Anteriorization of inferior oblique muscle in management of dissociated vertical deviation with or without inferior oblique muscle overaction

Mahmoud M Saleh

doi:10.4103/DJO.DJO_60_17

ORIGINAL ARTICLE

Year : 2018 | Volume : 19 | Issue : 1 | Page : 72-77

Anteriorization of inferior oblique muscle in management of dissociated vertical deviation with or without inferior oblique muscle overaction

Mahmoud M Saleh MD
Department of Ophthalmology, Al-Azhar University, Cairo, Egypt

Date of Submission	12-Sep-2017
Date of Acceptance	29-Nov-2017
Date of Web Publication	1-Feb-2018

Correspondence Address:
Mahmoud M Saleh
Department of Ophthalmology, Al-Azhar University, Cairo 11441
Egypt

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/DJO.DJO_60_17

Abstract

Purpose
The aim of this study was to evaluate and compare the effect of anterior temporal transposition of the inferior oblique (IO) muscle in the management of dissociated vertical deviation (DVD) whether associated with or without inferior oblique muscle overaction (IOOA).
Patients and methods
This study was carried out on 34 eyes (20 patients) with DVD of at least 10 prism diopters (Δ) in the involved eye. The patients were divided into two groups. Group I included 17 eyes of 11 patients having DVD with IOOA, and group II included 17 eyes of nine patients having DVD without IOOA. The IO muscle was approached through the conjunctiva and Tenon’s capsule by an inferior-temporal fornix incision. The size of preoperative and postoperative DVD, grade of the preoperative and postoperative IOOA, repeat surgeries, and complications were recorded and evaluated.
Results
The average correction of DVD in group I was 8.13 Δ (preoperative 16.53 Δ and postoperative 8.5 Δ, P<0.001) and 9.47 Δ in group II (preoperative 17.67 Δ and postoperative 8.2 Δ, P<0.001). The mean IOOA was corrected from +2.0±0.5 to +0.18±0.4 in group I (P<0.001). The mean follow-up period was 9.2±2.2 months in group I and 9.3±3.1 months in group II.
Conclusion
Anteriorization of the IO muscle was effective in correcting DVD with or without IOOA. Preoperative DVD equal to or less than 15 Δ had favorable outcome, but DVD more than 15 Δ had less favorable outcome.

Keywords: anterior temporal transposition of the inferior oblique muscle, dissociated vertical deviation, inferior oblique muscle overaction

How to cite this article:
Saleh MM. Anteriorization of inferior oblique muscle in management of dissociated vertical deviation with or without inferior oblique muscle overaction. Delta J Ophthalmol 2018;19:72-7

How to cite this URL:
Saleh MM. Anteriorization of inferior oblique muscle in management of dissociated vertical deviation with or without inferior oblique muscle overaction. Delta J Ophthalmol [serial online] 2018 [cited 2018 Dec 10];19:72-7. Available from: http://www.djo.eg.net/text.asp?2018/19/1/72/224573

Introduction

Dissociated vertical deviation (DVD) is a slow, disconjugate hypertropic deviation of a nonfixing eye. It is usually bilateral, asymmetrical, and often associated with congenital esotropia. The deviating eye elevates, abducts, and excyclotorts. This type of strabismus is often variable, making measurement and quantification difficult [1]. In addition to DVD, inferior oblique overaction (IOOA) is also responsible for excessive elevation of one or both eyes but only in adduction [2]. To differentiate between DVD and IOOA, in DVD, neither eye refixates with an upward movement, whether adducted, abducted, or in primary position. In addition, A-V pattern horizontal deviation is common with overacting inferior oblique (IO) muscles but not with DVD. DVD may occur spontaneously (manifest DVD) or when one eye is occluded (latent DVD). Surgery is indicated in latent DVD when vertical deviation occurs spontaneously, is frequent, or cosmetically significant. The measurement of DVD can be complex, even for the experienced examiner [3]. Some examiners use the estimation technique, on the grading scale of 1–4. DVD is graded as 1 in small angle less than 5 Δ, with excellent control. A DVD is graded as 2 in a small angle with poorer control. Grade 3 indicates poorly controlled DVD greater than 10 Δ. A DVD is graded as 4 if manifest and greater than 15 Δ. This technique is most useful in infants and in uncooperative patients [1]. The other measurement technique is an adapted prism and alternate cover test with each eye fixing. The examiner uses a base-down prism in front of the upwardly deviating eye while it is behind an occluder. The occluder is then switched to the fixating lower eye. The base-down prism power is adjusted until the deviating eye shows no downward movement to refixate [3].

Several different procedures have been used with varying success to surgically manage DVD. In the past, bilateral large (symmetrical or asymmetrical) inferior rectus resections were advocated, but, in recent years, this procedure has been abandoned by many surgeons [4],[5],[6]. Currently, two methods have been preferred, particularly when both DVD and IOOA are present, and these are anterior transposition of the IO muscle (anteriorization) and myectomy of the IO muscle [4],[6],[7].

Anteriorization of the IO muscle transforms the IO from an extorter into an intorter and from an elevator to a depressor. The anteriorization can be used to eliminate or reduce severe excyclotorsion and overelevation in adduction combined with DVD [8],[9],[10].

The objective of this study was to compare the effect and results of anterior temporal transposition of the inferior oblique muscle (ATIO) in patients who had DVD with IOOA compared with patients having DVD without IOOA.

Patients and methods

This prospective study was approved by the Ethics Committee of the Department of Ophthalmology, Faculty of Medicine, Al-Azhar University. Written informed consent was obtained from all patients or their legal guardians after full explanation of the procedure. The study included 20 patients (34 eyes) with DVD of 10 or more prism diopters (Δ) in one or both eyes. The patients were divided into two groups. Group I (17 eyes of 11 patients) had DVD with IOOA, and group II (17 eyes of nine patients) had DVD without IOOA. The selection criteria for inclusion in the study were the patients with manifest or latent DVD who were indicated for surgery (vertical deviation occurs spontaneously, frequently or cosmetically significant), with or without IOOA. The patients who had paretic or restrictive strabismus, any prior surgery for the oblique muscle, vertical rectus muscle, or concurrent vertical off-setting of the horizontal rectus muscles as well as patients with any systemic disorder or syndrome that might have affected extraocular muscles were not included in the study.

High level of cooperation was needed for optimum preoperative and postoperative measurements, and so uncooperative patients were also excluded. DVD was measured by using a prism and an alternate cover test in which the eyes, in primary position, are fixing at an adjustable target at a distance of 6 m and have full refractive corrections; when these are worn, any concurrent horizontal deviation was neutralized using a horizontal prism. Subsequently, DVD in the other eye was measured in the same way. True hypertropia was measured in primary eye position and in side gazes to distinguish between IOOA and DVD. True hypertropia or hypotropia was measured in side gaze with base-down prism in front of the adducted eye. The amount of base-down prism needed to neutralize any hypotropic shift of the abducted eye represented true hypertropia or hypotropia. Any additional base-down prism needed to neutralize the hyperdeviation of the adducted eye represented DVD of the adducted eye [6]. V pattern was measured as the difference between horizontal deviations in up and down gazes. Oblique muscle function was estimated on a grading scale of 1+ to 4+ (overaction) based on eye movements in an upward, a downward, and a side gaze. Grade 1+ represented 1 mm of higher elevation of the adducting eye in gaze up and to the side. Grade 4+ indicated 4 mm of higher elevation.

Surgical procedure

The IO muscle was approached through the conjunctiva and Tenon’s capsule by an inferior-temporal fornix incision. During the procedure, the lateral rectus muscle was isolated by a muscle hook. The IO muscle was exposed by placing a small Steven’s hook along the inferior border of the lateral rectus muscle and a large Von Graefe hook was placed directly against the sclera to be inserted posteriorly under the IO muscle. The Von Graefe hook was properly positioned perpendicular to the IO muscle fibers under the entire width of the IO muscle. Raising the hook allowed visualization of the area between the IO muscle and the sclera. Once the posterior border of the IO muscle was identified by direct visualization, a Steven’s hook was placed behind the posterior border. The IO muscle was isolated from its fascial attachments both anteriorly and posteriorly. A 6-0 suture (Vicryl) was passed through the muscle. The IO muscle was thus secured with a double-arm suture and was then disinserted with blunt Westcott scissors. After the IO muscle was disinserted, the muscle was reattached to the sclera by using the crossed-swords technique so that the new insertion lay lateral to and collinear with the inferior rectus muscle insertion. The IO muscle was then inspected to ensure that no residual fibers remained that had not been anteriorly transposed. The conjunctiva was closed with 6-0 suture ([Figure 1]).

Figure 1: RT IO anteriorization (A) The IO muscle isolated from its fascial attachments (B) A 6–0 suture (Vicryl) through the muscle (C) IO disinserted with the blunt Westcott scissors (D, E, F) IO muscle reattached to the sclera by using the crossed-swords technique so that the new insertion lay lateral to and collinear with the inferior rectus muscle insertion.

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Statistical analysis

The results were evaluated and analyzed using the computer program SPSS (IBM Corp, Armonk, New York, USA). Statistical significance was tested using paired t-test and Wilcoxon test, with a P value less than 0.05 considered statistically significant.

Results

In group I (DVD with IOOA), the patients’ age ranged from 7 to 30 years, with a mean of 21.6±4.6 years. Six (54%) patients were females and five (46%) patients were males. Six patients had bilateral DVD (54%). Preoperatively DVD angle measured between 10 and 30 Δ (mean: 16.53±6.1 Δ) in primary position (70% of eyes had DVD ≤15 Δ, whereas in the remaining eyes DVD was ˃15 Δ; 30%). Postoperatively, DVD angle measured between 2 and 13 Δ (mean: 8.5±4.7 Δ).

All patients in group I had preoperative IOOA ([Table 1] and [Figure 2]). The mean IOOA decreased from +2.0±0.5 preoperatively to +0.18±0.4 postoperatively. This improvement of IOOA was statistically significant (P<0.001). Persistent IOOA (+1) was observed postoperatively in only one eye whereas one eye developed postoperative IO underaction (−1).

Table 1: Grading of inferior oblique muscle overaction in group I

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Figure 2: Female patient with RT DVD 15Δ and IOOA +3, (A) Eyes in primary position without covering (B) Gaze to the right with no overaction of IO of LT eye (C) Gaze to LT with the appearance of RT IOOA (D) RT eye under transparent occlusion with the appearance of DVD.

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In group I, ATIO was done isolated in six patients and combined with horizontal muscle surgery in five patients. All patients who underwent combined ATIO and horizontal muscle surgery were esotropic. They underwent ATIO combined with bimedial rectus recession (average: 5.0±0.5 mm), which resulted in improvement of their esotropia from 35±3.07 Δ preoperatively to 5.5±4.0 Δ postoperatively.

In group II (DVD without IOOA, [Figure 3]), the patients’ age ranged from 9 to 31 years, with a mean of 15.3±3.8 years. Five (55%) patients were females and four (45%) patients were males. Five patients had bilateral DVD. Preoperatively DVD angle measured between 10 and 30 Δ (mean: 17.67±5.8 Δ). Eleven eyes had DVD ≤15 Δ (65%) and the rest had DVD ˃15 Δ (35%). Postoperatively, the DVD angle measured between 0 and 12 Δ (mean: 8.2±3.04 Δ).

Figure 3: Female patient with RT DVD 15Δ without IOOA (A) Eyes in primary position without covering (B) Gaze to the right with no overaction of IO of LT eye (C) Gaze to LT with no overaction of IO of RT eye (D) RT eye under transparent occlusion with the appearance of DVD.

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In group II, ATIO as isolated procedure was done in four patients and with horizontal muscle surgery in five patients. In patients who underwent combined ATIO and horizontal muscle surgery, three patients were esotropic with an average preoperative deviation of 30.7±5.5 Δ and two patients had 35.9±5.4 Δ exotropia. ATIO combined with bimedial recession (average: 5.1±0.4 mm) was done to esotropic patients, which resulted in an average postoperative deviation of 3±2 Δ esotropia. The exotropic patients underwent combined ATIO with 7.5 mm bilateral lateral rectus recession that resulted in 5 Δ exotropia, postoperatively.

Preoperatively, four patients, two in each group, had no fusion with Worth’s four dot test. All other patients had different grades of stereopsis ranging from 40 to 800 arc sec.

Assessment of postoperative deviation in terms of the mean value of prism diopters showed that the surgical technique was successful because the differences between preoperative and postoperative values were significant ([Figure 4]).

Figure 4: Pre and postoperative deviation in terms of the mean value of prism dioptres Δ for both groups..

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In both groups, all eyes (100%) with preoperative DVD less than 15 Δ (70% of eyes in group I and 65% of eyes in group II) achieved an excellent outcome (DVD 0–5 Δ). In group I, 30% of eyes before surgery had DVD greater than 15 Δ, among them, 45% had a good outcome (DVD 6–9 Δ) and 56% had a fair outcome (DVD 10–13 Δ), postoperatively. In group II, in eyes that had preoperative DVD greater than 15 Δ (35%), 40% had a good outcome (DVD 6–9 Δ) and 60% had a fair outcome (DVD 9–12 Δ), postoperatively. The mean follow-up was 9.2±2.2 months in group I and 9.3±3.1 months in group II.

Discussion

DVD does not respond to orthoptic treatments and cannot be cured by itself. Therefore, the only cure for DVD is surgery [11],[12]. Several authors have evaluated the effectiveness of anteriorization of the IO muscle (ATIO) for management of DVD. These studies [2],[3],[4],[5],[6],[7],[8],[9],[10] have shown that ATIO is effective in controlling DVD in most cases and that it is more effective in treatment of DVD in the presence of IOOA. The ATIO procedure makes the IO muscle tonic depressor, so it can be used also for management of DVD without IOOA [13]. Because DVD is mostly seen with horizontal deviation, operating on the superior rectus and inferior rectus muscles, in addition to the horizontal muscles, can lead to anterior segment ischemia. A change in the palpebral fissure can be another adverse effect of the operation. On the contrary, if DVD occurs with IOOA, operating on the vertical muscles alone cannot resolve both problems. Elliott and Nankin [14] used ATIO to correct IOOA and discovered that it reduced not only IOOA but also the amount of DVD. According to the study of Mims and Wood [15], recession with anteriorization of the IO 2 mm away from the insertion of the inferior rectus can prevent the development of DVD. Engman et al. [16] compared standard and graded ATIO for the correction of DVD and noticed no major difference statistically. Snir et al. [17] reported their success in IO bilateral anteriorization with monocular graded IO recession in patients with nonsymmetrical DVD with IOOA. Quinn et al. [18] mentioned that adding 7 mm resection of the IO muscle to the standard ATIO procedure offers no advantage over the standard method. Stager [19] showed that, after ATIO, the neurofibrovascular bundle of the IO muscle acts as an ancillary origin and will transform the IO from an elevator to an antielevator.

The present study was designed to compare the results of anterior transposition of the IO muscle in patients who had DVD with IOOA with those of patients who had DVD without IOOA.

In group I, ATIO improved vertical deviation up to 20 Δ in primary position with marked improvement of IOOA. Two cases developed residual vertical deviation of more than 10 Δ (preoperatively were 25–30 Δ), which needed superior rectus recession. Guemes and Wright [20] suggested that unilateral anterior transposition procedure resulted in a mean reduction in the vertical deviation of 18 Δ. Weakening of the IO muscle produces 5–10 Δ reduction in hyperdeviation in the primary position and up to 20 Δ reduction in hyperdeviation in the field of action of this muscle [20].

In the present study, unilateral anterior transposition of IO had been done in five cases in group I; two cases developed contralateral DVD. Apparent contralateral IOOA after unilateral IO muscle weakening procedures was because the procedures not only weaken the IO muscle but also modify, quantitatively and qualitatively, the field of action, so there is the limitation of elevation in abduction after anterior transposition and the concurring apparent IOOA in the contralateral eye [21],[22].

Limited elevation in abduction developed after surgery in two eyes in group I and in one eye in group II. Kushner [21] had shown that the limited elevation in abduction, a complication of ATIO, occurs when the transposition of the IO muscle anterior to the inferior rectus muscle insertion is greater than 1 mm. This complication, which results in either a Y or V pattern, is more likely to happen if the IO insertion is spread out when being reattached to the globe. ATIO converts the posterior fibers of that muscle segment to a tonic depressor in the primary position and an antielevator limiting upgaze to 30–35° [9],[23]. After ATIO, the normal increased innervation of the IO muscle on supraduction produces a powerful force vector directed inferiorly, an effect termed antielevating [24]. This antielevating force can produce overaction of the contralateral elevators in adduction that mimics recurrent or new overaction of the IO muscle of the other eye [25],[26].

In group II, ATIO improved vertical deviation up to 20 Δ in primary position. Three cases developed residual vertical deviation of more than 10 Δ (preoperative DVD angle was 25–30 Δ).

In the current study, in both groups, preoperative DVD equal to or less than 15 Δ had an excellent outcome in all patients. Eyes that had preoperative DVD of more than 15 Δ had less favorable outcome. Standard anterior transposition of the IO muscles appears to be less effective in patients with larger amounts of DVD according to the research done by Engman et al. [16].

In the current research, ATIO decreased the amount of DVD in both groups, which is statistically significant. Statistical analysis of the results in both groups showed that there was no major difference between the two groups. Therefore, using ATIO in DVD with and without IOOA was an effective method. In addition, we observed the effect of ATIO in correcting different amounts of IOOA in group I and realized that there was a statistically significant difference.

The results of this study should be understood within the domain of representing a relatively small sample size owing to the specificity of the inclusion and exclusion criteria. However, despite this limitation, this study revealed important findings for the management of patients with DVD.

Conclusion

The IO anteriorization was effective in correcting DVD of both groups and effective for treating IOOA associated with DVD. Preoperative DVD equal to or less than 15 Δ had favorable outcome but DVD more than 15 Δ had less favorable outcome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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