Journal of Pediatric Ophthalmology and Strabismus

Original Article 

The Success of Unilateral Surgery for Constant and Intermittent Exotropia and Factors Affecting It in a Large Scandinavian Case Series

Rannveig Linda Thorisdottir, MD, PhD; Malin Malmsjö, MD, PhD; Kajsa Tenland, MD; Jonas Blohmé, MD, PhD; Helena Buch Hesgaard, MD, PhD

Abstract

Purpose:

To compare the results of surgery for constant and intermittent exotropia, to determine factors affecting surgical success, and to evaluate the effect of horizontal rectus muscle surgery on distance-near incomitance.

Methods:

In this retrospective study of 291 Scandinavian patients, inclusion criteria were surgery for constant (n = 101) or intermittent (n = 190) exotropia with no vertical deviation, no previous strabismus surgery, and available postoperative follow-up data. Medical records of patients (age: 3 to 85 years) undergoing surgery were reviewed. Surgical success was defined as postoperative esodeviation of less than 5 prism diopters (PD) to exodeviation of 10 PD or less.

Results:

Surgical success was 70% in constant exotropia and 80% in intermittent exotropia (P > .05). At follow-up 1.5 years after surgery, a significant drift was found in intermittent exotropia (P < .05). Different surgeons, spherical equivalents, anisometropia, amblyopia, gender, and age had no effect on surgical success (P > .05). The surgical success rate increased with decreasing preoperative angle (P < .05). Resection of the medial rectus muscle had a greater effect on the near deviation, whereas recession of the lateral rectus muscle had a greater effect on the distance deviation (P < .05).

Conclusions:

Surgical success was equally good in constant and intermittent exotropia, but better long-term stability was observed following surgery for constant exotropia. The only factor affecting surgical success was the preoperative deviation, with smaller deviations having a better outcome. A distance-near incomitance may be an important consideration in choosing the magnitude of medial versus lateral rectus muscle surgery.

[J Pediatr Ophthalmol Strabismus. 2021;58(1):34–41.]

Abstract

Purpose:

To compare the results of surgery for constant and intermittent exotropia, to determine factors affecting surgical success, and to evaluate the effect of horizontal rectus muscle surgery on distance-near incomitance.

Methods:

In this retrospective study of 291 Scandinavian patients, inclusion criteria were surgery for constant (n = 101) or intermittent (n = 190) exotropia with no vertical deviation, no previous strabismus surgery, and available postoperative follow-up data. Medical records of patients (age: 3 to 85 years) undergoing surgery were reviewed. Surgical success was defined as postoperative esodeviation of less than 5 prism diopters (PD) to exodeviation of 10 PD or less.

Results:

Surgical success was 70% in constant exotropia and 80% in intermittent exotropia (P > .05). At follow-up 1.5 years after surgery, a significant drift was found in intermittent exotropia (P < .05). Different surgeons, spherical equivalents, anisometropia, amblyopia, gender, and age had no effect on surgical success (P > .05). The surgical success rate increased with decreasing preoperative angle (P < .05). Resection of the medial rectus muscle had a greater effect on the near deviation, whereas recession of the lateral rectus muscle had a greater effect on the distance deviation (P < .05).

Conclusions:

Surgical success was equally good in constant and intermittent exotropia, but better long-term stability was observed following surgery for constant exotropia. The only factor affecting surgical success was the preoperative deviation, with smaller deviations having a better outcome. A distance-near incomitance may be an important consideration in choosing the magnitude of medial versus lateral rectus muscle surgery.

[J Pediatr Ophthalmol Strabismus. 2021;58(1):34–41.]

Introduction

Exotropia is a common condition compromising stereovision and psychosocial health in many children and adults.1 In Scandinavia, the cumulative incidence of exotropia among children has been reported to be 3.7 in 100,000 in a register-based study,2 whereas the prevalence of exotropia among adults has been reported to be 0.3% (95% CI: 0.2 to 0.6) in a large-scale population-based study.3 Exotropia is less common than esotropia in Western countries, whereas the opposite is observed in Asia.3–5

There is no general evidence-based consensus regarding the treatment of exotropia.6 Although the management of exotropia has been debated extensively in the literature, there is a lack of knowledge concerning which method of treatment is most effective, and the factors that influence the outcome. The use of nonsurgical treatment options to provide temporary symptom relief in small-angle intermittent exotropia has been advocated,7,8 but surgical intervention is recommended for constant and frequent intermittent exotropia. Surgical success rates for exotropia vary considerably between studies, from 38% to 91.6%, depending on the criteria used to define success and the follow-up period.9–11 A few small comparative studies have been carried out on the success of surgery for constant and intermittent exotropia. Some studies have reported that constant exotropia is a reliable predictor of poor surgical outcome.12 In another study with at least 1 year of follow-up, no difference was found in the results of surgical motor alignment between constant and intermittent exotropia, although patients with intermittent exotropia had a better surgical sensory outcome.13

Various risk factors have been reported to be significant for poor outcome, including younger age at operation for intermittent exotropia,14 worse sensory outcome with surgery in older patients, and longer duration of strabismus in cases of primary exotropia. Several studies have examined additional factors that might influence the surgical outcome, including stereoacuity, fusion reserves and extent of the deviation, refraction anomaly, amblyopia, and gender, with contradictory results.

The preoperative magnitude of the deviation and distance-near incomitance are thought to influence the surgical outcome. Some surgeons choose to do greater adjustment on the medial rectus muscle if the deviation is greater at near and the lateral rectus muscle if the deviation is greater at distance,15 although Archer16 questioned this rationale.

Overall, the results reported to date are ambiguous, and most studies have been done on Asian patients. Thus, there is a need for further studies of surgical outcome and factors affecting it, to optimize the results of treatment for constant and intermittent exotropia. To the best of our knowledge, this is the first large Scandinavian study undertaken to evaluate the surgical results for both constant and intermittent exotropia, and to elucidate the factors that might influence the surgical results.

Patients and Methods

This retrospective study is based on a review of the records of all patients who underwent surgery for constant or intermittent exotropia (ICD10: H501 and H503B) at the Department of Ophthalmology, Skåne University Hospital, Lund, Sweden, from 2011 to 2015. The inclusion criteria were no vertical deviation, no previous strabismus surgery, and 4 to 6 weeks of postoperative follow-up with orthoptic assessment. Data recorded included: name of the surgeon, age of the patient at the time of surgery (children younger than 18 years), gender, amblyopia, refraction measures of each eye, type of exotropia, and preoperative and postoperative (4 to 6 weeks postoperatively) deviation in primary position for near and distance gaze. The journals were thoroughly reviewed, and notes were made of reoperations and visits done later than 4 to 6 weeks after the operation. The spherical equivalent was calculated as the spherical correction plus half of the cylindrical correction. At the postoperative visit, the patients were asked how satisfied they were with the results of the operation (1 = not satisfied, 2 = moderately satisfied, or 3 = very satisfied).

All patients had undergone ophthalmological and orthoptic examinations prior to surgery. The orthoptic evaluation included prism and alternate cover test measurements at near (33 cm) and distance (6 m) gaze with best correction. A diagnostic occlusion test or a prism adaptation test was performed when necessary to discriminate between true divergence excess and pseudo-divergence excess exotropia. The strabismus surgery procedures were mostly unilateral (99.7%, 290 of 291), including unilateral combined medial rectus muscle resection and ipsilateral lateral rectus muscle recession (n = 281), unilateral medial rectus resection (n = 5), unilateral lateral rectus recession (n = 4), and only one case of bilateral medial rectus resection. Single-muscle surgery (lateral rectus recession or medial rectus resection) was performed if the angle of deviation was less than 20 PD, or if the surgeon evaluated the patient peroperatively and decided that adequate results would be obtained with surgery on one muscle. Limbal incisions were performed in all cases. The muscles were recessed or resected and reattached to the sclera with 6-0 polyglactin 910 sutures. Surgery was performed under either general (n = 218, 75%) or topical (n = 73, 25%) anesthesia.

The surgical strategy was based on evaluation of the preoperative deviation and the presence of incomitance. Furthermore, the non-dominant eye and the most deviating eye were selected. Surgery was performed by four experienced (> 10 years of experience) strabismus surgeons using individual surgical approaches. One surgeon (surgeon 2, Table 1) applied Parks' table,17 whereas the other three used Stigmar's approach (unpublished local Swedish surgical table). Stigmar's approach involves standardized recession of the lateral rectus muscle of 6.5 mm (< 14 years) and 7.5 mm (> 14 years), and resection of the medial rectus muscle of 1 mm per 5 PD; adjustment is made if there is distance-near incomitance. Objective surgical success was defined as 5 PD or less of esodeviation to 10 PD or less of exodeviation.18

Patient Characteristics (N = 291)

Table 1:

Patient Characteristics (N = 291)

Ethics

The Regional Ethics Committee at Lund University deemed that no ethical approval was required for this study. The design of the study and data collection conformed to national legislation and were compliant with the principles of the Declaration of Helsinki.19

Statistical Analysis

Statistical analysis was performed using SPSS software (IBM SPSS Statistics for Windows, version 23; IBM Corporation). The patients were divided into two groups: surgery for constant or intermittent exotropia. The Mann–Whitney test was used to compare the groups in terms of gender, age at operation, preoperative deviation, and total muscle movement (backward displacement of the lateral and medial rectus muscle shortening). Linear regression was used to compare postoperative deviation, and a binary logistic model was used to compare surgical success between the groups, having age and preoperative deviation as factors. A binary logistic regression model was used to identify factors affecting surgical success, where surgical success was the dependent factor, and surgeon, age of patient at operation (children younger than 18 years), gender, spherical equivalent, anisometropia, and amblyopia were used as factors. The reoperation rate in the two groups was compared using the Pearson's chi-squared test and it was also used to calculate differences in surgical success between the three groups defined by the preoperative distance deviation: small deviation (< 20 PD), moderate deviation, (20 to 40 PD), and large deviation (> 40 PD).

Statistical comparisons were performed between the deviation in primary position, before and after surgery, using the Wilcoxon signed-rank test, and to calculate significant differences in the deviation in patients with a follow-up of longer than 1 year. Simple linear regression was used to analyze the factors of muscle movement of the medial rectus and lateral rectus in the total change of the deviation in primary position for near and distance gaze. Significance was defined as a P value of less than .05.

Results

Patient Characteristics

A total of 633 patients underwent strabismus surgery during the inclusion period (2011 to 2015). More than half of these patients (n = 342) were excluded for the reasons shown in Figure 1. The total number of patients included in this study was thus 291. The patients' characteristics are given in Table 1. The main indication for surgery was asthenopia (n = 131). Other indications were psychosocial indications (n = 82), diplopia (n = 41), loss of stereopsis (n = 6), increasing angle of strabismus (n = 5), abnormal head posture (n = 2), and not recorded (n = 24).

Flow chart showing the patients excluded from the study.

Figure 1.

Flow chart showing the patients excluded from the study.

Surgical Success and Satisfaction Score in Constant and Intermittent Exotropia

A total of 223 patients exhibited objective surgical success at the 6-week follow-up visit (76.6%). The surgical success rate was 70% (71 of 101) in the constant exotropia group and 80% (152 of 190) in the intermittent exotropia group (P = .923, 95% CI = 0.537 to 1.989) (Table 2). Despite significant differences in age and preoperative deviation (P < .001), no significant difference was found in the postoperative deviation between the constant and intermittent exotropia groups (P = .363, 95% CI = −1.0 to 2.7) (Table 2). Patients undergoing surgery for intermittent exotropia had a significantly smaller preoperative deviation, and accordingly the total muscle movement was significantly less, than in patients undergoing surgery for constant exotropia.

Comparison of the Characteristics of Patients With Constant vs Intermittent Exotropia

Table 2:

Comparison of the Characteristics of Patients With Constant vs Intermittent Exotropia

Self-reported subjective satisfaction scores at the 6-week postoperative examination were available for 286 patients. Most of the patients (n = 272, 93.5%) were satisfied with the results. Only 14 (4.8%) patients described unsatisfactory results: 6 (2%) complained of too little effect (one of which had diplopia), 6 (2%) complained of overcorrection (one of which had diplopia), and 2 (0.7%) patients had diplopia, one despite the fact that the deviation was small in both near and far distance gaze and the other because of vertical deviation.

Surgical Outcome at the Postoperative Long-term Follow-up

Only 51 patients (17.5%) had long-term follow-up examinations including orthoptic measurements 1 year after surgery or later (15 patients with constant exotropia and 36 patients with intermittent exotropia) (Figure 2). In the constant exotropia group (n = 15), the median near and distance deviation did not change significantly from the 6-week examination to the long-term follow-up examination (P > .05). At the long-term follow-up examination, the distance deviation in the intermittent exotropia group had drifted significantly, from 10 PD at 6 weeks postoperatively to 16 PD (P < .001). The near deviation had also increased significantly, from 7 PD of exotropia at 6 weeks postoperatively to 16 PD (P = .002).

Change in the distance deviation in patients with constant exotropia and intermittent exotropia, preoperatively (white) and at follow-up after 6 weeks (dotted) and 1.5 to 2 years (hatched). The values shown are the median and range. PD = prism diopters

Figure 2.

Change in the distance deviation in patients with constant exotropia and intermittent exotropia, preoperatively (white) and at follow-up after 6 weeks (dotted) and 1.5 to 2 years (hatched). The values shown are the median and range. PD = prism diopters

Reoperation Rate

The reoperation rate was 4.4% (13 of 291) in the whole cohort or 19.6% (10 of 51) in the long-term cohort. This included 10 patients with exotropia (5 of whom had exotropic drift) and 3 who had immediate postoperative esotropia. There was no difference in the reoperation rate between the constant exotropia (2.4%, 7 of 291) and intermittent exotropia (2.1%, 6 of 291) groups (P = .141), and the average time to reoperation was 2 years.

Factors Affecting Surgical Success

The group with the smallest preoperative distance deviation (< 20 PD) had the highest success rate (95%; 40 of 42), followed by 78% (155 of 197) in the 20 to 40 PD group and 54% (28 of 52) in the greater than 40 PD group (P < .001). A significant reduction in the deviation between preoperative and postoperative values (P < .05) was found in all three groups.

No difference was seen in the surgical success rate between adults and children (P = .398, OR = 0.791 [95% CI = 0.459 to 1.363]), although the deviation at near was 10 PD higher for adults (35 PD, range = 12 to 75 PD) than for children (25 PD, range = 10 to 60 PD). Different surgeons, gender, spherical equivalent, amblyopia, and anisometropia had no significant influence on the surgical outcome (P > .05).

Effect of Medial Versus Lateral Rectus Muscle Surgery on Near and Distance Deviation

Our results show that resection of the medial rectus muscle had a greater effect on near deviation (3.21 PD/mm, P < .001, 95% CI = 2.33 to 4.10) than recession of the lateral rectus muscle (1.81 PD/mm, P < .001, 95% CI = 0.85 to 2.76) (R = 0.550). In contrast, recession of the lateral rectus muscle had a greater effect on distance deviation (2.88 PD/mm, P < .001, 95% CI = 2.13 to 3.63) than resection of the medial rectus muscle (2.41 PD/mm, P < .001, 95% CI = 1.72 to 3.10) (R = 0.653).

Discussion

Surgical Success and Satisfaction Score in Constant and Intermittent Exotropia

The findings of this study showed that surgical results were equally good in the groups with constant and intermittent exotropia. However, a significant exotropic drift was found in a small group of patients with intermittent exotropia at long-term follow-up. This is in agreement with the results of a long-term study by Holmes et al.6 One study concluded that successful postoperative motor alignment was the same in groups with constant and intermittent exotropia, and that sensory outcome was better in intermittent exotropia,13 and another found that younger age at surgery led to a better sensory outcome.20 Unfortunately, we were not able to include sensory outcome due to the retrospective design of this study, because information on stereovision was not complete. It has been suggested that deliberate initial overcorrection may be necessary to achieve a better long-term outcome.21,22 However, in a previous study on children with follow-up periods ranging from 6 months to 3 years, most patients exhibited exotropic drift, and this was greater among patients with initial postoperative consecutive esotropia (86.7%) than in patients with postoperative exotropia (26.1%).23 Several studies have revealed exotropic drift at long-term follow-up in patients with constant and intermittent exotropia,21,24–26 and some have reported more exotropic drift with younger age at surgery27 and greater preoperative angle of deviation.28 Thus, overcorrection may not necessarily lead to a better outcome.29

Surgical Success and Associated Factors

In the current study, surgical success was only significantly affected by the preoperative deviation as reported in previous studies.14,30–32 This is an important finding because it implies that greater recession/resection may be needed in the case of greater deviations, but a prospective randomized study is needed to confirm this hypothesis.

This study revealed no difference in surgical success between the groups with constant and intermittent exotropia, or between age groups. This agrees with the findings of Wu et al,13 Faridi et al,30 and Bukhari et al,33 who also included patients of all ages. However, it contrasts with the results of previous studies by Abroms et al20 and Choi et al.14 Gender, spherical equivalent, amblyopia, and anisometropia did not significantly influence the surgical outcome (P > .05), in accordance with the findings of some previous studies.22,32 However, anisometropia, lateral incomitance, and immediate postoperative undercorrection have previously been reported to increase the risk of poor outcome of surgery in intermittent exotropia.24 Furthermore, a shift in refractive error toward myopia has been reported to predict a favorable outcome in patients with primary exotropia31 and intermittent exotropia.34

Reasons for the differences in findings between studies could be differences in the population (Asians having more myopic eyes), the availability of sensory outcome data, and the method (duration of follow-up). The reason why we found no differences in surgical success between the surgeons (P > .05) could be explained by all of them being experienced surgeons (> 10 years' experience) and the use of individual surgical tables for unilateral surgical strategy. We were unable to find any other studies in which the results had been compared between different surgeons. Many studies have compared the results of unilateral lateral and medial rectus resection and bilateral lateral rectus recession strabismus surgery, but the results do not indicate whether one can be recommended over the other.10,14,30,35–41 It is therefore unlikely that this is a factor affecting surgical success. Unilateral surgery is the main procedure done at Skåne University Hospital because we find it appropriate to have one eye left unoperated if a second procedure is needed, to lessen the postoperative irritation to only one eye, because bilateral lateral recession does not seem to have better outcome, and due to the preference of the patients.

Reoperation Rate

The total reoperation rate was 4.4% (13 of 291) with an average time to reoperation of 2 years or 19.6% (10 of 51) in the long-term cohort. Oh and Hwang22 reported an estimated median time to failure after exotropia surgery of 48.3 months, with 35.3% showing recurrence and 4.4% overcorrection. In our study, only 14 (4.8%) patients were dissatisfied with the results. Of the undercorrected patients in our study, 93 (32%) patients had a deviation of greater than 10 PD at near and 84 (29%) patients had a distance deviation of greater than 10 PD, similar to the findings in a study by Faridi et al,30 but only a few of these patients (8 of 177) complained of undercorrection postoperatively, and 5 patients were overcorrected. The low reoperation rate, in comparison to the high number of under-corrected patients, may indicate the importance of evaluating the patient's needs (self-reported patient satisfaction), rather than measuring the deviation when deciding on further treatment. Self-reported questionnaire-based data are likely to be influenced by bias if not anonymized. However, these data may also reflect a true degree of symptom relief following surgery, despite some degree of undercorrection.

Effect of Medial Versus Lateral Rectus Muscle Surgery on the Deviation of Near and Far Distance Gaze

Previous studies by Burian et al15,42 were based on distance-near incomitance, and recommendations regarding different surgical procedures were based on unproven hypotheses that bilateral lateral rectus recession would affect the distance deviation more than the near deviation, and that a unilateral recession/resection procedure would affect the near and distance deviation equally. However, no such effect has been found in other studies.16,35 Our results suggest that movement of medial rectus muscle had a better effect on the near deviation and should cause the surgeon to make adjustments and choose to operate more on the medial rectus muscle rather than the lateral rectus muscle. Conversely, a larger deviation at distance would require more surgery on the lateral rectus muscle rather than the medial rectus muscle to ensure sufficient correction, which is in accordance with the unproven hypothesis of Burian et al.15,42

Strengths and Limitations

Our study has several strengths, which support our results. The large patient study group provides a homogeneous sample of cases of constant and intermittent exotropia including all ages (ie, children and adults), none of whom had undergone surgery previously for strabismus and none of whom had vertical strabismus. This enabled us to confirm the findings of previous studies in a Scandinavian population for the first time.

Nevertheless, this study has several limitations. The fact that the study is based on a retrospective case series is a source of bias and confounding. This could have affected the results, explaining the lack of significant findings regarding factors that might influence surgical results, and thus the disagreement with the results of some previous studies. Furthermore, the retrospective design resulted in limited information on postoperative incomitance, which could be anticipated because surgery was unilateral in almost the whole study population.43 Another limitation is the fact that four different surgeons were involved, with slightly different surgical strategies, which may have introduced bias affecting the identification of factors related to surgical success. The long-term follow-up was incomplete due to loss to follow-up, which may have led to the underestimation of the recurrence and reoperation rates. The short-term follow-up time was only 6 weeks, involving orthoptic measures without uniform stereovision measurements, preventing the evaluation of sensory outcome of the total study population.

Conclusions

In this unique Scandinavian study, we found that surgical success was equally good in patients with constant and intermittent exotropia, although a long-term drift in intermittent exotropia was noted. The only factor found to affect surgical success was the preoperative deviation, with less deviation predicting better outcome. This is important when planning strabismus surgery for patients with a large deviation, where movement in addition to that indicated in surgical tables might be needed to improve surgical success. A distance-near incomitance is also an important consideration when choosing the magnitude of muscle movement of the medial and lateral rectus muscles.

References

  1. Burke JP, Leach CM, Davis H. Psychosocial implications of strabismus surgery in adults. J Pediatr Ophthalmol Strabismus. 1997;34(3):159–164.
  2. Torp-Pedersen T, Boyd HA, Skotte L, et al. Strabismus incidence in a Danish population-based cohort of children. JAMA Ophthalmol. 2017;135(10):1047–1053. doi:10.1001/jamaophthalmol.2017.3158 [CrossRef]
  3. Hultman O, Beth Høeg T, Munch IC, et al. The Danish Rural Eye Study: prevalence of strabismus among 3785 Danish adults: a population-based cross-sectional study. Acta Ophthalmol. 2019;97(8):784–792. doi:10.1111/aos.14112 [CrossRef]
  4. Chen X, Fu Z, Yu J, et al. Prevalence of amblyopia and strabismus in Eastern China: results from screening of preschool children aged 36–72 months. Br J Ophthalmol. 2016;100(4):515–519. doi:10.1136/bjophthalmol-2015-306999 [CrossRef]
  5. Chia A, Roy L, Seenyen L. Comitant horizontal strabismus: an Asian perspective. Br J Ophthalmol. 2007;91(10):1337–1340. doi:10.1136/bjo.2007.116905 [CrossRef]
  6. Holmes JM, Hatt SR, Leske DA. Is intermittent exotropia a curable condition?Eye (Lond). 2015;29(2):171–176. doi:10.1038/eye.2014.268 [CrossRef]
  7. Caltrider N, Jampolsky A. Overcorrecting minus lens therapy for treatment of intermittent exotropia. Ophthalmology. 1983;90(10):1160–1165. doi:10.1016/S0161-6420(83)34412-2 [CrossRef]
  8. Bayramlar H, Gurturk AY, Sari U, Karadag R. Overcorrecting minus lens therapy in patients with intermittent exotropia: should it be the first therapeutic choice?Int Ophthalmol. 2017;37(2):385–390. doi:10.1007/s10792-016-0273-9 [CrossRef]
  9. Yang M, Chen J, Shen T, et al. Clinical characteristics and surgical outcomes in patients with intermittent exotropia: a large sample study in South China. Medicine (Baltimore). 2016;95(5):e2590. doi:10.1097/MD.0000000000002590 [CrossRef]
  10. Wang L, Wu Q, Kong X, Li Z. Comparison of bilateral lateral rectus recession and unilateral recession resection for basic type intermittent exotropia in children. Br J Ophthalmol. 2013;97(7):870–873. doi:10.1136/bjophthalmol-2013-303167 [CrossRef]
  11. Fiorelli VM, Goldchmit M, Uesugui CF, Souza-Dias C. Intermittent exotropia: comparative surgical results of lateral recti-recession and monocular recess-resect. Arq Bras Oftalmol. 2007;70(3):429–432. doi:10.1590/S0004-27492007000300008 [CrossRef]
  12. Na KH, Kim SH. Comparison of clinical features and long-term surgical outcomes in infantile constant and intermittent exotropia. J Pediatr Ophthalmol Strabismus. 2016;53(2):99–104. doi:10.3928/01913913-20160122-05 [CrossRef]
  13. Wu H, Sun J, Xia X, Xu L, Xu X. Binocular status after surgery for constant and intermittent exotropia. Am J Ophthalmol. 2006;142(5):822–826. doi:10.1016/j.ajo.2006.06.045 [CrossRef]
  14. Choi DD, Noh H, Park KA, Oh SY. Survival analysis of adult and children intermittent exotropia using a matched case-control design. Sci Rep. 2019;9(1):575–575. doi:10.1038/s41598-018-38160-8 [CrossRef]
  15. Burian HM, Spivey BE. The surgical management of exodeviations. Trans Am Ophthalmol Soc. 1964;62:276–306.
  16. Archer SM. The effect of medial versus lateral rectus muscle surgery on distance-near incomitance. J AAPOS. 2009;13(1):20–26. doi:10.1016/j.jaapos.2008.09.003 [CrossRef]
  17. Parks MM. Atlas of Strabismus Surgery. Harper & Row; 1983.
  18. Song D-S, Chen Z-J, Qian J. Comparison of bilateral/unilateral lateral rectus recession and unilateral recession-resection for intermittent exotropia: a meta-analysis. Int J Ophthalmol. 2018;11(12):1984–1993.
  19. Riis P. Perspectives on the fifth revision of the Declaration of Helsinki. JAMA. 2000;284(23):3045–3046. doi:10.1001/jama.284.23.3045 [CrossRef]
  20. Abroms AD, Mohney BG, Rush DP, Parks MM, Tong PY. Timely surgery in intermittent and constant exotropia for superior sensory outcome. Am J Ophthalmol. 2001;131(1):111–116. doi:10.1016/S0002-9394(00)00623-1 [CrossRef]
  21. Kanjanawasee P, Praneeprachachon P, Pukrushpan P. Relation between early postoperative deviation and long-term outcome after unilateral lateral rectus recession and medial rectus resection for adult exotropia. Int J Ophthalmol. 2018;11(8):1358–1362.
  22. Oh JY, Hwang JM. Survival analysis of 365 patients with exotropia after surgery. Eye (Lond). 2006;20(11):1268–1272. doi:10.1038/sj.eye.6702091 [CrossRef]
  23. Leow PL, Ko ST, Wu PK, Chan CW. Exotropic drift and ocular alignment after surgical correction for intermittent exotropia. J Pediatr Ophthalmol Strabismus. 2010;47(1):12–16. doi:10.3928/01913913-20100106-04 [CrossRef]
  24. Pineles SL, Ela-Dalman N, Zvansky AG, Yu F, Rosenbaum AL. Long-term results of the surgical management of intermittent exotropia. J AAPOS. 2010;14(4):298–304. doi:10.1016/j.jaapos.2010.06.007 [CrossRef]
  25. Dadeya S, Kamlesh. Long-term results of unilateral lateral rectus recession in intermittent exotropia. J Pediatr Ophthalmol Strabismus. 2003;40(5):283–287. doi:10.3928/0191-3913-20030901-09 [CrossRef]
  26. Bae GH, Bae SH, Choi DG. Surgical outcomes of intermittent exotropia according to exotropia type based on distance/near differences. PLoS One. 2019;14(3):e0214478–e0214478. doi:10.1371/journal.pone.0214478 [CrossRef]
  27. Hamasaki I, Shibata K, Shimizu T, et al. Differences in the stability and amount of postoperative exodrift with age after unilateral lateral rectus muscle recession and medial rectus muscle resection of intermittent exotropia. Acta Med Okayama. 2018;72(5):487–492.
  28. Yam JC, Chong GS, Wu PK, Wong US, Chan CW, Ko ST. Predictive factors affecting the short term and long term exodrift in patients with intermittent exotropia after bilateral rectus muscle recession and its effect on surgical outcome. BioMed Res Int. 2014;2014:482093. doi:10.1155/2014/482093 [CrossRef]
  29. Hatt SR, Gnanaraj L. Interventions for intermittent exotropia. Cochrane Database Syst Rev. 2013;(5):CD003737.
  30. Faridi UA, Saleh TA, Ewings P, Twomey JM. Factors affecting the surgical outcome of primary exotropia. Strabismus. 2007;15(3):127–131. doi:10.1080/09273970701506086 [CrossRef]
  31. Gezer A, Sezen F, Nasri N, Gözüm N. Factors influencing the outcome of strabismus surgery in patients with exotropia. J AAPOS. 2004;8(1):56–60. doi:10.1016/j.jaapos.2003.08.006 [CrossRef]
  32. Trakanwitthayarak S, Patikulsila P. Prognostic factors predicting the surgical outcomes of bilateral lateral rectus recession for patients with concomitant exotropia in Chiang Mai University Hospital. J Med Assoc Thai. 2017;100(1):64–69.
  33. Bukhari S, Qidwai U, Kazi GQ. Success of surgical correction in constant and intermittent exotropias. J Coll Physicians Surg Pak. 2014;24(4):249–251.
  34. Zou D, Casafina C, Whiteman A, Jain S. Predictors of surgical success in patients with intermittent exotropia. J AAPOS. 2017;21(1):15–18. doi:10.1016/j.jaapos.2016.11.018 [CrossRef]
  35. Kushner BJ. Selective surgery for intermittent exotropia based on distance/near differences. Arch Ophthalmol. 1998;116(3):324–328. doi:10.1001/archopht.116.3.324 [CrossRef]
  36. Menon V, Singla MA, Saxena R, Phulijele S. Comparative study of unilateral and bilateral surgery in moderate exotropia. J Pediatr Ophthalmol Strabismus. 2010;47(5):288–291. doi:10.3928/01913913-20091118-07 [CrossRef]
  37. Joyce KE, Beyer F, Thomson RG, Clarke MP. A systematic review of the effectiveness of treatments in altering the natural history of intermittent exotropia. Br J Ophthalmol. 2015;99(4):440–450. doi:10.1136/bjophthalmol-2013-304627 [CrossRef]
  38. Spierer A, Ben-Simon GJ. Unilateral and bilateral lateral rectus recession in exotropia. Ophthalmic Surg Lasers Imaging. 2005;36(2):114–117. doi:10.3928/1542-8877-20050301-06 [CrossRef]
  39. Donahue SP, Chandler DL, Holmes JM, et al. Pediatric Eye Disease Investigator GroupWriting Committee. A randomized trial comparing bilateral lateral rectus recession versus unilateral recess and resect for basic-type intermittent exotropia. Ophthalmology. 2019;126(2):305–317. doi:10.1016/j.ophtha.2018.08.034 [CrossRef]
  40. Kim H, Yang HK, Hwang J-M. Comparison of long-term surgical outcomes between unilateral recession and unilateral recession-resection in small-angle exotropia. Am J Ophthalmol. 2016;166:141–148. doi:10.1016/j.ajo.2016.03.047 [CrossRef]
  41. Spierer O, Spierer A, Glovinsky J, Ben-Simon GJ. Moderate-angle exotropia: a comparison of unilateral and bilateral rectus muscle recession. Ophthalmic Surg Lasers Imaging. 2010;41(3):355–359. doi:10.3928/15428877-20100430-10 [CrossRef]
  42. Burian HM. Exodeviations: their classification, diagnosis and treatment. Am J Ophthalmol. 1966;62(6):1161–1166. doi:10.1016/0002-9394(66)92570-0 [CrossRef]
  43. Deacon BS, Fray KJ, Grigorian AP, et al. Unilateral strabismus surgery in patients with exotropia results in postoperative lateral incomitance. J AAPOS. 2014;18(6):572–575. doi:10.1016/j.jaapos.2014.08.010 [CrossRef]

Patient Characteristics (N = 291)

CharacteristicValue
Gender, no. (%)
  Female148 (51%)
  Male143 (49%)
Age (y), median (range)17 (3 to 83)
Children < 18 years, no. (%)150 (52%)
Exotropia ICD-10, H50.1, no. (%)101 (35%)
Intermittent exotropia ICD-10: H50.3B, no. (%)190 (65%)
Preoperative deviation (PD) in primary position, median (range)
  Distance27 (4.5 to 67)
  Near deviation30 (10 to 75)
Spherical equivalent (D), median (range)
  Right eye0.25 (−9.50 to 8.00)
  Left eye0.25 (−9.50 to 9.75)
Refraction, no. (%)a
  Emmetropia18 (6%)
  Myopia86 (30%)
  Hyperopia148 (51%)
  Antimetropia11 (4%)
Anisometropia ≥ ±2, no. (%)19 (6.5%)
Anesthesia, no. (%)
  General218 (75%)
  Local73 (25%)
No. of operations, no. (%)
  Surgeon 191 (31%)
  Surgeon 2131 (45%)
  Surgeon 319 (6.5%)
  Surgeon 450 (17%)

Comparison of the Characteristics of Patients With Constant vs Intermittent Exotropia

CharacteristicConstant ExotropiaIntermittent ExotropiaP
No.101190
Gender, no. (%).116a
  Female45 (44.6%)102 (53.7%)
  Male56 (55.4%)86 (45.3%)
Age at operation (y), median (range)28 (3 to 83)12.5 (3 to 83)< .001a
Preoperative distance deviation (PD), median (range)33 (4.5 to 65)25 (4.5 to 67)< .001a
Preoperative near deviation (PD), median (range)36.5 (12 to 75)25 (10 to 67)< .001a
Total muscle movement (recession and resection) in mm, median (range)12.5 (4 to 16.5)10 (4 to 15.5)< .001a
Postoperative distance deviation (PD), median (range)6 (−16 to 35)4 (−22 to 35).363b
Postoperative near deviation (PD), median (range)6 (−18 to 45)6 (−30 to 40).155b
Reoperation76.141c
Surgical success, no. (%)71 (70%)152 (80%).923d
Authors

From the Departments of Ophthalmology and Clinical Sciences, Lund University and Skåne University Hospital, Lund, Sweden (RLT, MM, KT, JB); and the Department of Ophthalmology, Sahlgrenska University Hospital, Region Västra Götaland, and the Department of Clinical Neuroscience, Institute of Neuroscience and Physiology, Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden (HBH).

The authors have no financial or proprietary interest in the materials presented herein.

Correspondence: Rannveig Linda Thorisdottir, MD, PhD, Department of Clinical Sciences, Lund University and Skåne University Hospital, BMC F12, 221 84 Lund, Sweden. Email: linda.thorisdottir@med.lu.se

Received: February 26, 2020
Accepted: July 13, 2020

10.3928/01913913-20201007-04

Sign up to receive

Journal E-contents