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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 20  |  Issue : 2  |  Page : 88-94

Surgical outcomes of inferior oblique muscle weakening procedures for eliminating inferior oblique muscle overaction: a prospective randomized study


1 Department of Ophthalmology, Faculty of Medicine, Al-Azhar University, Assiut, Egypt
2 Department of Ophthalmology, Sohag Faculty of Medicine, Sohag, Egypt

Date of Submission05-Nov-2018
Date of Acceptance24-Mar-2019
Date of Web Publication24-Jul-2019

Correspondence Address:
Amr Mounir
Department of Ophthalmology, Sohag Faculty of Medicine, Almohafza Street, Sohag City 82511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/DJO.DJO_56_18

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  Abstract 


Purpose The aim of this study was to evaluate the outcomes of weakening surgical procedures for eliminating inferior oblique muscle overaction (IOOA).
Patients and methods A prospective randomized interventional study was performed on 20 eyes of 12 patients with IOOA. The eyes were classified randomly into three groups. The first group included six eyes treated with inferior oblique (IO) myotomy. The second group included eight eyes treated with IO myectomy. The third group included six eyes treated with IO muscle recession. The ductions, versions, and degree of IOOA were analyzed in all patients before and after surgery. Patients were included in the study only if they achieved a minimal follow-up period of 3 months.
Results Orthotropia was achieved in 13 (65%) eyes: three (15%) eyes in IO myotomy group, five (25%) eyes in IO myectomy group, and five (25%) eyes in IO recession group. One (5%) eye of IO myotomy group showed residual degree of IOOA. Underaction of IO occurred in one (5%) eye of IO myectomy and recurrence occurred in five (25%) eyes of all groups.
Conclusion Recession is the most effective procedure to eliminate IOOA, whereas myectomy at insertion is the second most effective procedure and myotomy is the least effective procedure.

Keywords: inferior oblique overaction, inferior oblique recession, myectomy, myotomy


How to cite this article:
Mohamed AK, Yousef HS, Mounir A. Surgical outcomes of inferior oblique muscle weakening procedures for eliminating inferior oblique muscle overaction: a prospective randomized study. Delta J Ophthalmol 2019;20:88-94

How to cite this URL:
Mohamed AK, Yousef HS, Mounir A. Surgical outcomes of inferior oblique muscle weakening procedures for eliminating inferior oblique muscle overaction: a prospective randomized study. Delta J Ophthalmol [serial online] 2019 [cited 2019 Sep 23];20:88-94. Available from: http://www.djo.eg.net/text.asp?2019/20/2/88/263415




  Introduction Top


Inferior oblique muscle overaction (IOOA) may be one of two types whether primary or secondary. The primary type occurs in 72% of congenital esotropia cases, 34% of accommodative esotropia cases, and 32% of intermittent exotropia cases [1]. Primary IOOA is usually bilateral but may be asymmetrical [2]. Secondary IOOA may be owing to ipsilateral superior oblique paresis or contralateral superior rectus paresis. Clinically IOOA presents by overelevation on adduction, upshot on adduction, V-pattern strabismus, hypertropia in primary position, and compensatory head posture in secondary IOOA owing to superior oblique paresis [3]. IOOA is the main cause of A and V patterns owing to dysfunction of the oblique muscle, and in these cases, surgical treatment is recommended [4].

Surgery for IOOA is indicated when IOOA and strabismus interfere with fusion or cause a cosmetic problem. Indications for these surgeries, whether primary or secondary, are to correct hypertropia, diplopia, binocular vision defect in the field of adduction, torticollis, and lastly to improve the cosmetic appearance [5].

The inferior oblique (IO) may be weakened effectively by graded recession/anteriorization, disinsertion, or myectomy, but graded recession/anteriorization and myectomy are the most commonly performed procedures worldwide [6]. Anterior transposition of IO is another different procedure for correcting IOOA. This procedure is effective in treatment of IOOA with coexisting dissociated vertical deviation [7].

The aim of the present study was to evaluate the outcomes of weakening surgical procedures for eliminating IOOA.


  Patients and methods Top


A prospective randomized study was performed on 20 eyes of 12 patients with primary IOOA from January 2016 to August 2016. All patients’ guardians signed a written informed consent to participate in the study, and the study was approved by Al-Azhar Assiut University Human Research Ethical Committee. The study was performed in agreement with the Declaration of Helsinki.

Inclusion criteria

The following were the inclusion criteria:
  1. Patients with age range between 4 and 15 years.
  2. Patients presenting with primary IOOA.
  3. Unilateral or bilateral cases with overacting IO muscle.
  4. Patients who had not previously undergone any IO muscle weakening procedure.
  5. Cases that required additional horizontal muscle surgery in addition to the IO muscle surgery.


Exclusion criteria

The following were the exclusion criteria:
  1. Uncooperative patients.
  2. Paralytic squint.
  3. Cases with secondary overaction (positive head tilt tests).
  4. Cases that required other vertical muscle surgery in addition to the IO muscle surgery.


All included cases were evaluated by prism cover test or Krimsky test. The amounts of IOOA were classified into +1 to +4. Diagnosis was performed by evaluation of ocular deviation in nine diagnostic gaze positions.

The eyes were classified randomly into three groups; randomization was performed by assigning random numbers from random number tables to the treatment options. The first group included six eyes treated with IO myotomy. The second group included eight eyes treated with IO myectomy. The third group included six eyes treated with IO muscle recession. The ductions, versions, and the degree of IOOA were analyzed in all patients before and after surgery.

Operative procedures

All of the surgical procedures were performed under general anesthesia using the following surgical technique:
  1. Forced duction test.
  2. A 270° conjunctival peritomy from 10 o’clock to 3 o’clock position was made for adequate muscle exposure.
  3. Surgery to correct horizontal deviation in primary position was independently done.


Inferior oblique muscle surgery

The lateral rectus muscle was hooked. A 4-0 silk traction suture was applied under the lateral rectus muscle. The suture was used to pull the eye up and in (superior and nasal) and was anchored to the head drape with a hemostat to expose the posterior temporal aspect of the globe. The eye should be rotated to an extreme superior-nasal position. This was followed by placing a hook along the inferior border of the lateral rectus muscle to expose the IO muscle, and then another hook was inserted directly against the sclera hooking it. Once the posterior border of the IO was identified by direct visualization, another hook was placed just behind the posterior border and rotated to hook the entire muscle.

The IO muscle was clearly exposed, isolated, and treated according to the used technique, which included the following.

Myotomy

An IO myotomy was performed between the nerve to the IO muscle and the insertion of the muscle. After muscle crushing with one or two hemostats, transverse surgical sectioning of the muscle was performed. Suture ligatures or cautery could be used for hemostasis.

Myectomy

An IO myectomy included removal of a section of the muscle to reduce the tendency of the myotomized ends to reunite. Two hemostats were used, as with the myotomy, except that a space of 5 mm or more was maintained between the hemostats, so that the segment of the muscle between the hemostats can be removed.

Recession

The IO muscle was recessed 8 mm by a double-armed 6/0 vicryl suture which was placed within the insertion of the IO with a locked bite at the anterior and posterior borders. The muscle was sectioned from the globe and recessed 8 mm by placing the anterior suture 4 mm lateral to the lateral insertion of the inferior rectus muscle and the posterior suture 3 mm more laterally [8].

Postoperative evaluation was done on the first day postoperatively and at 1 week, 1 month, 3 months, and 6 months. It included the following:
  1. Angle of deviation.
  2. Complications (infection, diplopia, retinal tear, and anterior segment ischemia).
  3. Residual overaction of the IO muscle.
  4. Residual angle of deviation, measured by the Krimsky method.
  5. Other complications (granuloma, allergic reaction, conjunctival scarring, conjunctival inclusion cyst, and signs of adherent syndrome).



  Results Top


The study included six males and six females (eight cases of bilateral IO overaction and four cases of unilateral IO overaction). Preoperative data are summarized in [Table 1] and [Table 2], [Figure 1].
Table 1 Patients’ descriptive data

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Table 2 Percentage of degree of inferior oblique overaction

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Figure 1 Preoperative types of horizontal deviation.

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Horizontal esotropia ranged from 15° to 40°, whereas IOOA ranged from +2 to +4 ([Table 2]), and V-pattern was present in four patients ranging from 5° to 15°.

The preoperative cycloplegic refraction was myopia of spherical equivalent of −1.75 D in one patient to hyperopia of spherical equivalent between +1 and +8 D in seven patients. Four patients were emmetrope. Three patients used spectacle correction for more than 4 weeks before surgery. No patients in this study received miotics, orthoptics, or prisms.

The operative technique used in this study was combined recession-resection for horizontal deviation, with myectomy, myotomy, or recession of the IO muscle. Frequency and percentage of surgical procedures are summarized in [Table 3] and [Figure 2].
Table 3 Frequency and percentage of surgical procedures

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Figure 2 Percentage of surgical procedures.

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The postoperative results of all the patients occurred in the four categories:
  1. Normal IO action.
  2. IO residual overaction.
  3. IO underaction.
  4. IO recurrence.


The success rate was highest in IO recession group (83.3%) with significant improvement at the first and third month postoperatively (P=0.05), and the success rate was least in IO myotomy group (50%) with no significant improvement. The recurrence rate was highest in the IO myotomy group (33.3%) and least in the IO recession group (16.7%), whereas underaction was observed only in IO myectomy group (12.5%) ([Table 4]).
Table 4 Postoperative results

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The postoperative results were summarized in [Table 4],[Table 5],[Table 6],[Table 7] and [Figure 3]. [Figure 4] illustrates the preoperative and postoperative findings in a case of bilateral IO recession for a case of bilateral IO overaction with accommodative esotropia.
Table 5 Inferior oblique muscle action following the procedures

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Table 6 Postoperative inferior oblique muscle function

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Table 7 Preoperative and postoperative A–V pattern

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Figure 3 Postoperative results.

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Figure 4 The preoprative and postoperative photos of a case of bilateral IOOA with accommodative esotropia with improvement of IOOA after bilateral IO recession. A written consent was taken from the patient’s guardian for taking these photos. (a) Preoperative primary position. (b) Preoperative Lt. IO testing. (c) Preoperative Rt. IO testing. (d) Postoperative primary position. (e) Postoperative Lt. IO testing. (f) Postoperative Rt. IO testing. (g) Postoperative primary position with glasses. IO, inferior oblique; IOOA, inferior oblique overaction; Lt, left; Rt, right.

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The postoperative complications ([Table 8]) included granuloma (15%), conjunctival inclusion cyst (5%), and conjunctival scarring (15%). Residual IOOA (±1) occurred in one (5%) case, recurrence in five (25%) cases, and underaction in one (5%) case. Residual esodeviation (under correction) occurred in 20% of the cases. V-pattern successfully improved in four (66.7%) cases, whereas remained in two (33.3%) cases ([Table 7]). Adherence syndromes had not been observed in any patient in this study.
Table 8 Postoperative complications

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  Discussion Top


Weakening of the IOOA has been recommended in cases with clinically significant presentation, with both myectomy and muscle recession being widely performed [9]. The advantages of IO myectomy over recession are easier technique, shorter operative time, no fear of scleral perforation, or vortex vein damage and less liability of permanent IO paralysis [10].

In the present study, 20 eyes of 12 patients with primary IOOA were examined and operated upon. The success was highest in IO recession group with significant improvement at the first and third month. These results are similar to Parks [11], who found that recession was superior to myectomy as it showed lower recurrence rate and no adherence syndrome. His recurrence rate was 15.3% in recession and 37.4% in myectomy procedure. In the current study, the recurrence rate of myectomy was 25% which was far less than the reported 37.4% in Parks’ study taking into consideration the difference in number of cases between the two studies. In addition, adherence syndrome was not observed. Remaining IO overaction was observed in only 16.7% of patients who underwent myotomy and was not observed in patients who underwent myectomy.

IO underaction following myectomy is the feared complication. In the present study, IO underaction was observed in only 12.5% of patients after 4 months or more of follow-up, and these were not a complete paralysis. The study by Chang and Yang [12] on IOOA found that myectomy at the insertion site of the IO muscle resulted in improvement of 95.5%, recurrence of 2.7%, and residual IOOA in 1.8%. These results were far different from the current study.

Taha et al. [13] evaluated the efficacy of IO suspension recession in cases of V-pattern strabismus and primary IOOA and compared it with standard graded recession technique. They found that the results of the standard recession technique were significantly superior.

In the present study, myectomy at the insertion of the IO muscle had been done on eight patients: three cases with second degree of overaction and the other five cases with third degree of overaction. At the first postoperative day, the eyes with myectomy showed underaction of the IO muscle, which was probably owing to nonattachment of the IO muscle to the globe. In addition, the residual overaction shown from the first postoperative month meant that the IO muscle had reattached to the globe. At four months and more of follow-up after operation, there was one case with underaction which had been second degree of overaction before surgery and two cases showed recurrence which had been third degree of overaction before surgery and became first degree of overaction. Myectomy at the insertion of the IO muscle resulted in a 25% recurrence of overaction, and 62.5% perfect result. IO underaction following myectomy is the feared complication. Myectomy of the IO resulted in 12.5% of underaction.

Myotomy has many advantages owing to its unlikelihood of permanent IO paralysis but its weakening effect is inferior to the other weakening procedures. IO myectomy is a favorable producer that is easier to be performed, of shorter operation time, no liability of scleral perforation or vortex vein damage, and unlikelihood of permanent IO paralysis, meaning less complicated than recession [14]. In contrary to these results, Ehrt et al. [15] and Ali et al. [16] had a higher incidence of normalizing IO function. This controversy and horizontal misalignment can be explained on the basis of the study done by El Hilaly and Saeed [17] which showed the effect of IO weakening surgery on the primary position horizontal alignment. As known that the IO is an abductor of the eye in addition to its main action which is elevation and extortion, it seems logical that surgical weakening of that muscle would result in eso-shift in the primary position.

Stager and Parks [18] suggested that there is little or no effect of IO weakening on the primary position of horizontal alignment. In addition, Knapp [19] reported that in patients with large horizontal deviations in whom he performed the vertical muscle surgery first, it induced very minimal change in the angle of the horizontal deviation. Jampel [20] deduced from his studies that the horizontal pull rendered by the IO changes as the eye moves along the horizontal and the vertical planes and in the primary position.

Kraft and Scott [21] studied the surgical outcome of patients with V-pattern esotropia regarding the postoperative primary position horizontal alignment, and they found esotropia more in patients who undergo IO surgery. This was a trial to evaluate the effect of IO weakening procedures on the angle of V-pattern esotropia, when the IO weakening was done concurrently with bilateral medial rectus recession. Further confirmation for this controversy was observed in the present study, in which no effect of IO weakening was noticed on the primary position of horizontal alignment.


  Conclusion Top


Recession is the most effective procedure to eliminate IOOA, whereas myectomy at insertion is the second most effective procedure and myotomy is the least effective procedure. IO myectomy is a favorable producer that is easier to perform and takes shorter time than recession.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Wilson ME, Parks MM. Primary inferior oblique overaction in congenital esotropia, accommodative esotropia, and intermittent exotropia. Ophthalmology 1989; 96:950–955; discussion 956-957.  Back to cited text no. 1
    
2.
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Chang BL, Yang SW. Inferior oblique overaction. Korean J Opthalmol 1988; 2:77–81.  Back to cited text no. 12
    
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Taha RH, El Gendy HA, Kamal MA, El Guindy FM. Suspension recession of inferior oblique versus graded recession technique in V-pattern strabismus with primary inferior oblique overaction. Delta J Ophthalmol 2017; 18:176–181.  Back to cited text no. 13
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17.
El Hilaly H, Saeed H. Effect of concurrent inferior oblique weakening during horizontal muscle surgery for V pattern exotropia on the primary position horizontal alignment. Bull Ophthalmol Soc Egypt 2000; 93:891–895.  Back to cited text no. 17
    
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Stager DR, Parks MM. Inferior oblique weakening procedures, Effect on primary position horizontal alignment. Arch Ophthalmol 1973; 90:15–16.  Back to cited text no. 18
    
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Knapp P. Surgical treatment of strabismus. Surgical treatment of strabismus. Allen JH, ed. Strabismus symposium 11. St Louis: CV Mosby Co. 1958. 377–390.  Back to cited text no. 19
    
20.
Jampel RS. The fundamental principle of the action of the obliques ocular muscles Am J Ophthalmol 1970; 69:623–638.  Back to cited text no. 20
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]



 

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