Efficacy of transposition of plicated medial rectus muscles in the treatment of A- or V- pattern exotropia (An Egyptian comparative study)

Abstract

Purpose:

To report the effectiveness of bimedial plication and vertical transposition for correction of exotropia associated with A- or V-pattern and compare it with bimedial resection and vertical transposition.

Methods:

We retrospectively reviewed the results of surgery in patients who underwent bimedial plication (group I) versus bimedial resection (group II) with vertical offset to correct both exotropia and pattern deviation not secondary to oblique overaction in the period between January 2021 and January 2023. The results of both groups were compared. Success was considered when pattern deviation was ≤8 prism diopters (PD) and horizontal deviation was within 10 PD of orthophoria at 6 months postoperatively.

Results:

The mean preoperative angle of exotropia in PD was 40.6 ± 7.2 in group I and 41.1 ± 7.5 in group II (P = 0.8). At 6 months postoperatively, they achieved angle of 4.6 ± 4.1 and 2.5 ± 4.5 PD, respectively (no significant difference between both groups; P = 0.19). The mean preoperative pattern deviation was 21.3 ± 3.7 PD in group I and 21.6 ± 4.4 in group II. Postoperative pattern collapse was 16.7 ± 5.6 and 16.6 ± 4.1, respectively. The percentage of success in pattern collapse was 90.6% in group I and 84.4% in group II (no significant difference between the groups; P = .71).

Conclusion:

Vertical transposition with plication of medial recti is a safe, effective, and rapid technique for correction of cases of A- or V-pattern exotropia not associated with oblique overaction. Results were not significantly different from resection/vertical transposition.

The amount of horizontal deviation in strabismic patients may differ in upgaze and downgaze apart from the primary position. This difference is called A- and V-patterns or alphabetical patterns.[1] A-pattern is described when the difference in horizontal deviation between upgaze and downgaze is more than 10 PD, with more divergence in downgaze, while V-pattern is described when this difference is more than 15 PD, with more divergence in upgaze.[2] The reported prevalence of A- or V-patterns in patients with horizontal deviation ranges between 20% and 50% in different studies.[3]

Many theories were proposed to clarify the etiology of alphabetical patterns, like: oblique muscle overaction or palsy, nerve misdirection such as Duane syndrome, orbital factors as craniofacial abnormalities, heterotopia of muscle pulleys, extraocular muscles’ anomalies, and disruption of fusion.[4,5]

Intermittent exotropia is the most common type of exodeviation. It is a large phoria that can be controlled intermittently by fusional mechanisms and may later progress spontaneously into constant exotropia with loss of control. A- and V-patterns are seen in a large number of patients with typical intermittent exotropia.[1,6]

Detection of pattern deviation in cases of exotropia or horizontal deviation — in general — is very important before determining surgical intervention. Unrecognized patterns may lead to either postoperative over- or undercorrection or may necessitate additional surgeries to address suboptimal outcomes.[2]

The generally accepted surgical corrections of pattern strabismus include oblique muscle weakening when there is obvious oblique muscle overaction and horizontal muscle transposition when there is not.[7,8,9,10,11] However, both procedures can be done together in large patterns.[2] Other approaches include surgery on vertical recti (nasal or temporal horizontal displacement of insertions) and slanting of horizontal recti insertions.[12]

Many options are advocated for the correction of exotropia: unilateral recession resection, bilateral lateral rectus recession, or bimedial resection. A three or four-muscle surgery may be done in large-angle exotropia.[13] Muscle plication is an alternative surgical procedure to muscle resection, used to strengthen the muscle. It has the benefit of being potentially reversible as well as being better in preserving the anterior ciliary circulation; thus lowering the risk of anterior segment ischemia.[14,15] Plication also reduces the risk of a lost muscle, and it can be performed using adjustable-suture techniques.[16]

The combination of both vertical transposition and plication of the horizontal recti is one of the newer techniques used for the correction of cases with both vertical and horizontal strabismus (as elaborated in the discussion).[14,16] In this retrospective cohort study, we chose cases with unoperated exotropia — either constant or intermittent — associated with pattern deviation who underwent either medial rectus muscle plication and transposition or the standard technique in which resection is done instead of plication with either superior or inferior transposition according to the type of pattern (A or V). We hypothesized that this technique is as effective as bimedial resection and transposition. However, bimedial plication and transposition will offer advantages regarding safety, short operation time, as well as decreasing incidence of postoperative anterior segment ischemia.

Methods

Informed consent was taken from patients or their parents (for children less than 16 years old). All surgeries were performed at the Ophthalmology department of our hospital.

The medical records of patients diagnosed with A- or V-pattern exotropia with minimal or no oblique overaction, who underwent strabismus surgery between January 2021 and January 2023, were retrospectively reviewed. Only patients with constant or intermittent exotropia, with angle of deviation ≥30 and ≤55 PD who were not operated on before, were included. A-pattern exotropia was included when the difference in exodeviation between upgaze and downgaze was more than 10Δ, and V-pattern when this difference was more than 15Δ. Age ranged from 4 to 50 years old.

Patients with residual or consecutive exotropia, sensory exodeviation, oblique muscle overaction (≥ +2), anisometropia ≥ 5 of diopters, axial length < 22.5 or > 25 mm, associated dissociated vertical deviation (DVD), or less than 6 months’ follow-up were excluded.

Preoperative data collected included best corrected visual acuity in Snellen decimal, cycloplegic refraction (using 1% cyclopentolate chloride) with retinoscopy or autorefractometry, extraocular muscle movement, degree of ocular deviation in primary position at distance (6 meters) and at near (1/3 meter) by prism and alternating cover test, horizontal deviation at 1/3 meter (in upgaze and downgaze, about 25 degrees up and down, respectively, without glasses to avoid prismatic effect of spectacle correction), pattern deviation is the difference in horizontal deviation between up and downgazes, oblique muscle overaction grading from +1 to +4,[17] stereoacuity at near by Titmus test (with poor being >200 arcsec and moderate being between 80 and 100), slit lamp examination of the anterior segment, and fundus examination by indirect ophthalmoscope.

After matching all preoperative data based on age (in years), sex, BCVA, refraction, preoperative angle of exotropia, V-pattern and A-pattern, we divided patients in two groups, each group was further divided into two subgroups A and V referring to A- and V-patterns: (1) Group I (32 patients) underwent bilateral medial rectus plication and vertical transposition, (2) Group II (control group, 32 patients) underwent bimedial resection and vertical transposition. The degree of A- and V-pattern collapse (the difference between pre- and postoperative pattern deviation) was calculated at 1 month and 6 months postoperatively. Success was considered when the pattern deviation was ≤8 PD at 6 months postoperatively. Success in horizontal deviation was considered when deviation was 10 PD within orthophoria at 6 months postoperatively.

Surgical technique

All surgical procedures were performed under general anesthesia by the same surgeon (MG). A limbal-conjunctival incision was done. It is about 3 hours length with two horizontal releases at the end of the incision to make the opening wider. The medial rectus muscle was exposed and freed from the Tenon’s tissue to the planned distance for resection or plication.

For the plication [Fig. 1], one double-armed 6-0 Vicryl suture was passed through the center and both muscle edges at the desired distance from the muscle’s insertion and locked. Then, each suture was placed toward the site of transposition. For example, if we targeted to transpose the medial rectus a full-tendon-width superiorly, the inferior suture was passed under the medial rectus to the superior edge of the muscle insertion. The superior suture was passed partial thickness of the sclera, just anterior to the muscle insertion, with a vertical offset of about 8–10 mm. Then, the inferior suture was passed through the sclera approximately at the superior edge of the insertion. Both sutures were tied together, which resulted in a triangular fold in the muscle [Video 1].

Figure 1.

Medial rectus muscle plication and vertical transposition. (a) The medial rectus is stretched between the two muscle hooks. (b) A single double-armed 6-0 Vicryl suture was passed through the muscle center to the superior edge. (c) The suture was passed to the inferior edge after locking the superior one. (d) Picture after locking both sutures. (e) Inferior suture was passed through the sclera at the superior pole of muscle insertion, and the superior suture was passed through the sclera a full-tendon-width above the first scleral path. (f) Position of the muscle after tying the sutures. (g) Final appearance of the folded and transposed muscle

For the resection, two single-armed 6-0 Vicryl sutures were passed through both muscle edges at the desired distance from the muscle insertion and tied; then, the muscle was disinserted from the globe and resected just anterior to the previously-passed sutures. The muscle was then transposed and secured to the sclera at the desired position with partial-thickness scleral passes.

In the A-pattern group, medial recti were displaced upward (toward the apex of the pattern) by 5 mm if the difference between up and downgazes was 10–≤20 PD and 8–10 mm if >20 PD. In the V-pattern group, they were displaced downward by 5 mm if the difference between up and downgazes was 15–≤ 25 PD and 8–10 mm if the difference >25 PD.

Horizontal muscle adjustments were based on Kenneth Wright’s tables for strabismus.[18] We decreased the amount of resection/plication by 1 mm according to the surgeon’s experience.

Statistical analysis

The collected data was analyzed using the Statistical Package for the Social Sciences (SPSS) version 28 (IBM Corp., Armonk, NY, USA). Data was double checked for normality using normality plots and the Shapiro–Wilk test. Data was summarized using mean and standard deviation in quantitative data and using frequency (count) and relative frequency (percentage) for categorical data. Comparisons between groups were done using an unpaired t-test in normally distributed quantitative variables, while a non-parametric Mann–Whitney test was used for non-normally distributed quantitative variables. Comparison between pre- and postoperative values was done using a paired t-test in normally distributed quantitative variables, while the non-parametric Friedman test and Wilcoxon signed rank test were used for non-normally distributed quantitative variables.[19] For comparing categorical data, Chi-square (χ2) test was performed. An exact test was used instead when the expected frequency was less than 5.[20] P-values less than 0.05 were considered significant.

Results

A total of 64 patients were reviewed, 32 were treated with bilateral medial rectus plication and vertical transposition (Group I), and 32 patients were treated with bilateral medial rectus resection and vertical transposition (group II). Each group was further divided into two subgroups: A and V. The mean age of all patients at the time of operation was 15.95 ± 12.79 years (range: 4–50). Table 1 shows the preoperative criteria in both groups (no significant difference between the two groups).

Table 1.

Preoperative data for the studied groups

Variables		Group I (No.=32)		Group II (No.=32)		P
Age in years: mean±SD (range)		16.1±12.7 (4–50)		15.8±13.1 (4–50)		0.82
Male sex: No. (percent)		15 (46.9)		17 (53.1)		0.62
A-pattern: No. (percent)		12 (37.5)		11 (34.4)		0.79
V-pattern: No. (percent)		20 (62.5)		21 (65.6)		0.79
Preoperative angle of XT in PD: mean±SD (range)		40.6±7.2 (30–55)		41.1±7.5 (30–55)		0.8
Preoperative pattern in PD: mean±SD (range)		21.3±3.7 (15–30)		21.6±4.4 (15–35)		0.73
Refraction: mean±SD (range)		0.24±3.09 (−5.5–6)		0.06±3.1 (−5.5–4.75)		0.82
BCVA: mean±SD (range)		0.78±0.16 (0.4–1)		0.80±0.17 (0.4–1)		0.58
Preoperative grading of stereopsis, No., percent		Poor (32, 100)		Poor (32, 100)		0.42

BCVA=best corrected visual acuity, No.=number, PD=prism diopters, SD=standard deviation, XT=exotropia

Table 2 shows the intraoperative data and the postoperative outcomes in both groups. Postoperative angles at 6 months were 4.6 ± 6.0 and 2.53 ± 6.5 PD exodeviation, respectively (no significant difference in both groups regarding postoperative horizontal deviation, P = 0.185). No significant difference was found between the two groups regarding stereopsis as a sensory outcome (P = 0.56) [Figs. 2-4].

Table 2.

Intraoperative and postoperative data in both groups

Variables		Group I (No.=32)		Group II (No.=32)		P
Amount of MR plication/resection, mm, mean±SD (range)		4.6±0.8 (3–6)		4.6±0.9 (3–6.5)		0.87
Amount of MR transposition, mm, mean±SD (range)		6.1±2.1 (5–10)		6.1±2.1 (5–10)		1
Postoperative XT at 1 m, PD, mean±SD (range)		−1.4±6.6 (−25 to 10)*		−1.8±6.5 (−25 to 10)		0.33
Postoperative XT at 6 m, PD, mean±SD (range)		4.6±6.0 (−12 to 20)		2.5±6.5 (−15 to 20)		0.19
Pattern collapse		16.7±5.6		16.1±4.1		0.65
Postoperative grading of stereopsis, No., percent		Poor (7, 21.9) Moderate (24, 75) Good (1, 3.1)		Poor (6, 18.8) Moderate (25, 78.1) Good (1, 3.1)		0.56

MR=medial rectus, No.=number, PD=prism diopters, SD=standard deviation, XT=exotropia, *Minus sign refers to esotropia and vice versa

Figure 2.

(a) Preoperative photograph of a 34-year-old female with Lt. constant exotropia (middle photo) and A-pattern (middle, bottom photo). (b) Preoperative measurements of the same patient. Neutralization of the red reflex by 45 base in prism (middle photo), measuring exotropia in upgaze by asking the patient to make her chin down (30 prism exotropia in upgaze) (top photo), measuring exotropia in downgaze by asking the patient to make her chin up (50 prism exotropia in downgaze) (bottom photo)

Figure 4.

(a) Preoperative photograph of a 10-year-old child with Rt. constant exotropia (middle photo) and V-pattern (middle, top photo). (b) Early postoperative follow-up of the same child showing orthophoria (middle photo) and collapse of pattern (top and bottom photos)

Figure 3.

(a) Postoperative follow-up at 1 month of the same patient in Figure 2 shows orthophoria (middle photo) and collapse of A-pattern deviation (top and bottom photos). (b) Postoperative follow-up at 6 months of the same patient in Figure 2, showing orthophoria (middle photo) and collapse of pattern deviation (top and bottom photos)

Regarding pattern deviation, the mean preoperative pattern deviation (difference in prism diopters between up and down gazes) was 21.3 ± 3.7 PD in group I, with a postoperative pattern collapse of 16.7 ± 5.6 PD. In group II, the mean preoperative pattern deviation was 21.6 ± 4.4 PD, with a postoperative pattern collapse of 16.1 ± 4.1 PD. Change between pre- and postoperative pattern deviation was significant in each group. The percentage of success in pattern collapse (pattern deviation ≤8 PD) was 90.6% in group I and 84.4% in group II. There was no significant difference in success between the groups (P = 0.708). There were no intra- or postoperative complications recorded. The results of the subgroups regarding pattern deviation are shown in Table 3, which shows a significant collapse in pattern deviation postoperatively in the four subgroups.

Table 3.

Preoperative pattern and postoperative surgical correction in subgroups (Mean±SD)

		Group I				Group II
		A-pattern (No.=12)		V-pattern (No.=20)		A-pattern (No.=11)		V-pattern (No.=21)
Preoperative pattern, PD		21.3±3.8		21.3±3.7		20.5±4.2		22.2±4.4
Postoperative pattern, PD		5.4±5.3		4.1±3.2		5.4±5.6		5.5±3.9
P* (between pre- and postoperative values)		0.002*		<0.001*		0.003*		<0.001*
Surgical success in pattern, No., percent		10 (83.3)		19 (95.0)		9 (81.8)		18 (85.7)

No.=number; PD=prism diopters, *significant (Non-parametric Wilcoxon signed rank test)

Discussion

Pattern deviation can be corrected either by oblique muscle surgery in cases with significant oblique muscle overaction or with horizontal muscle transposition in cases without oblique overaction. In this retrospective study, we chose only cases with constant or intermittent exotropia with no oblique overaction. We compared the effect of bimedial plication and transposition as an alternative technique with bimedial resection and transposition as the standard. Muscle transposition was prescribed in literature either by doing complete muscle disinsertion, as in the Knapp procedure, or without muscle disinsertion, as in the Nishida procedure. However, both do not have a strengthening effect; they aim only to change the pulling force of the muscle.[12]

Gokyigit B et al. were the first to present this technique (rectus plication and transposition) and named it “sliding shape extraocular muscle transposition with plication procedure (SSMTP).”[12,21] There were 10 cases in their study (out of 17 cases) with exotropia and vertical deviation, five of them were treated by medial rectus plication and transposition as a primary surgical intervention, except one case, who had undergone surgery before. There was no anterior segment ischemia even in cases who had undergone three recti muscles surgery on the same eye. Of 10 cases of exotropia, five achieved pattern deviation of less than or equal to 8 PD, and three achieved horizontal deviation within 10 PD of orthophoria. They prescribed this technique to be safe, effective, and with good results on long-term follow-up (between 24 and 40 months). Our study differed from Gokyigit B et al. in that our sample size was larger (32 patients), and we chose only cases of unoperated exotropia. However, the follow-up period was shorter (6 months).

Additionally, Shah PR and Pihlblad MS published a report of four successful cases of complex horizontal and vertical squint, who were treated with unilateral recession/plication with vertical transposition.[14] The technique was effective, and all four cases achieved the required ocular alignment for both horizontal and vertical deviations. No ischemia occurred even in cases with previous squint surgery in the same eye.

In our study, both horizontal and vertical successes were achieved in both groups. Success in horizontal deviation was defined as being within 10 PD of orthophoria at 6 months postoperatively. The percentage of success in group I was 81.3% (26 out of 32 patients) and in group II was 84.4% (27 out of 32), with no significant difference between the groups, P = 0.74. ElKamshoushy A also reported good results with bimedial resection in cases of unoperated exotropia, success rate was 77%.[22] However, the study included only cases with large-angle exotropia.

According to the surgical design in group I, we used a limbal approach and a double-armed 6/0 Vicryl suture, which passed from the muscle center to the periphery on both sides and was tied. The two sutures were then tied after passing through partial scleral thickness. In Shah and Pihlblad’s study, the fornix approach was used, and two separate single-armed polyglactin sutures were passed at the muscle edges and tied.[14] Gokyigit B et al. used a limbal approach and either single- or double-armed sutures. In six patients, they added a central 6/0 Dacron suture to make the whole muscle edge at the same plication line to maintain the effect of plication.[12,21]

We believe that our technique avoids muscle splitting and decreases the need for a central muscle suture to enforce the effect of plication. One disadvantage we noticed was that sheath wiring of the sclera may occur after tying the sutures if the scleral paths are too superficial. This can be avoided by proper passage through the sclera and avoiding superficial paths.

Our results in plication and resection were comparable, with no significant difference between the groups. This is like many studies that recorded similar results between plication and resection.[23,24,25,26] Daga et al.[26] reported the results of a modified surgical technique of muscle to sclera plication with reinforced sutures to maintain the effects of plication and avoid long-term muscle relaxation and fading of plication effect. Results were comparable to resection in the treatment of exotropia.

Anterior segment ischemia is a rare complication of strabismus surgery that occurs secondary to muscle disinsertion, either by recession or resection. The risk increases if three muscles are operated on in the same eye. Plication provides a viable alternative to muscle resection, preserving anterior ciliary circulation especially in surgeries where three-muscle surgery is needed.[24]

Pattern collapse was unsuccessful in three cases (9.4%) in group I and five cases (15.6%) in group II (P = 0.708). The causes of residual pattern may be related to unrecognized oblique overaction, inaccurate measurements of pattern preoperatively, or improper execution of the surgical technique.

The age, demographic, and preoperative data were comparable with no significant differences in both two groups. Other strength points in our study were as follows: the presence of a control group and the average follow-up period of 6 months.

However, a larger sample is needed, and a longer follow-up period is recommended to address the long-term effects of the new technique.

Conclusion

We find that horizontal transposition of plicated medial rectus muscle is a safe, rapid, and effective technique for correcting cases of exotropia with A- or V-patterns without associated oblique muscle overaction.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Lamiaa El-aidy and Manar Ghaly. Literature research and the first draft of the manuscript were done by Lamiaa El-Aidy. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Ethical approval

The study was approved by the Zagazig University Institutional Review Board (IRB), ZU-IRB #8092/10-10-2021.

Compliance with ethics guidelines

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1964, as revised in 2013. Informed consent was obtained from all patients included in the study.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Conflicts of interest:

There are no conflicts of interest.

Funding Statement

Nil.