Surgical results of patients with A-pattern horizontal strabismus

Morphological Differences in the Inferior Oblique Muscles from Subjects with Over-elevation in Adduction

Purpose

We examined inferior oblique muscles from subjects with over-elevation in adduction for characteristics that might shed light on the potential mechanisms for their abnormal eye position.

Methods

The inferior oblique muscles were obtained at the time of surgery in subjects diagnosed with either primary inferior oblique overaction or Apert syndrome. The muscles were frozen and processed for morphometric analysis of myofiber size, central nucleation, myosin heavy chain (MyHC) isoform expression, nerve density, and numbers of neuromuscular junctions per muscle section.

Results

The inferior oblique muscles from subjects with Apert Syndrome were smaller, and had a much more heterogeneous profile relative to myofiber cross-sectional area compared to controls. Increased central nucleation in the Apert syndrome muscles suggested on-going myofiber regeneration or reinnervation over time. Complex changes were seen in the MyHC isoform patterns that would predict slower and more sustained contractions than in the control muscles. Nerve fiber densities were significantly increased compared to controls for the muscles with primary inferior oblique overaction and Apert syndrome that had no prior surgery. The muscles from Apert syndrome subjects as well as those with primary inferior oblique overaction with no prior surgery had significantly elevated numbers of neuromuscular junctions relative to the whole muscle area.

Conclusions

The muscles from both sets of subjects were significantly different from control muscles in a number of properties examined. These data support the view that despite similar manifestations of eye misalignment, the potential mechanism behind the strabismus in these subjects is significantly different.

Factors influencing the result of superior oblique weakening procedures in patients with superior oblique overaction in horizontal strabismus

Background

Few studies have evaluated the surgical outcome of superior oblique weakening procedures in patients with superior oblique overaction associated with exotropia or esotropia. This study aimed to evaluate the outcome of superior oblique muscle weakening and the influencing factors in patients with superior oblique overaction.

Methods

The medical charts of 37 patients (55 eyes) with superior oblique overaction associated with esotropia or exotropia who were treated with a superior oblique weakening procedure at the Seoul National University Hospital from January 2010 to June 2017 were retrospectively reviewed. Superior oblique overaction was graded using, a 6-point scale ranging from + 0.5 to + 3, and pre- and postoperative grades were recorded for all patients.

Results

The mean age of the patients was 91.81 ± 59.37 months. Superior oblique muscle suture spacer and superior oblique posterior tenectomy were performed for 17 (23 eyes) and 20 (32 eyes) patients, respectively. Surgical success was achieved in 15 (65.2%) eyes in the suture spacer group and 23 (71.9%) eyes in the posterior tenectomy group. Surgical success was achieved for 69.1% (38/55 eyes) of patients. Dissociated vertical deviation exhibited a significant negative association with the surgical success rate (p < 0.001).

Conclusions

There was no significant difference in surgical success rate between the superior oblique posterior tenectomy and superior oblique suture spacer groups in superior oblique overaction associated with horizontal strabismus. Associated dissociated vertical deviation can affect the surgical success of the superior oblique weakening procedure.

Stereopsis before and after Inferior Oblique Weakening Surgery

Purpose

To analyze stereopsis change before and after inferior oblique weakening surgery.

Methods

We retrospectively reviewed the medical records of 31 patients who had undergone inferior oblique weakening surgery. The factors analyzed included sex, age at surgery, preoperative and postoperative visual acuity (VA), time from first detection to surgery, degree of inferior oblique overaction (IOOA), primary/secondary IOOA, exotropia/hypertropia, bilaterality, and type of surgery.

Results

Eighteen patients with a mean age 7.3 ± 3.1 years exhibited stereopsis of 60 arc seconds or better before surgery and 17 had stereopsis better than 60 arc seconds after surgery. Postoperatively, stereopsis improved in 13 patients and deteriorated in 9. Better preoperative VA and the absence of superior oblique underaction were associated with better preoperative stereopsis. Better preoperative VA, postoperative VA, and the presence of head tilt were associated with better postoperative stereopsis. Unilateral inferior oblique weakening surgery and accompanying hypertropia were associated with improved stereopsis, while the absence of hypertropia was associated with deteriorated stereopsis.

Conclusions

In this retrospective study, 58.1% of patients tended to have bifoveal fixation. When a vertical deviation is present in the primary position due to unilateral IOOA, IO weakening surgery can be expected to improve binocular function.

Improvement of Eye Alignment in Adult Strabismic Monkeys by Sustained IGF-1 Treatment

Purpose

The goal of this study was to determine if continuous application of insulin-like growth factor-1 (IGF-1) could improve eye alignment of adult strabismic nonhuman primates and to assess possible mechanisms of effect.

Methods

A continuous release pellet of IGF-1 was placed on one medial rectus muscle in two adult nonhuman primates (M1, M2) rendered exotropic by the alternating monocular occlusion method during the first months of life. Eye alignment and eye movements were recorded for 3 months, after which M1 was euthanized, and the lateral and medial rectus muscles were removed for morphometric analysis of fiber size, nerve, and neuromuscular density.

Results

Monkey 1 showed a 40% reduction in strabismus angle, a reduction of exotropia of approximately 11° to 14° after 3 months. Monkey 2 showed a 15% improvement, with a reduction of its exotropia by approximately 3°. The treated medial rectus muscle of M1 showed increased mean myofiber cross-sectional areas. Increases in myofiber size also were seen in the contralateral medial rectus and lateral rectus muscles. Similarly, nerve density increased in the contralateral medial rectus and yoked lateral rectus.

Conclusions

This study demonstrates that in adult nonhuman primates with a sensory-induced exotropia in infancy, continuous IGF-1 treatment improves eye alignment, resulting in muscle fiber enlargement and altered innervational density that includes the untreated muscles. This supports the view that there is sufficient plasticity in the adult ocular motor system to allow continuous IGF-1 treatment over months to produce improvement in eye alignment in early-onset strabismus.

Effects of Bilateral Superior Oblique "Hang-Back" Recession in Treatment of A-pattern Strabismus with Superior Oblique Overaction

PURPOSE

To investigate the efficacy and safety of bilateral hang-back recession of superior oblique (SO) muscles in the treatment of A-pattern strabismus with superior oblique overaction (SOOA).

METHODS

Thirty-one (31) patients (62 eyes) with A-pattern horizontal deviation and SOOA underwent hang-back recession of SO and retrospective analysis of the surgical amount of hang-back recession of SO, preoperative and postoperative A-pattern, ocular motility, and corrected objective torsion. Patients were evaluated before and 6 to 9 months after surgery.

RESULTS

The average A-pattern horizontal deviation was 27.58 ± 11.47 prism diopters (PD) before surgery and 3.48 ± 3.70 PD after surgery (n=31, P<0.05). The mean corrected A-pattern was horizontal deviation 24.10 ± 10.32 PD. The average scale of SOOA on a scale of +1 to +4 was +3.05 ± 0.80 before surgery and +0.42 ± 0.50 after surgery in 62 eyes (P<0.05). The mean corrected objective torsion was 4.91° ± 4.53°. The surgical amount of SO hang-back recession ranged from 4 to 10 mm (mean: 7.62 ± 1.18 mm), which was related to the preoperative A-pattern and corrected A-pattern. There were no surgical complications.

CONCLUSIONS

SO hang-back recession is a safe and efficient option for A-pattern caused by SOOA.

Pattern Strabismus: Where Does the Brain's Role End and the Muscle's Begin?

Vertically incomitant pattern strabismus comprises 50% of infantile horizontal strabismus. The oblique muscle dysfunction has been associated with pattern strabismus. High-resolution orbit imaging and contemporary neurophysiology studies in non-human primate models of strabismus have shed light into the mechanisms of pattern strabismus. In this review, we will examine our current understanding of etiologies of pattern strabismus. Speculated pathophysiology includes oblique muscle dysfunction, loss of fusion with altered recti muscle pull, displacements and instability in connective tissue pulleys of the recti muscles, vestibular hypofunction, and abnormal neural connections. Orbital mechanical factors, such as abnormal pulleys, were reported as a cause of pattern strabismus in patients with craniofacial anomalies, connective tissue disorders, and late-onset strabismus. In contrast, abnormal neural connections could be responsible for the development of a pattern in infantile-onset strabismus. Pattern strabismus is likely multifactorial. Understanding the mechanisms of pattern strabismus is pivotal to determine an appropriate surgical treatment strategy for these patients.

Effect of superior oblique weakening on vertical alignment and horizontal and vertical incomitance in patients with A-pattern strabismus

PURPOSE

To determine the relationship between the magnitude of preoperative A pattern and the correction of vertical alignment and horizontal and vertical incomitance in patients treated with superior oblique muscle-weakening procedures for A-pattern strabismus.

METHODS

The records of consecutive patients who underwent surgery for A-pattern strabismus between 1997 and 2008 were retrospectively reviewed. Both horizontal (from up- to downgaze) and vertical (from right to left gaze) incomitance were assessed.

RESULTS

Twenty-six patients were treated with superior oblique muscle-weakening procedures (either tendon spacer or nasal or posterior 7/8 temporal tenotomy, with or without simultaneous rectus muscle surgery). In these patients, the A pattern improved from 36Δ preoperatively (range, 15Δ-75Δ) to 6Δ postoperatively (range, 0Δ-16Δ). The magnitude of the reduction in A pattern correlated strongly with the size of preoperative A pattern (r=0.92), whereas the reduction in the magnitude of the vertical incomitance correlated weakly with the magnitude of the preoperative deviation (r=0.56). There was no significant correlation between the magnitude of the A pattern and the vertical incomitance (r=0.25). Of the 9 patients with preexisting primary position vertical deviation≥6Δ, 5 required additional vertical rectus muscle surgery.

CONCLUSIONS

Superior oblique muscle-weakening surgery improved the A pattern but did not reliably improve the primary position vertical deviation and lateral gaze vertical incomitance. Patients with associated primary position vertical deviations of >6Δ preoperatively tended to have a greater likelihood of requiring additional strabismus surgery.

Decreased postoperative drift in intermittent exotropia associated with A and V patterns

INTRODUCTION

Few data exist concerning postoperative drift in patients with intermittent exotropia who have coexistent A or V patterns. In addition, the impacts of pattern collapse and surgical method on postoperative drift have not been well addressed.

METHODS

We retrospectively reviewed the records of 132 patients who had surgery for intermittent exotropia and had >or=6 months' follow-up. Mean postoperative drift in 66 patients with pattern exotropia was compared with a nonpattern (comitant) group matched for surgeon, age, surgical method, and initial deviation. Postoperative drift was calculated by subtracting the deviation at postoperative day 1 from that at approximately 6 weeks, 6 months, 9 months, and >1 year.

RESULTS

Pattern and comitant groups were similar in mean +/- SD age (15 +/- 17 years), follow-up (2.3 +/- 2 years), preoperative exotropia (23(Delta) +/- 11(Delta)), initial postoperative deviation (1(Delta) +/- 5(Delta) esotropia), and surgical technique. Patients with pattern intermittent exotropia showed significantly (p < 0.02) less exotropic drift postoperatively at all times than did patients without a pattern. In contrast to undercorrected patients, in those who were sufficiently overcorrected, the effect of pattern became statistically insignificant after 6 months. Patients with persisting postoperative patterns had a significantly less postoperative drift (p < 0.01).

CONCLUSION

Postoperative drift in patients with A- or V-pattern intermittent exotropia is consistently less than in comitant exotropia, particularly if the pattern persists postoperatively and if the exotropia is undercorrected. Therefore, surgeons should consider smaller early overcorrections in pattern than comitant intermittent exotropia. Lesser postoperative drift in pattern exotropia may suggest differing underlying causes of pattern vs nonpattern exotropia.

Z-tenotomy of the superior oblique tendon and horizontal rectus muscle surgery for A-pattern horizontal strabismus

PURPOSE

Few studies have investigated combined surgeries for horizontal deviation and A pattern caused by superior oblique overaction (SOOA). This study presents our experience with combined surgery and examines the effect of the type of strabismus and prior surgery on outcome.

METHODS

The medical records of patients who underwent combined surgery for horizontal deviation occurring with A-pattern misalignment from 2000 through 2004 were reviewed. The procedure consisted of horizontal extraocular muscle recession or resection with superior oblique Z-tenotomy. The criteria for surgical success were horizontal deviation at primary gaze of </=10(Delta), A pattern of </=8(Delta), and SOOA of </=1.0.

RESULTS

The study group included 28 patients with a mean age of 13.4 years. Thirteen (46.4%) had A-pattern esotropia; 15 (53.6%) had A-pattern exotropia. Fifteen (50%) had undergone previous surgery. The success rate for the whole group was 60.7%. There was no statistically significant difference in success rate between patients with esotropia (53.8%) or exotropia (66.7%) (p = 0.48) or between patients in whom the combined procedure was the primary (71.4%) or secondary (50.0%) treatment (p = 0.246). Measurements of horizontal strabismus remained stable throughout follow-up in the esotropia group but were unpredictable in the exotropia group.

CONCLUSIONS

The success rate of combined horizontal deviation/A-pattern surgery is unaffected by type of horizontal deviation or prior surgery.

Prevalence of horizontal deviation pattern changes with measurements in extreme gazes

PURPOSE

To analyse the difference between measurement of A and V pattern strabismus at 25 degrees and extreme gaze position in esotropia (ET) and exotropia (XT).

METHODS

This prospective cross-section study included 27 patients with basic horizontal strabismus associated to any deviation pattern. Mean age was 11.88+/-9.17 (6-44) years. Exclusion criteria were amblyopia, intermittent XT, noncollaboration with the exam, previous strabismus surgery, craniofacial, or spinal abnormalities. The deviations were measured with prism cover test at 6 m. Measurements were carried out in primary position, upgaze (neck flexion of 25 degrees and maximum flexion) and downgaze (neck extension of 25 degrees and maximum extension). A goniometer with a bubble level controlled the neck position.

RESULTS

The most significant changes were in downgaze. The pattern size increased 4 prism dioptres (PD) or more in 56.25% of the V- and in 87.5% of the A-patterns. The mean increase was 8.00+/-6.04 PD (0-17 PD) for the A-pattern ET, 4.80+/-3.70 PD (0-10 PD) for the V-pattern XT, and 6.50+/-5.58 PD (0-15 PD) for the V-pattern XT. The only case of A-pattern XT increased 8 PD.

CONCLUSION

Our results suggest that measurements in extreme up and downgazes may uncover increased deviations in a significant proportion of cases. Further studies remain necessary to determine the relevance of these findings for strabismus correction.