Inferior oblique muscle overaction (IOOA) may be primary or secondary. The former occurs in 72% of congenital esotropia, 34% of accommodative esotropia, and 32% of intermittent exotropia [
A variety of procedures have been performed including recession, hang-back recession, myotomy, myectomy, anterior transposition, nasal transposition, denervation, and muscle fixation [
This retrospective study was conducted in Hacettepe University Medical School, Ophthalmology Department, Pediatric Ophthalmology and Strabismus Section. The study protocol was approved by the institutional review board. The procedures conformed with the tenets of the Declaration of Helsinki. The consecutive patients who had undergone the inferior oblique muscle weakening surgery (tenotomy, recession, or anteriorization) as a sole procedure between 2001 and 2012 and who had postoperative control examination and whose orthoptic evaluation could be performed completely were enrolled in the study. The exclusion criteria were described in Table
The exclusion criteria of the study.
Exclusion criteria | |
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(1) Restrictive strabismus | |
(2) Uncooperation during measurements | |
(3) Combined surgery of horizontal and/or vertical muscles aside |
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(4) History of trauma | |
(5) Neurological, genetic, or craniofacial abnormalities |
The amounts of IOOA were classified as +1 to +4. Diagnosis was based on evaluation of ocular misalignment in 9 diagnostic gaze positions, and Hess Lee screen tests if applicable. Ocular misalignment was measured with the prism cover test or Krimsky. The retrospective data collected included the diagnosis at presentation, pre- and postoperative horizontal and vertical deviations in primary position, presence or absence of fourth nerve palsy, type of the inferior oblique weakening surgery including tenotomy, recession, or anteriorization, previous surgery of horizontal muscles, pre- and postoperative degree of IOOA, and the effect of inferior oblique muscle weakening intervention on the amount of horizontal near and distance deviations in primary position.
The insertion of the inferior oblique muscle was placed at the temporal border of the inferior rectus muscle in anteriorization and generally 2 mm posterior to the lateral of inferior rectus muscle in the recession procedure. The type of surgery was determined according to the surgeon’s preference.
The main measures were the type of IOOA, pre- and postoperative amount of IOOA, and horizontal deviations in primary position.
Postoperatively, the subjects were examined at three months after surgery.
Data were analyzed using SPSS 15.0 for Windows (SPSS Inc., Chicago, IL). For normal distribution of quantitative data, independent samples
Sixty-six patients (30 males and 36 females) with a median age of 11 years (1–49) were enrolled in the study. The median age of males was 14 years (2–49) and the median age of females was 6.5 years (1–39) (
Of the 66 patients, 36 (54.5%) had secondary IOOA due to fourth nerve palsy and 30 (45.5%) had primary IOOA. The most commonly performed surgery was inferior oblique anteriorization in 48.5% (32 patients), followed by inferior oblique tenotomy in 43.9% (29 patients), and recession in 7.6% (5 patients). Of the 66 patients, 39 (59.1%) underwent unilateral and 27 (40.9%) bilateral surgery.
Of the 66 patients, 9 (13.6%) had undergone previous horizontal muscle surgeries.
The median amount of IOOA in patients reduced from +3 (1–4) to 0 (0–2) in patients with secondary IOOA and from +3 (2–4) to +1 (0–2) in patients with primary IOOA (
The amount of horizontal near, distance, and vertical deviations was significantly decreased (
The change of deviations after surgery in patients with inferior oblique overaction.
Type of IOOA | ||||||||
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Deviations | Primary |
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|
Secondary |
|
| ||
Preoperative |
Postoperative |
Preoperative |
Postoperative |
|||||
Horizontal near | 14 (2–50) | 10 (0–50) | − |
9 (0–50) | 0 (0–50) | − |
||
Horizontal distance | 12 (2–55) | 10 (0–55) | − |
|
7 (0–55) | 0 (0–50) | − |
|
Vertical | 9 (0–40) | 0 (0–20) |
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12 (4–40) | 0 (0–20) |
|
*Wilcoxon signed-rank test.
The amount of correction in deviations was shown in Table
The amount of change in deviations after the inferior oblique muscle weakening procedures.
Deviations | Type of IOOA |
|
| |
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Primary |
Secondary | |||
Horizontal near | 2 (0–14) | 4 (0–25) | −1.263 | 0.207 |
Horizontal distance | 2 (0–14) | 4 (0–30) | −0.482 | 0.630 |
Vertical | 4 (0–30) | 10 (0–30) | −2.825 |
|
*Mann-Whitney test.
Weakening surgery for IOOA either primary or secondary includes recession, disinsertion and myectomy, tenotomy, marginal myotomy, and anteriorization. The aim of all these surgeries is to release IOOA and reduce related vertical deviations. The inferior oblique muscle is an abductor and its weakening might induce esoshift. In light of this basic information, in spite of the variability of the results, our starting point was the following question in the present study: could we have an estimation about the effect of the inferior oblique muscle weakening procedure on the magnitude of horizontal deviations and if it was possible to quantify it because if we can predict its effect on horizontal alignment, we can have the possibility to adjust our numbers for horizontal surgeries. There is few data in the literature about horizontal aligning effect of oblique muscle surgeries.
Souza-Dias [
Stager et al. [
All aforementioned studies had largely examined and analyzed the vertical effects of inferior oblique muscle weakening surgeries and related possible complications. However, their effects on horizontal deviations have not been described in detail. In this paper, we described our findings in a series of patients who underwent weakening procedure as a sole intervention and whose horizontal deviations were believed to have been ameliorated and found that weakening of inferior oblique muscle had significant effect on horizontal deviations. Although recession, anteriorization, and disinsertion were thought to have different effects on the horizontal alignment on primary position in regard of different axis of action, we did not found any difference between different types of surgery in terms of horizontal deviation correcting effect. The present data confirmed in brief that weakening of inferior oblique muscle may act as a horizontal deviation correcting procedure and may reduce the amount of horizontal misalignment.
It was not clear that the larger the preoperative horizontal deviations, the greater the amount of correction was obtained postoperatively. We found that the postoperative reduction of horizontal deviation was not related with preoperative amount of horizontal near and vertical deviations but it was influenced by preoperative amount of horizontal distance deviation. However, the reason for this relationship remained unexplained. The weakening caused an esoshift in primary position, which may be an expectable result in regard of inferior oblique muscle’s functions.
This study needs to be viewed in light of the following limitations: small number of cases, lack of control group, retrospective nature, and short-term followup. The presence of a previous horizontal muscle surgery may have an indirect long-term effect and may prohibit the evaluation of the pure effect of inferior oblique muscle weakening on horizontal deviations. Furthermore, the binocular status of the patients was not mentioned and described in the study and it may be a main topic for another study. However, weakening of inferior oblique muscle had shown promising results in correction of horizontal deviations. The question arises whether the effect of weakening on horizontal deviation may be predicted and quantified. This presumption would not be possible and realistic, because scaling of the surgical amount is always challenging for selected strabismus surgeries, in regard of the difficulty of the standardization of all steps; so the results of surgery may be surgeon specific and not generalizable, even not relevant because the median amount of diopter change was small (
In conclusion, when planning and performing a strabismus surgery which targets weakening of the inferior oblique muscle, it is important to have a thorough knowledge of its possible effects on horizontal deviations. Even if it is performed as a sole procedure, inferior oblique weakening, whatever the type of procedure is, may affect the horizontal alignment in primary position and may influence the surgical numbers for future horizontal muscle surgeries in so much that the numbers may need to be decreased particularly for exodeviations. This influence should be borne in mind.