62% of 98 patients with congenital esotropia who were followed up to or beyond 6 years of age. Other investigators have reported this association in up to 80% of patients.13 The age of the patient at the time of surgical treatment for congenital esotropia does not affect the incidence of DVD.12 Incidence figures for all aspects of DSC may depend on how carefully subtle findings are sought. DHD, DTD, and latent nystagmus can be detected in most patients with DVD. Considerable variability can occur, however, since some components of the complex appear to be present during some examinations and absent during others. DHD prominent enough to require horizontal muscle surgery occurs in 5% or more of patients with congenital esotropia.14 This number is increasing as DHD becomes recognized more easily and differentiated more accurately from consecutive exotropia. DSC also can occur in association with acquired esotropia, exotropia, and hypertropia. DSC is not seen when high-grade stereopsis (bifixation) is preserved, however. Therefore, all patients with DSC who show signs of binocularity are classified as having the monofixation syndrome.

Inferior oblique muscle overaction develops in over 60% of patients with congenital esotropia.12 Therefore, DSC often coexists with inferior oblique overaction. DVD can simulate inferior oblique muscle overaction by becoming manifest in adduction as the nose interrupts fixation. Equally confusing is the association of a true hypertropia with DVD or a true esotropia or exotropia with DHD. These relationships are discussed later in this chapter. Latent or manifest-latent nystagmus occurs so frequently in association with DSC that it should be considered part of the complex. Latent nystagmus without coexisting congenital nystagmus rarely is seen in the absence of DSC.

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OCULAR MANIFESTATIONS
Dissociated strabismus complex almost always is a bilateral but asymmetric condition. In an analysis of 170 patients, von Noorden15 found bilaterality in 86% and asymmetry in 91%. When a unilateral dissociated deviation is detected initially, careful observation over several examinations usually reveals an asymmetric, bilateral DSC rather than a truly unilateral finding. Dissociated deviations may manifest spontaneously or may be controlled by binocular fusion mechanisms and remain latent. Even when manifest, they nearly always are intermittent, varying with the state of attention of the individual. Visual inattention often produces a larger deviation than can be measured by even prolonged alternate cover testing, and variability is the rule. Deviations can appear small and well controlled on one visit only to be large and to manifest spontaneously a brief time later. Complaints related to manifest DSC usually do not include diplopia. Although suppression usually is present, red lens testing can sometimes elicit diplopia. For DVD, the fact that the red light always appears below the white light—regardless of which eye has the red lens before it—is unique among vertical deviations. In addition, when fusional movements are measured, patients with DVD have large vertical fusional vergence amplitudes in both directions, which is another unique feature. Although dissociated horizontal and torsional movements are being recognized with greater frequency, DVD remains the predominant manifestation in most cases of DSC.

Placing base-down prisms before the higher eye or base-up prisms before the lower eye until all refixation movements are neutralized can quantitate a true hypertropia. The alternate cover test reveals these refixation movements to be upward in one eye and downward in the other eye, in accordance with Hering's law of equal motor innervation. The absence of upward refixation movements in either eye on alternate cover testing usually distinguishes DVD from true vertical tropia. In addition, the upward deviation is very slow (2 to 40 degrees per second) in DVD compared with true hypertropia (200 to 400 degrees per second).11 In addition, one or more of the other components of DSC (DTD, DHD, or latent nystagmus) almost invariably can be detected in patients with prominent DVD.

When one is attempting to quantify DVD, each eye must be measured separately. Prisms are placed base-down before the eye to be measured until it no longer rises behind cover. The measurement endpoint is not a true neutralization because the fellow eye has been rendered hypotropic by the prism. Even with this method, DVD measurements vary day to day—even moment to moment—and tend to increase with prolonged occlusion. For these reasons, a subjective 1+ to 4+ scale often is used to describe DVD. For a DVD estimated or measured less than 10 prism diopters (PD), a 1+ designation is often used. Deviations between 10 and 15 PD are labeled as 2+ , 15 to 20 as 3+ , and greater than 20 PD as 4+ . If a true hypertropia and DVD coexist, prism and alternate cover test neutralization of all upward refixation movements should be made first. The residual downward refixation movements of one or both eyes then can be identified as DVD. The true hypertropia and the more marked DVD usually is present on the same side. When one is documenting a combined hypertropia and a DVD, the hypertropia should be charted in prism diopters followed by the total deviation seen when the eye is dissociated. For instance, the combination of a right hypertropia (RHT) of 5 PD and a DVD of 15 PD would be charted as “RHT = 5 with DVD to 20.” If the fellow eye had a left hypotropia (LHoT) of 5 PD and a DVD of 10 PD, the chart might read “LHoT = 5 with DVD to 5 hyperdeviation.”

As stated previously, DSC can coexist with oblique muscle dysfunction. Wilson and Parks12 found DVD and inferior oblique muscle overaction (IOOA) occurring together in 45% of patients with congenital esotropia who were observed to at least 6 years of age. In addition, it is well known that in adduction the nose may act as an occluder, allowing DVD to simulate IOOA. A true hypertropia present in side gaze but absent in primary gaze is evidence that oblique muscle dysfunction exists. The adducted eye would manifest a hypotropia when superior oblique muscle overaction (SOOA) is present and a hypertropia when IOOA exists. The absence of a true hypertropia in adduction does not however exclude IOOA occurring in conjunction with SOOA. With coexistence of DVD and IOOA, the adducted eye may elevate under cover from either disorder. The abducted eye, when covered, has opposing forces at work. The DVD causes the eye to float upward while the IOOA drives the abducted eye downward. A true hypertropia is seen only if the IOOA-stimulated hypotropia of the abducting eye overcomes the DVD-stimulated hyperdeviation. This reasoning also can be used to help verify the coexistence of DVD and either IOOA or SOOA. Oblique muscle dysfunction causes the DVD to appear incomitant. IOOA reduces DVD in abduction, and SOOA reduces DVD in adduction. In other words, if DVD is evident in primary gaze but much less elevation is present behind cover when either eye is in abduction, bilateral IOOA should be suspected and a V pattern sought to confirm the diagnosis. If elevation behind cover is much less in adduction, SOOA should be suspected and an A pattern sought to verify the diagnosis. Care must be taken to anticipate the effect on DVD when coexisting oblique muscle dysfunction is treated surgically.

Torticollis has been documented in up to 35% of patients with DVD when an ocular fixation preference is present.16 Patients with alternating fixation are much less likely to manifest a head tilt secondary to DVD. When present, the head tilt usually is toward the side of the nonfixating eye with the larger, more often manifest, DVD. Thus, the DVD usually increases with forced tilt away from the eye with the more severe DVD and decreases on tilt toward the eye with more severe DVD. This tilting pattern is opposite from that seen in superior oblique muscle palsy, in which the hypertropia increases on ipsilateral tilt and decreases on contralateral tilt. Exceptions to this pattern occur when patients with DVD maintain a head posture opposite from that predicted and show forced tilt changes more like those of superior oblique muscle palsy (Fig. 2). The Parks three-step test is misleading in these patients and therefore should not be applied. In rare patients, the torticollis cannot be related obviously to a qualitative or quantitative change in the DVD. To avoid being misled, one should not apply the Parks three-step test to patients with DSC.

Fig. 2. Dissociated strabismus complex. (A) While the patient maintains a rightward head tilt, DSC is well controlled. (B) Forced leftward head tilt produces a manifest left DVD. (C) When the patient is fixating with the right eye, a left DVD is manifest. (D) On fixation with the left eye, a right DHD is manifest. Mild DVD also was present. After recession of both superior rectus muscles and the right lateral rectus muscle, the DSC is well controlled. A small leftward head tilt is present.

The Bielschowsky phenomenon3 is unique to DSC. It can be demonstrated most easily when DVD and amblyopia are present. Downward movement of the elevated occluded nonfixating eye occurs when filters of increasing density are placed before the fixating eye. The eye behind cover may even come to rest below primary position. A Bagolini graded red filter bar helps elicit the Bielschowsky phenomenon. Alternatively, illumination to the fixating eye can be progressively reduced by rotating two polarized filters on one another to create a darkening filter. Increasing illumination to the fixating eye also can produce the Bielschowsky phenomenon. The phenomenon has also been demonstrated in the horizontal plane when prominent DHD is present.5

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TREATMENT
Dissociated strabismus complex, when manifest, does not often cause diplopia. It disrupts binocular vision, however, and can be disfiguring. Even a small DVD can appear prominent as the eye elevates and sclera begins to be visible at the lower eyelid margin. Also, the exodeviation produced by DHD rarely avoids detection and often prompts complaints from parents of affected patients even when the deviation is manifest infrequently. A prominent abnormal head posture also can be an indication for treatment. In some patients who experience alternating fixation, manifest DVD predominates when one eye deviates and DHD predominates when fixation switches and the fellow eye drifts (see Fig. 2). Despite its ability to be disfiguring, most DSC is small and well controlled. No treatment is usually needed. This is fortunate because the condition cannot be eliminated totally by any of the available treatments. Successful treatment merely reduces the frequency and magnitude of spontaneously manifest DSC so that it rarely—if ever—is seen at home. Despite treatment, dissociated strabismus almost always still can be detected in the office during alternate cover testing. No patient is cured of DSC, and recurrence of manifest deviations is common even after aggressive treatment.

Nonsurgical treatment, although theoretically appealing, usually is not effective. Because DSC often is asymmetric, nonsurgical treatment involves ways to promote a switch in fixation preference to the eye that deviates most often. Because DSC manifests only in a nonfixating eye, promoting fixation with the eye known to have marked DSC keeps that eye from deviating. Limited success has been reported with both optical and pharmacologic penalization techniques designed to blur the eye that has less DSC and switch fixation to the eye with more DSC.15,17 These treatments are not likely to reduce the prevalence of manifest DSC unless the DSC is markedly asymmetric and a fixation switch is produced. The Worth four-dot test and a variety of vectographic tests can be used to verify a switch of fixation to the nondominant, dissociating eye.

Most cases of symptomatic DVD or DHD are managed surgically. Standard surgical treatments for DVD have been shown to have no effect on DHD.18 Therefore, if prominent, DHD requires specific surgical strategies. DTD usually is not disfiguring and is not treated surgically. Latent nystagmus is considered part of DSC and deserves mention. Latent nystagmus may become manifest even when an eye is not covered. This occurs when horizontal strabismus or DVD disrupts binocular function. Treatment that restores binocularity often converts a manifest-latent nystagmus back to a latent nystagmus.

Recession of the superior rectus muscles is the most common treatment for DVD. Surgery is usually performed bilaterally unless the DVD is strictly unilateral or dense amblyopia is present. When performed unilaterally, a moderate superior rectus muscle recession of 5 to 9 mm is typical.19 A hypotropia often is produced that lasts days, weeks, or longer. Fewer undercorrections occur when unilateral surgery is performed for DVD. A switch in fixation may occur, however, resulting in manifest DVD in the previously asymptomatic eye. Some surgeons therefore advocate bilateral surgery either symmetrically or asymmetrically for all patients with DVD.20

If asymmetric, the quantity of surgery is determined by the severity of DVD in each eye. When performing bilateral superior rectus muscle recessions for DVD, I prefer large (7 to 10 mm) symmetric recessions, regardless of the asymmetry in DVD severity between the eyes. If a true hypertropia coexists with DVD, however, I usually perform more superior rectus muscle recession on the hypertropic eye. The hypertropia usually is found in the eye with the larger DVD, further justifying asymmetric recessions for these patients. When marked DVD (greater than 15 PD) coexists with inferior oblique muscle overaction, simultaneous surgery on the four vertical muscles may be indicated, consisting of a weakening procedure on both superior rectus muscles and both inferior oblique muscles.21 Limiting the superior rectus muscle recessions to 8 mm and the inferior oblique recessions to 10 mm reduces the likelihood that this combined surgery will produce a functionally important up-gaze deficit. However, inferior oblique anterior transposition (discussed in detail in the following section) has been combined with superior rectus muscle recessions of up to 10 mm without producing severe up-gaze deficits in a limited number of patients.21,22 Alternatively, inferior rectus muscle resections have been shown to be effective in the treatment of residual DVD after superior rectus muscle recessions.23 Some surgeons advocate inferior rectus muscle resections as a primary treatment for DVD24 despite the lower eyelid elevation, flattening, and fullness that often result after this procedure.

Posterior fixation sutures placed 12 to 15 mm posterior to the superior rectus muscle insertion either alone or in combination with a superior rectus muscle recession have been advocated as an effective treatment for DVD.25 Esswein and coworkers,26 however, have reported that although the effectiveness of 3- to 5-mm superior rectus muscle recessions combined with posterior fixation sutures was excellent at 6 months postoperatively (87% corrected or improved), a failure rate of 55% was documented 3 years after surgery. In contrast, the success rate of 7- to 9-mm superior rectus muscle recessions diminished only slightly over time, with 86% corrected or improved at 6 months, 80% after 1 year, 77% after 2 years, and 72% after 3 years. I do not use posterior fixation sutures for the treatment of DVD.

Anterior transposition of the inferior oblique muscle (IOAT), a modified recession procedure developed to treat severe inferior oblique muscle overaction,27 also has been used to treat DVD.28–31 When DVD and inferior oblique muscle overaction coexist, the IOAT procedure has been shown to effectively treat DVD up to about 15 PD.29 Larger DVDs, of 20 PD or more, are not well treated by IOAT. IOAT effectively eliminates marked inferior oblique muscle overaction. Reattaching the muscle at or anterior to the inferior rectus muscle insertion converts the muscle from an elevator to an antielevator.32 Stager33 studied the inferior oblique muscle's neurovascular bundle as a new functional origin after IOAT. Both the new origin and the new insertion of the inferior oblique muscle parallel the inferior rectus muscle. This altered anatomy produces a cocontraction of sorts with the superior rectus muscle. The inferior oblique contracts on attempted elevation and yet has a functional origin and insertion parallel to the inferior rectus muscle. This altered anatomy may help explain why IOAT can cause an updaze deficit in abduction.

Other complications also have been seen with the IOAT procedure. If the muscle is spread too widely when it is reattached, a characteristic Y or T pattern is produced, characterized by divergence in far up-gaze and the appearance of residual inferior oblique muscle overaction.32 A trade-off appears to exist in which further anterior placement of the inferior oblique muscle corrects more DVD but also is more likely to cause an up-gaze deficit and a T pattern. Gonzalez and Klein34 have reported an inferior oblique resection combined with anterior transposition with good control of larger DVD. Severe up-gaze deficit is a risk with this procedure, however.

IOAT also has been suggested as a prophylactic surgery for DVD in patients with inferior oblique muscle overaction and at high risk for DVD. Mims and Wood28 performed IOAT on 61 patients with congenital esotropia with bilateral inferior oblique muscle overaction. They placed the inferior oblique muscle 2 mm anterior to the temporal border of the inferior rectus muscle insertion. With an average follow-up of 27 months, only one patient needed surgery for DVD compared with nine in a control group of patients with congenital esotropia who had not undergone inferior oblique muscle surgery. The IOAT procedure has been recommended whenever inferior oblique muscle overaction is present in a patient with mild coexisting DVD or when the patient is at high risk for DVD. Other procedures that have been used to treat DVD include superior oblique tendon tuck or resection,35 which can result in Brown syndrome, and botulinum toxin injection to the superior rectus muscles,36 which invariably leads to marked, albeit transient, ptosis.

When DHD is prominent and manifest frequently, a surgical plan specific to the horizontal drift of the eyes needs to developed. Treating the DVD surgically is not likely to alter the DHD.18 Surgical treatment for symptomatic DHD usually involves unilateral or bilateral lateral rectus muscle recession.5,9,37 Raab (personal communication, 1987) and Romero-Apis and Castellanos-Bracamontes8 recommended the addition of posterior fixation sutures on the lateral rectus muscles for this condition. For asymmetric or unilateral DHD, 4- to 8-mm ipsilateral lateral rectus muscle recessions are effective.5,37 The quantity of recession is based on the quantity of the DHD, the presence of superimposed esotropia or exotropia, and perhaps whether congenital esotropia has been treated previously. Bilateral lateral rectus muscle recessions carry a higher risk of postoperative esotropia unless a true exotropia is present coincident with the DHD.

Just as a hypotropia can have an overlying DVD, esotropia can have an overlying DHD. This combination can masquerade as variable-angle esotropia or may present as an esodeviation when the patient is visually attentive and an exodeviation when the patient is visually inattentive. Patients presenting with the combination of esotropia and DHD can be challenging to evaluate and treat. Accurately measuring the deviation with alternate cover testing may be difficult. The esodeviation should be quantitated using a rapid alternate cover test technique while the patient fixates on an accommodative distant target. A slower alternate cover test allows the eye behind the cover time to dissociate, and the DHD may become manifest. The quantity of DHD seen with visual inattention almost always is larger than that measured during even prolonged alternate cover testing (Fig. 3). Often, the DHD must be estimated or measured using corneal light reflections.

Fig. 3. A marked left DHD is seen with visual inattention that is much larger than could be measured during even prolonged alternate cover testing.

When an esodeviation and DHD (an exodeviation) coexist, care must be taken not to make one worse while treating the other. Surgical options include the following:

  1. Treat the DHD alone with lateral rectus muscle recessions with or without posterior fixation sutures. This approach is advised if the esotropia is a stable microtropia associated with the monofixation syndrome or a well-controlled accommodative esotropia. Although the esotropia will appear larger during the first postoperative week, it usually will return to the preoperative quantity when healing has occurred.
  2. Treat the esotropia alone. This approach is recommended if the esotropia is functionally symptomatic and the DHD is small or rarely manifest. However, esotropia surgery (especially when lateral rectus muscles are resected) may worsen or unmask DHD. Consider reducing the surgical dosage for the esotropia surgery or warning the patient's parents that DHD may necessitate further treatment in the future.
  3. Treat the DHD with unilateral or bilateral lateral rectus muscle recessions and the esotropia with unilateral or bilateral medial rectus muscle recessions. Posterior fixation sutures can be added to the medial or lateral rectus muscles. This approach is recommended when both the esotropia and the DHD are functionally symptomatic. Because the esotropia is present with visual attentiveness and the DHD is present during visual inattentiveness, it may be reasonable to recess medial and lateral rectus muscles simultaneously. Larger dosages of surgery will be needed compared with either DHD or esotropia treated alone.

In summary, dissociated deviations include movements in the vertical, horizontal, and torsional axes. DVD should not be used to refer to the entire complex. To avoid semantic confusion, DSC should be subdivided into its vertical (DVD), horizontal (DHD), and torsional (DTD) components when patient examination data are recorded. Latent nystagmus should be included as part of the complex. DVD and DHD require separate surgical strategies but often are treated surgically together. True hypertropia, hypotropia, esotropia, or exotropia can coexist with DSC. Treatment must be individualized for these patients addressing both the dissociated and associated portions of the strabismus.

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REFERENCES

1. Stevens GT: On double vertical strabismus. Ann Ocularist 113:225, 1895

2. Bielschowsky A: Die einseitigen und gegensinnigen (“dissoziierten”) Vertikalbewegungen der Augen. Graefes Arch Ophthalmol 1930;125:493

3. Bielschowsky A: Lectures on Motor Anomalies, p 17. Hanover: Dartmouth College Publications, 1940

4. Raab EL: Dissociative vertical deviation. J Pediatr Ophthalmol Strabismus 7:146, 1970

5. Wilson ME, McClatchey SK: Dissociated horizontal deviation. J Pediatr Ophthalmol Strabismus 28:90, 1991

6. Wilson ME: Dissociated vertical deviation. In Margo CE (ed): Diagnostic Problems in Clinical Ophthalmology, p 769. Philadelphia: WB Saunders, 1994

7. Wilson ME: The dissociated strabismus complex [Correspondence]. Binocular Vision 8:45, 1993

8. Romero-Apis D, Castellanos-Bracamontes A: Dissociated horizontal deviation: Clinical findings and surgical results in 20 patients. Binocular Vision 7:135, 1992

9. Wilson ME, Saunders RA, Sinatra RB: The Surgical Treatment of Dissociated Horizontal Deviation. Poster presented at the annual meeting of the American Academy of Ophthalmology, Chicago, Nov 14-18, 1993

10. Wilson ME: Vertical strabismus. In Wright KW (ed): Text and Atlas of Pediatric Ophthalmology, p 211. St. Louis: CV Mosby, 1995

11. Helveston EM: Dissociated vertical deviation: A clinical and laboratory study. Trans Am Ophthalmol Soc 78:734, 1980

12. Wilson ME, Parks MM: Primary inferior oblique overaction in congenital esotropia, accommodative esotropia and intermittent exotropia. Ophthalmology 96:950, 1989

13. Calhoun JH: Dissociated vertical deviation. In Spaeth GL, Catz LJ, (eds): Current Therapy in Ophthalmic Surgery, p 286. Toronto/Philadelphia: BC Decker, 1989

14. Enke ES, Stewart SA, Scott WE et al: The prevalence of dissociated horizontal deviations in congenital esotropia. Am Orthoptic J 44:109, 1994

15. Von Noorden GK: Binocular vision and ocular motility: Theory and management of strabismus, p 341. 4th ed. St. Louis: CV Mosby, 1990

16. Bechtel RT, Kushner BJ, Morton GV: The relationship between dissociated vertical divergence (DVD) and head tilts. J Pediatr Ophthalmol Strabismus 33:303, 1996

17. Simon JW, Bayramler H, Kamath S: Atropine penalization therapy of dissociated vertical deviations. Binocular Vision Strabismus Q 11:263, 1996

18. Wheeler DT, Enke ES, Scott WE: Surgical management of dissociated horizontal deviation associated with congenital esotropia. Binocular Vision Strabismus Q 11:256, 1996

19. Braverman DE, Scott WE: Surgical correction of dissociated vertical deviations. J Pediatr Ophthalmol 14:337, 1977

20. Magoon E, Cruciger M, Jampolsky A: Dissociated vertical deviations: An asymmetric condition treated with large bilateral superior rectus recession. J Pediatr Ophthalmol Strabismus 19:152, 1982

21. Varn MM, Saunders RA, Wilson ME: Combined bilateral superior rectus muscle recession and inferior oblique muscle weakening for dissociated vertical deviation. J Am Assoc Pediatr Ophthalmol Strabismus 1:134, 1997

22. Roberts E, Saunders RA, Wilson ME: Surgery for vertical head position in null point nystagmus. J Pediatr Ophthalmol Strabismus 33:219, 1996

23. Kapp MBE, von Noorden GK: Treatment of residual dissociated vertical deviation with inferior rectus resection. J Pediatr Ophthalmol Strabismus 31:262, 1994

24. Noel LP, Parks MM: Dissociated vertical deviation: Associated finding and results of surgical treatment. Can J Ophthalmol 17:10, 1982

25. Sprague JB, Moore S, Eggers H et al: Dissociated vertical deviation, treatment with the Faden operation of Cuppers. Arch Ophthalmol 98:465, 1980

26. Esswein MB, von Noorden GK, Coburn A: Comparison of surgical methods in the treatment of dissociated vertical deviation. Am J Ophthalmol 113:287, 1992

27. Elliot RL, Nankin SJ: Anterior transposition of the inferior oblique. J Pediatr Ophthalmol Strabismus 18:35, 1981

28. Mims JL, Wood RC: Bilateral anterior transposition of the inferior obliques. Arch Ophthalmol 107:41, 1989

29. Burke JP, Scott WE, Kutschke PJ: Anterior transposition of the inferior oblique muscle for dissociated vertical deviation. Ophthalmology 100:245, 1993

30. Kratz RE, Rogers GL, Bremer DL et al: Anterior tendon displacement of the inferior oblique for DVD. J Pediatr Ophthalmol Strabismus 26:212, 1989

31. Milot J, Tremblay OCC, Quellette C: Anterior transposition of the inferior oblique for dissociated vertical deviation with inferior oblique overaction. Can J Ophthalmol 29:284, 1994

32. Kushner BJ: Restriction of elevation in abduction after inferior oblique anteriorization. JAAPOS 1:55, 1997

33. Stager DR, Weakley DR, Stager D: Anterior transposition of the inferior oblique: Anatomic assessment of the neurovascular bundle. Arch Ophthalmol 110:360, 1992

34. Gonzalez C, Klein B: Myectomy and anterior transposition of the inferior oblique muscle: A new surgical procedure and its results in 49 operations. Binocular Vision Eye Muscle Q 8:249, 1993

35. Richard JM: Combined superior oblique muscle tendon resection and inferior oblique muscle recession for dissociated vertical deviation: 25 cases. Binocular Vision 2:137, 1987

36. McNeer KW: Botulinum toxin injection into the superior rectus muscle of the non-dominant eye for dissociated vertical deviation. J Pediatr Ophthalmol Strabismus 26:162, 1989

37. Wilson ME, Saunders RA, Berland JE: Dissociated horizontal deviation and accommodative esotropia: Treatment options when an eso and an exodeviation co-exist. J Pediatr Ophthalmol Strabismus 32:228, 1995

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