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Table of Contents
ORIGINAL ARTICLE
Year : 2023  |  Volume : 5  |  Issue : 1  |  Page : 22

Long-term surgical outcomes of unilateral horizontal muscle strabismus surgery in patients with sensory esotropia versus sensory exotropia


1 Department of Ophthalmology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
2 Department of Cardiology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India

Date of Submission10-Nov-2022
Date of Decision29-Dec-2022
Date of Acceptance09-Jan-2023
Date of Web Publication27-Jun-2023

Correspondence Address:
Anupam Singh
Department of Ophthalmology, All India Institute of Medical Sciences, Rishikesh - 249 203, Uttarakhand
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/pajo.pajo_62_22

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  Abstract 


Purpose: To compare the long-term postoperative outcomes of unilateral horizontal muscle strabismus surgery in patients with sensory esotropia and sensory exotropia.
Methods: This retrospective study included 30 patients of sensory deviation who underwent strabismus surgery between January 2017 and December 2020 and had 24 months of follow-up. The patients were classified into Group A (sensory esotropia) and Group B (sensory exotropia) of 15 each. The successful outcome was assigned to a patient with postoperative deviation ≤10 prism dioptres (PD) in primary position.
Results: The mean age of the sample was 20.87 ± 6.88 years, 18 were male (60%) and 12 were female (40%). The mean preoperative deviation in Group A was 38.8 ± 10.46 PD and in Group B, it was 48.0 ± 5.92 PD. Successful surgical outcome (≤10 PD) at postoperative day 1 was achieved in 29 patients (96.77%). One patient (3.33%) having sensory exotropia was found to have residual deviation >10 PD. These results were maintained at the 6th month and 12th month of follow-up and there was no significant difference between surgical outcomes of both groups (Chi-square test, P = 0.309). At the 24th month follow-up, 23 patients maintained good surgical outcome; all seven patients who had surgically failed outcome (>10 PD) belonged to the exotropia group, which was statistically significant (Chi-square test, P = 0.002). The mean postoperative deviation at the final visit at 24 months of follow-up in Group A was 3.6 ± 2.16 PD and in Group B, it was 10.87 ± 2.82 PD. The long-term outcomes are significantly worse in patients of sensory deviations with organic vision loss and sensory exotropia. Other factors which determined the long-term successful postoperative outcome were best-corrected visual acuity (BCVA), childhood-onset strabismus, and younger age at surgery.
Conclusions: Good primary position alignment can be achieved in patients with sensory deviations with single strabismus surgery. Type of deviation, BCVA, age of onset, and age at the time of surgery were the factors associated with successful long-term alignment.

Keywords: Long-term outcome, sensory deviation, sensory esotropia, sensory exotropia


How to cite this article:
Singh A, Sharma S, Singla A, Kumawat D, Agrawal A, Kumar B. Long-term surgical outcomes of unilateral horizontal muscle strabismus surgery in patients with sensory esotropia versus sensory exotropia. Pan Am J Ophthalmol 2023;5:22

How to cite this URL:
Singh A, Sharma S, Singla A, Kumawat D, Agrawal A, Kumar B. Long-term surgical outcomes of unilateral horizontal muscle strabismus surgery in patients with sensory esotropia versus sensory exotropia. Pan Am J Ophthalmol [serial online] 2023 [cited 2023 Sep 27];5:22. Available from: https://www.thepajo.org/text.asp?2023/5/1/22/379763




  Introduction Top


Poor vision due to amblyopia or any other organic cause commonly leads unilateral strabismus which is also known as sensory deviation. Sensory deviation occurs as a result of primary sensory deficit followed by partial or complete disruption of fusion.[1] The type of horizontal sensory strabismus depends upon the age at the onset of vision loss. Visual loss occurring in childhood commonly leads to esotropia, whereas that occurring in adulthood leads to exotropia, suggesting that late onset vision loss induces exotropia more frequently than does congenital or early onset vision loss.[2],[3]

The primary objective of strabismus surgery is to achieve primary position alignment to restore binocularity and stereopsis, to eliminate abnormal head posture and symptoms such as diplopia and asthenopia. However, in cases of sensory deviation, it may not be possible to achieve all of these objectives. Hence, surgical treatment in these patients is mainly directed toward improving the cosmetic appearance by achieving primary position alignment.[1] Most patients with such type of deviation want to avoid surgery on the sound eye, as they are dependent on it. Therefore, the option of surgery is usually confined to the eye with the visual deficit or the nonseeing eye.[2]

Amblyopia has been believed to be a poor prognostic factor for achieving primary position alignment in both children and adults.[4],[5],][6] Poor vision due to organic lesion can further spoil the broth. There are very few published studies on the surgical outcomes of unilateral horizontal muscle strabismus surgery in sensory deviations and even fewer have studied the factors affecting long-term outcomes in these patients.[7],[8],[9],[10]

The purpose of this retrospective study is to compare the long-term postoperative outcomes of sensory esotropia with those of sensory exotropia and explore the determinants of long-term outcomes of unilateral horizontal muscle strabismus surgery these patients.


  Methods Top


This retrospective study was approved by the Institutional Ethics Committee (AIIMS/IEC/21/433 dated July 16, 2021) and followed the tenets of Declaration of Helsinki. The clinical records of all patients with horizontal unilateral strabismus with poor vision (exotropia/esotropia) who underwent strabismus surgery between January 2017 and December 2020 were reviewed retrospectively. Patients with monocular vision loss (best-corrected distance visual acuity 6/60 or worse) due to organic pathologies and amblyopia were included in the study. Patients with bilateral vision loss, paralytic or restrictive strabismus, vertical strabismus, oblique muscle overaction, postoperative follow-up <24 months, and history of previous strabismus surgery were excluded. Patient details such as gender, age of onset of vision loss, possible etiology of vision loss, age of onset of deviation, and age at the time of surgery were noted.

Preoperative ophthalmic examination details including assessment of visual acuity (with Snellen chart), best-corrected visual acuity (BCVA), cycloplegic refraction, type of deviation, preoperative deviation in prism diopters (PD) by Krimsky test for both near and distance, abnormal head posture, diplopia, and ocular motility using standard −4–+4 grading scale were retrieved from the records of the patients. Details of medical history, slit-lamp examination, and dilated fundus examination were also recorded for every patient.

As per the records, informed consent was obtained before surgery, which comprised of information regarding alternative procedures, possible outcomes, limitation of horizontal gaze, lid aperture changes, and need for re-surgery. All surgeries were performed under local or general anesthesia by a single surgeon. Surgical correction was planned according to modified Park's table after considering the type and amount of horizontal deviation and forced duction test for each patient. All patients were operated by limbal-conjunctival approach. Recession and resection were performed only in the eye with poor vision.[7] All the patients were followed up at postoperative day 1, 2 weeks, 1 month, 6 months, 12 months, and 24 months.

The patients were further classified into two groups according to the type of horizontal deviation as follows: Group A, sensory esotropia and Group B, sensory exotropia. The age of onset of vision loss and deviation were classified as childhood onset if it occurred before 8 years of age and adult onset if it occurred after 8 years of age. The successful outcome was assigned to a patient with postoperative deviation ≤10 PD in primary position at any postoperative visit. Clinically, significant postoperative drift was defined as a difference of ≥5 PD in consecutive postoperative primary position deviations at 12 and 24 months.

Statistical analysis

Descriptive statistics for the quantitative variables were summarized as mean ± standard deviation using the Kolmogorov–Smirnov test of normality. For categorical variables, Chi-square test/Fisher's exact test was utilized. A two-tailed P < 0.05 was considered statistically significant. Data were tabulated in Microsoft Excel Spread sheet (Microsoft Corporation, USA) and analyzed using the Statistical Package for the Social Sciences (SPSS) software version 28.0 (IBM Corp., Armonk, NY, USA). The correlation matrix and plot were described using the jamovi project (2021) jamovi (Version 2.2).


  Results Top


A total of 48 patients with sensory deviation underwent strabismus surgery during the time frame of this retrospective study. Out of these 48 patients, 10 were excluded due to incomplete records and eight had follow-up <24 months. Thus, 30 patients who fulfilled the inclusion criteria were recruited to this study. The mean age of the sample was 20.87 ± 6.88 years, 18 were male (60%) and 12 were female (40%). In 13 (43.33%) patients, the right eye was affected and in 17 (56.67%), the left eye was affected.

The BCVA of the worse eye varied between 6/60 and 1/60. The mean preoperative deviation of patients with BCVA of 6/60 (n = 8) was 44.37 ± 8.21 PD, those between 2/60 and 5/60 (n = 9) was 39.11 ± 9.98 PD, and those with 1/60 (n = 13) was 45.76 ± 9.75 PD. There was no statistically significant difference among the subgroups (P = 0.321).

Depending upon the type of deviation, the study population was divided into two groups, Group A with sensory esotropia and Group B with sensory exotropia. Both groups had 15 participants each. The baseline characteristics of both groups are summarized in [Table 1].
Table 1: Baseline, preoperative findings, and postoperative outcomes of Group A and B

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Esotropia was present in 15 (50%) cases and exotropia was present in the remaining 15 cases (50%). The mean age of patients with esotropia was 18.83 ± 6.75 years and mean age of patients with exotropia was 23 ± 6.39 years. Patients with anisometropic or strabismic amblyopia were 18 (13 in Group A and 5 in Group B), whereas 12 patients (2 in Group A and 10 in Group B) had organic lesion.

Vision loss occurred during childhood in 28 patients (93.33%), out of which 15 (53.57%) patients developed esotropia and 13 (46.43%) had exotropia. Two patients (6.67%) had adult-onset vision loss and both of them developed exotropia. Onset of strabismus was during childhood in 25 patients (83.33%) and in adulthood in five patients (16.67%).

The mean preoperative deviation in Group A was 38.8 ± 10.46 PD and in Group B, it was 48.0 ± 5.92 PD, the difference was statistically significant (P = 0.007).

The mean postoperative deviation at the 6th month follow-up was 6.4 ± 1.55 PD and 5.07 ± 2.25 PD in Group A and Group B, respectively (P = 0.071); at 12th-month follow-up it was 5.8 ± 1.61 PD and 6.53 ± 2.8 PD in Group A and Group B, respectively (P = 0.389). The mean postoperative deviation at the 24th-month follow-up in Group A was 3.6 ± 2.16 PD and in Group B, it was10.87 ± 2.82 PD (P < 0.001). Thus, there was insignificant difference between postoperative alignments of the two groups at 6 and 12 months of follow-up, but there was a statistically significant difference at 24 months of follow-up.

Successful surgical outcome (≤10 PD) at the postoperative day 1 was achieved in 29 patients (96.77%). One patient (3.33%) having sensory exotropia was found to have residual deviation >10 PD. These results were maintained at the 6th month and 12th month of follow-up and there was no significant difference between the surgical outcomes of both groups (Chi-square test, P = 0.309). At the 24th month follow-up, 23 patients maintained good surgical outcome; all seven patients who had surgically failed outcome (>10 PD) belonged to the exotropia group, which was statistically significant (Chi-square test, P = 0.002). [Table 2] summarizes the factors associated with postoperative outcomes.
Table 2: Factors associated with long-term postoperative outcomes

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Patients with preoperative deviation <50 PD had more successful postoperative outcome than those with preoperative deviation >50 PD. The difference was statistically significant at the 6th and 12th month follow-up (Chi-square test, P = 0.009) but became insignificant at 24th month follow-up (Chi-square test, P = 0.175).

All amblyopic patients (n = 18) maintained successful surgical outcome throughout the follow-up period of 24th months. However, the patients who had organic lesion (n = 12), 11 were successfully aligned till 12 months, out of which 7 failed to maintain postoperative deviation ≤10 PD at 24 months. Drift in primary position deviation was significantly greater in patients belonging to organic lesion group as compared to amblyopia group at the 6th and 12th month follow-up (Chi-square test, P < 0.0001) as well as 24th-month follow-up (Chi-square test, P = 0.0002).

BCVA (in worse eye) >1/60 was associated with more successful postoperative maintenance of primary position alignment at 24 months of follow-up as compared to patients operated with BCVA (in worse eye) <1/60. The difference was statistically insignificant at 6 months and 12 months follow-up (Chi-square test, P = 0.508) and significant at 24-month follow-up (Chi-square test, P = 0.0009) [Table 2].

Childhood onset strabismus was found to have more successful postoperative outcome as compared to adult-onset strabismus with statistically significant difference at the 6th-month (Chi-square test, P = 0.023), 12th-month (Chi-square test, P = 0.023) as well as 24th month (Chi-square test, P = 0.014) follow-up.

Association of age at surgery with primary position alignment was statistically significant at 24th-month follow-up (Chi-square test, P = 0.018) where it was found that out of 30 patients, 7 who had surgically failed outcome were above the age of 20 years. This difference was statistically insignificant at the 6th- and 12th-month follow-ups (Chi-square test, P = 0.636).

Pearson correlation coefficient was used for correlation preoperative (PD) and postoperative deviation (PD) at 6 months, 12 months, and 24 months in Groups A and B. For Group A, a significant positive correlation was seen between 6 months and 12 months postoperative period with correlation coefficient 0.835 while nonsignificant positive correlation was noticed between preoperative and postoperative deviation at 6 months, 12 months, and 24 months with correlation coefficient of 0.472, 0.307, and 0.122, respectively. Similarly, nonsignificant positive correlation was seen between 6 months and 24 months postoperative period and 12 months and 24 months postoperative period with correlation coefficient values 0.136 and 0.262, respectively [Figure 1].
Figure 1: Pearson correlation plot showing a significant positive correlation between 6 months and 12 months, while nonsignificant positive correlation between preoperative and postoperative deviation at 6 months, 12 months, and 24 months in Group A

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For Group B, the correlation between preoperative deviation and postoperative deviation at 6 months and 12 months period was found to be positive but nonsignificant while a significant positive correlation was found at 24 months period with correlation coefficient of 0.225, 0.285, and 0.512, respectively. In addition, highly significant positive results were obtained between 6 months and 12 months, 6 months and 24 months, and 12 months and 24 months postoperative period with correlation coefficient of 0.901, 0.788, and 0.795, respectively [Figure 2].
Figure 2: Pearson correlation plot showing a positive but nonsignificant correlation between preoperative deviation and postoperative deviation at 6 months and 12 months while a significantly positive correlation at 24 months in Group B

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  Discussion Top


The surgical outcomes of strabismus are determined by various clinical factors including visual acuity, angle of preoperative deviation, axial length, refractive error, age of onset of vision loss, etiology of vision loss, age of onset of strabismus, age at the time of surgery, surgical technique, surgical amount, stereopsis, and fusion.[8],[9] Management of unilateral strabismus with poor vision mainly aims at primary position alignment for cosmesis. Rather than a simple esthetic procedure, it should be considered a reconstructive procedure due to the functional improvement observed after these surgeries. It also addresses the negative psychosocial impact of the condition on the patient.

In cases of unilateral strabismus with poor vision, generally surgery only on the visually compromised eye is preferred because it may be difficult to persuade the patient to undergo a surgery on the seeing eye. The long-term maintenance of postsurgical alignment is expected to be poor and the recurrence rate is high due to the low chance of regaining stable fusion in these cases.[7],[9],[10]

Some authors have reported the use of botulinum toxin injection as a good alternative to surgery as it is noninvasive, but it's use is limited as repeated injections are required for correction of misalignment. Dawson et al. have obtained good results in 8% of the cases, 20% needed repeated injections, and 43% eventually needed surgery for correction.[4] In the largest series of sensory strabismus patients to date, Maruo et al. reported that 165 (14.9%) out of 1105 patients with sensory strabismus had undergone strabismus surgery and all 165 patients achieved successful results with a total of 173 surgeries.[11] Makino et al. have achieved a final postoperative deviation of <10 PD in 6 out of seven patients.[12] Oral et al.[13] reported an overall 75.9% surgical success rate, with 87.5% for the exotropia group and 61.5% for the esotropia group. Martinez et al. reported a 41.2% surgical success rate for amblyopic patients with esotropia.[6] Similarly, Merino et al. reported a high surgical success rate in sensory strabismus in patients who underwent unilateral, bilateral or multiple procedures.[14] The difference between success rates reported in these studies may be a result of different follow-up periods at which the correction was reported, and also the different criteria for surgical success considered in these studies.[15]

In current study, patients with childhood-onset vision loss were more prone to develop esotropia where as those with adult-onset vision loss had tendency to develop exotropia. Further analysis indicated that this difference cannot be not explained by age of onset of vision loss alone, as there was no significant difference between the age of onset of vision loss and the direction of deviation (P = 0.48). Thus, this can be concluded that patients having organic cause of vision loss had more tendency to develop exotropia irrespective of age of onset of vision loss. Patients with childhood onset strabismus were more prone to develop esotropia whereas those with adult-onset strabismus were prone to develop exotropia, which was statistically significant (P = 0.042).

The association between BCVA at presentation and postoperative deviation at 24 months was statistically significant (P = 0.0009). This is consistent with the findings of Erkan Turan et al.[8] who observed that success rates in the long term were well-predicted by visual acuity.

There was a statistically significant association between age at onset of strabismus and postoperative deviation, with childhood-onset strabismus having more successful outcome than adult-onset strabismus at 6 months, 12 months (P = 0.023) and 24 months (P = 0.014) of follow up. Further, association of age at surgery with primary position alignment was statistically significant at 24 months of follow up (P = 0.018), which shows that the chances of a failed outcome increases if the surgery is delayed and age increases. This can be explained by the fact that younger patients may have a better chance of sensory fusion after strabismus surgery and as age increases muscle contracture and other soft tissue changes also come into play which can have adverse effects on the final outcome. However, this cannot be concluded by the present study due to the small sample size and requires further study.[8] Preoperative deviation of <50 PD was significantly associated with more successful postoperative outcome than those with a deviation of >50 PD in the early postoperative period up to 12 months of follow up (P = 0.009), following which the results became insignificant at 24 months of follow up (P = 0.175).

In the present study, in Group A, most patients had amblyopia (86.67%), which included anisometropic as well as strabismic amblyopia, whereas Group B patients mostly had organic lesions (66.67%). Group B patients with exotropia had significantly worse BCVA (1/60) at presentation (P = 0.009). Furthermore, there was a statistically significant difference between preoperative deviations of the two groups (P = 0.007). However, the mean preoperative deviation was not significantly different between patients with varying magnitudes of vision loss across Groups A and B (P = 0.321).

There was no significant difference in postoperative deviation at 6 and at 12 months (P = 0.309) between the two groups. However, at 24 months of follow up, the difference was found to be significant (P = 0.002). All 15 patients of group A had successful outcome, whereas 7 out of 15 patients of Group B had unsuccessful outcome at 24 months follow up (P = 0.002).

For surgical outcomes in Group A and B, Pearson's correlation was utilised to compare preoperative and postoperative deviation (PD). In Group A, positive correlation was found in all the comparison groups but it was significant only between 6 months and 12 months postoperative period (P < 0.001) while in Group B significant positive outcome between preoperative and 24 months postoperative deviation (P = 0.048) and highly significant positive outcome between 6 months, 12 months and 24 months was found with P < 0.001 in all cases. Thus, there is increased tendency of postoperative deviation to be more than >10 PD (treatment failure) in Group B than Group A highlighting better surgical outcomes for patients with sensory esotropia as compared to patients with sensory exotropia.

This is in consistency with the findings of Portes et al., where there was a surgical success rate of approximately 50% in exotropic patients with at least 6 months of follow-up.[16] In contrast to our study, Yurdakul reported acceptable outcomes in 73.9% of esotropia cases and 80.6% of exotropia cases with one surgery after a follow-up period of at least 1 year.[17]

Oliveira et al. defined success as a residual deviation of up to 15 PD and reported a 90% surgical success rate.[18] With more stringent criteria for success such as ours (residual deviation of up to 10 PD), the proportion of cases with successful outcome comes to about 76.6%. This result corroborates with the study of Kim et al., which reported that 8 (72.7%) of their 11 patients showed alignment within 10 PD at 1 month postoperatively.[15] Erkan Turan et al. reported success rates to fall from 62.5% at short term of 2–3 months to 42.1% at long-term follow-up of approximately 2 years on an average.[8] In our study, 76.6% of patients had favorable outcome at the long-term follow-up of 24 months. This can be concluded that good and stable primary position alignment can be achieved in patients of sensory deviations even with single strabismus surgery in about half of all cases. However, it is very important to explain patients about follow-up for extended periods after surgery for sensory deviations, with counseling regarding the expectations of stabilization of correction only after 24 months of follow-up.

A postoperative drift of ≥5 PD was observed more commonly among patients of Group B between 6 and 24 months follow-up, which concurs with the findings of Erkan Turan et al. whose surgical success rate was lower in exotropic patients.[8] This disagrees in part with the findings of Oral et al.[13] who remarked that success might be more limited in sensory esotropia due to congenital causes in particular. In our cohort, drift in primary position deviation was significantly greater in patients belonging to sensory deviation due to organic causes as compared to amblyopic cause at 6 and 12 months (P < 0.0001) as well as 24 months follow-up (P = 0.0002). It may be concluded that the direction of deviation is important in determining the risk of having an unsuccessful long-term outcome along with the underlying etiology. Postoperative outward drift is expected in patients with poor vision due to organic lesions on long-term follow-up.

This study has some important limitations such as small sample size resulting in inadequate size for subgroup analysis, the retrospective design, and unequal distribution between the etiological groups. However, it presents a detailed picture of the predictors and considerations of surgical success in cases of sensory deviations, which are important in determining the cosmetic and functional acceptability of such procedures to patients.


  Conclusion Top


In summary, long-term outcomes are significantly worse in patients of sensory deviations with organic vision loss and sensory exotropia, with clinically significant drifts occurring between 6 and 24 months of follow-up. Other factors which determine a long-term successful postoperative outcome are BCVA at presentation, childhood-onset strabismus, and younger age at surgery.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Wright KW, Spiegel PH. Pediatric Ophthalmology and Strabismus. Vol. 2. New York: Springer; 2003. p. 221.  Back to cited text no. 3
    
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Martinez AA, Goldchmit M, Camargo GB, Souza-Dias C. Surgical correction of esotropia in eccentric fixation patients. Arq Bras Oftalmol 2005;68:645-8.  Back to cited text no. 6
    
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ssChang JH, Kim HD, Lee JB, Han SH. Supermaximal recession and resection in large-angle sensory exotropia. Korean J Ophthalmol 2011;25:139-41.  Back to cited text no. 7
    
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Erkan Turan K, Taylan Şekeroğlu H, Şener EC, Sanaç AŞ. Effect of visual acuity on the surgical outcomes of secondary sensory strabismus. Turk J Ophthalmol 2015;45:254-8.  Back to cited text no. 8
    
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Edelman PM, Brown MH. The stability of surgical results in patients with deep amblyopia. Am Orthopt J 1977;27:103-6.  Back to cited text no. 9
    
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Rosenbaum AL, Santiago AP. Clinical Strabismus Management. Philadelphia: W.B. Saunders Company; 1999. p. 193-9.  Back to cited text no. 10
    
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Maruo T, Kubota N, Maruo T. Surgical results of sensory strabismus at our clinic. Folia Jpn Ophthalmol Clin 2011;4:226-30.  Back to cited text no. 11
    
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Makino S, Hazawa K, Kondo R, Kanai M, Suto H, Ito K, et al. Surgical outcomes of sensory strabismus. Scholars J Appl Med Sci 2015;3:1791-3.  Back to cited text no. 12
    
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Oral AY, Ozgur O, Arsan AK, Oskan S. Surgical results in cases of sensory strabismus. Turk J Ophthalmol 2011;41:217-20.  Back to cited text no. 13
    
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Merino P, Mateos C, Gómez De Liaño P, Franco G, Nieva I, Barreto A. Horizontal sensory strabismus: Characteristics and treatment results. Arch Soc Esp Oftalmol 2011;86:358-62.  Back to cited text no. 14
    
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Kim MJ, Khwarg SI, Kim SJ, Chang BL. Results of re-operation on the deviated eye in patients with sensory heterotropia. Korean J Ophthalmol 2008;22:32-6.  Back to cited text no. 15
    
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Portes AV, Franco AM, Tavares MF, Souza-Dias CR, Goldchmit M. Surgical correction of permanent exotropia outcomes in amblyopic and non-amblyopic patients. Arq Bras Oftalmol 2011;74:267-70.  Back to cited text no. 16
    
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Yurdakul NS. Strabismus surgery in patients with low vision. Turk J Ophthalmol. 2013;43:313-6.  Back to cited text no. 17
    
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