Based on the difference between the distance and near measurements of deviation, intermittent exotropia is classified into basic, pseudodivergence excess, true divergence excess, and convergence insufficiency types. Basic exotropia refers to exodeviation that is approximately equal at distance and near fixation.1 There are numerous studies on surgical outcomes of intermittent exotropia. Some authors2–6 analyzed their results of surgery in relation to the type of intermittent exotropia, including basic exotropia. Kushner3 and Burian7 suggested that patients with basic intermittent exotropia should be treated with a recess–resect procedure. To our knowledge, there are only a few, exclusive studies8–12 on the surgical outcome of basic intermittent exotropia after unilateral recession–resection. Moreover, the minimum postoperative follow-up in these studies ranges from 6 months to 5 years. The purpose of this study was to report the long-term motor and sensory outcomes after unilateral lateral rectus recession–medial rectus resection for basic intermittent exotropia in patients who had a minimum postoperative follow-up of 10 years.
Patients and Methods
The medical records of consecutive patients at our tertiary care facility who had undergone unilateral lateral rectus recession–medial rectus resection for basic intermittent exotropia between 1998 and 2008 by a single surgeon (KM) were reviewed retrospectively. We included patients who had a minimum postoperative follow-up of 10 years. The study was approved by our institutional review board and complied with the tenets of the Declaration of Helsinki. We diagnosed a patient as having basic intermittent exotropia if the difference between the distance and near exodeviation was less than 10 prism diopters (PD). Patients with previous strabismus surgery, exotropia greater than 50 PD, restricted ocular movements, and dissociated vertical deviation were excluded. All baseline and postoperative examinations were performed by one unmasked investigator (KM). The following data were collected: age at presentation, age at onset of strabismus (told by the parents), visual acuity, cycloplegic refraction, deviations at near and distance, presence or absence of fusion and stereopsis, age at surgery, and follow-up time. Duration of strabismus was calculated as the difference between age at surgery and age at onset of strabismus.
Visual acuity was assessed using a Snellen distance visual acuity chart in older patients and binocular fixation pattern in younger patients. Amblyopia was diagnosed when there was a difference of two or more Snellen lines between the best corrected visual acuity of the two eyes in older patients and a lack of alternate fixation on cover-uncover testing in younger patients. Cycloplegic refractions were performed after instillation of atropine 1% twice a day for 3 days in children 10 years of age and younger and after three instillations of cyclopentolate 1% in children older than 10 years. The spherical equivalent refractive error was calculated as the sum of the sphere and half of the cylinder power. Anisometropia was defined as a difference of 1.50 diopters (D) or greater in the spherical equivalent refractive error of both eyes. Amblyopia was treated with full-time occlusion of the non-amblyopic eye. In older patients, occlusion treatment was continued until visual acuity of the amblyopic eye became equal to that of the non-amblyopic eye, and was discontinued if there was no improvement or no further improvement in visual acuity for 3 consecutive months. In younger patients, occlusion treatment was continued until there was an alternate fixation on cover-uncover test, and it was discontinued if a fixation preference persisted after 3 months of occlusion treatment. Surgery was performed after amblyopia was treated.
Ocular deviations were measured at near and distance fixation using the prism and alternate cover test. Sensory status was assessed using the Worth 4-dot test and the TNO stereotest (Lameris Ootech B.V.). Peripheral binocular single vision was diagnosed if the patient had binocular single vision response on the Worth 4-dot test at either near (33 cm) or distance (6 m) but no demonstrable stereo-acuity on the TNO test.
Unilateral lateral rectus muscle hang-back recession combined with medial rectus muscle resection was performed for the largest exotropic deviation. No intentional overcorrection was planned. The amount of surgery was based on the same standard table of surgical dosage.13 Any associated vertical pattern with overaction of the oblique muscles was treated concurrently with the weakening procedure for the corresponding oblique muscles.
Surgical success was defined as alignment within 10 PD of orthophoria at both distance and near fixation. Postoperative exotropia greater than 10 PD or esotropia greater than 10 PD at any time during the follow-up was considered a failure. Recurrence of intermittent exotropia was defined as an intermittent exodeviation greater than 10 PD at distance and/or near fixation at any time after an initial successful alignment.
Data were analyzed using the t test, Fisher exact test, Z test for proportions, and chi-square test using the SPSS software (version 23.0; SPSS, Inc) for Windows. Kaplan-Meier survival analysis was used to determine the cumulative probability of surgical success at various follow-up visits. A P value of less than .05 was considered statistically significant.
A total of 445 patients with basic intermittent exotropia underwent unilateral lateral rectus recession–medial rectus resection during the study period. Of these patients, 41 (26 females [63%]) had a minimum postoperative follow-up of 10 years and were included in the study. The mean patient age was 6.07 ± 2.96 years (range: 3 to 17 years) at presentation, 2.61 ± 2.57 years (range: 2 months to 10 years) at onset of strabismus, and 6.75 ± 3.15 years (range: 3 to 18 years) at surgery. The mean duration of strabismus was 4.14 ± 2.58 years (range: 6 months to 10 years).
Preoperatively, the mean deviation was 29.0 ± 7.2 PD (range: 20 to 50 PD) at near and 29.1 ± 8.3 PD (range: 20 to 50 PD) at distance. On cycloplegic refraction, 21 of 41 patients (51%) had no refractive error and 20 (49%) had a mean spherical equivalent refractive error of +0.46 ± 2.00 D (range: −1.00 to +3.00 D) in the right eye and +0.33 ± 2.32 D (range: − 0.50 to +6.50 D) in the left eye. There was no significant difference in the mean spherical equivalent refractive error between right and left eyes (P = .86).
Of the 41 patients, 4 (10%) had anisometropic amblyopia. Amblyopic eyes had an initial best corrected visual acuity of 20/40 and 20/120 (2 patients, each). After amblyopia treatment, 3 of 4 patients (75%) had an improvement in visual acuity. The two patients with a visual acuity of 20/40 improved to 20/20 and 20/30 (one patient, each), 1 of 2 patients with a visual acuity of 20/120 improved to 20/60, and the other patient had no improvement. Preoperative Snellen visual acuity was recorded in 39 patients. Of these, visual acuity was 20/20 to 20/30 in 36 (92%) and 20/40 to 20/120 in 3 (8%). One patient (2%) had a V-pattern and bilateral inferior oblique overactions and underwent recession of these muscles. The mean postoperative follow-up period after the initial surgery was 13.28 ± 3.27 years (range: 10 to 23 years).
Figure 1 shows the incidence of surgical success at different follow-up intervals. Overall, 19 of 41 patients (46%) had surgical success at their most recent follow-up. Kaplan-Meier survival analysis showed probabilities of surgical success of 59% at 5 years, 46% at 10 years, and 31% at 15 years postoperatively (Figure 2).
Incidence of surgical success at different follow-up intervals. The number of patients appears above the bar.
Cumulative probability of surgical success at various follow up intervals.
Surgical success at the most recent follow-up in relation to the preoperative characteristics is presented in Table 1. There was no statistically significant difference in the surgical success in relation to age at onset of strabismus (≤ 3 vs > 3 years, P = .31), age at surgery (≤ 7 vs > 7 years, P = 0.26), duration of strabismus (≤ 5 vs > 5 years, P = .48), mean near and distance deviations (≤ 30 vs > 30 PD, P = .76 and P = .48, respectively), presence of stereopsis (P = .27), and amblyopia (P = .61). Seventeen of the 36 patients (47%) with a preoperative visual acuity of 20/20 to 20/30 had surgical success compared with 1 of 3 patients (33%) with 20/40 to 20/120 (P = .64). Twenty-one patients (51%) had orthophoria and 20 (49%) had esotropia (≤ 10 PD, 18 [44%]; > 10 PD, 2 [5%]) on the first postoperative day. Ten of 21 patients (48%) with orthophoria had surgical success compared to 9 of 20 patients (45%) with esotropia (P = .86). Eleven of 20 patients with esotropia on the first postoperative day had more than 10 PD of exotropia at the most recent follow-up.
Surgical Success in Relation to the Preoperative Characteristics
Preoperative and postoperative binocular vision records were available for 34 patients. Preoperatively, 4 patients (12%) did not have binocular single vision, 7 (21%) had peripheral binocular single vision, and 23 (67%) had stereopsis (60 seconds of arc [arcsec] = 16; 120 arcsec = 2; 240 arcsec = 5). Three of 4 patients (75%) without binocular single vision had surgical success at the most recent follow-up visit compared to 3 of 7 patients (43%) with peripheral binocular single vision (P = .26). Of the 23 patients with stereopsis, 8 (35%) had surgical success compared to 3 of 7 patients (43%) with peripheral binocular single vision (P = .70). At the most recent follow-up, 1 patient (3%) did not have binocular single vision, 8 (23%) had peripheral binocular single vision, and 25 (74%) had stereopsis (60 arcsec = 24; 240 arcsec = 1). Postoperatively, 3 of 4 patients (75%) without binocular single vision achieved peripheral binocular single vision. None of the 4 patients without binocular single vision achieved stereopsis, whereas 3 of 7 patients (43%) with peripheral binocular single vision achieved stereopsis (60 arcsec, P = .02). Five of 7 patients (71%) with a preoperative stereoacuity of 120 to 240 arcsec improved to a stereoacuity of 60 arcsec after surgery. One patient with a preoperative stereoacuity of 240 arcsec lost stereopsis and deteriorated to peripheral binocular single vision after surgery. This patient had an unsuccessful surgical result (> 10 PD exotropia). Nineteen of 25 patients (76%) who were 7 years or younger at surgery achieved stereopsis compared to 6 of 9 patients (67%) who were older than 7 years (P = .60). Twenty-two of 24 patients (92%) with 5 or fewer years of strabismus duration achieved stereopsis compared to 3 of 10 patients (30%) with more than 5 years of strabismus duration (P = .001). Thirty-three patients had records of both preoperative Snellen visual acuity and the most recent binocular vision status. Visual acuity was 20/20 to 20/30 in 32 of 33 patients (97%) and 20/40 in 1 patient (3%). Of the 32 patients with a visual acuity of 20/20 to 20/30, 23 (72%) had stereopsis compared to 9 (28%) with peripheral binocular single vision or without binocular single vision (P = .0001). One patient with a visual acuity of 20/40 had stereopsis.
Overall, 22 of 41 patients (54%) had recurrence of intermittent exotropia at a mean age of 4.18 ± 2.99 years (range: 2 months to 11 years) after the first surgery. Recurrence occurred within 2 years in 7 patients (17%), within 5 years in 16 patients (39%), and after 5 years in 6 patients (15%). Of the 22 patients with recurrent exotropia, 5 (23%) underwent a second surgery (recession–resection procedure in the other eye) at a mean 9.5 years (range: 2 to 18 years) after the first surgery.
The results of unilateral lateral rectus muscle recession–medial rectus muscle resection for basic intermittent exotropia in various studies3,8–12 are not comparable due to the differences in the criteria used to define surgical success and variations in follow-up periods. The postoperative success rates reported range from 82% at 1 year3 to 37% at 3 years.11 Bang et al9 found a 74.2% success rate (esophoria/esotropia ≤ 8 PD to exophoria/exotropia ≤ 8 PD) at 1 year and 41.9% at 5 years after unilateral recession–resection for basic intermittent exotropia, whereas Pineles et al5 found excellent motor outcome (intermittent exotropia of 8 PD or less) in 65% of their patients with basic intermittent exotropia with a minimum postoperative follow-up of 10 years. However, Pineles et al did not analyze their results for unilateral recession–resection separately.
After comparing the surgical results of bilateral lateral rectus recession with unilateral recession–resection for intermittent exotropia, Choi et al14 found a success rate of 58.2% in the bilateral lateral rectus recesssion group and 27.4% in the recession–resection group at an average 3.8 years of follow-up. In the current study, we had surgical success (alignment within 10 PD of orthophoria) in 46% of our patients with a minimum postoperative follow-up of 10 years. Postoperatively, the probability of surgical success declined from 59% at 5 years to 31% at 15 years in our patients. This decline in success rate over time in basic intermittent exotropia is similar to that reported in intermittent exotropia in general.15
Several investigators have reported on the role of various preoperative characteristics on the surgical outcome of intermittent exotropia in general, and not specifically in its basic type. Pratt-Johnson et al16 concluded that surgery before 4 years of age was a significant factor for obtaining good alignment in children with intermittent exotropia. Other investigators did not find age at onset of strabismus,17,18 age at surgery,6,17–19 preoperative size of deviation,6,17–19 duration of strabismus,18 and stereopsis17,20 predictive of motor success after surgery for intermittent exotropia. We also did not find the effect of these preoperative characteristics on the motor outcome in our patients with basic intermittent exotropia. Further, a preoperative absence of binocular single vision or the presence of peripheral binocular single vision also had no effect on surgical success. Our observations indicate that there are no preoperative characteristics specific to the basic intermittent exotropia that can affect the motor outcome after surgery. Park and Kim21 found that amblyopic patients had a greater tendency toward exodrift after surgery for intermittent exotropia. Although few patients in our study had amblyopia, we found that it did not have a significant effect on surgical outcomes.
There is no agreement on the importance of initial postoperative overcorrection for long-term alignment for intermittent exotropia. Some investigators22,23 reported that an overcorrection of an average 10 PD at the first postoperative week was associated with a more favorable long-term surgical outcome in patients with intermittent exotropia, whereas others17,24 did not find such an association. We did not find initial postoperative overcorrection to be a predictor for the long-term motor success in patients with basic intermittent exotropia.
In our study, 75% of patients without binocular single vision preoperatively improved to peripheral binocular single vision, but no patients achieved stereopsis after surgery. These observations indicate that a preoperative absence of binocular single vision in patients with basic intermittent exotropia may improve to peripheral binocular single vision, but it carries a poor prognosis for the recovery of stereopsis. In contrast, approximately 45% of our patients with peripheral binocular single vision preoperatively achieved stereopsis, indicating that the presence of peripheral binocular single vision does not preclude recovery of stereopsis. Feng et al25 found that near stereoacuity significantly improved after intermittent exotropia surgery. We also had a similar observation. Abroms et al26 concluded that patients who had motor realignment before 7 years of age had significantly greater chances of having a postoperative stereoacuity greater than 60 arcsec. We did not find any such correlation. Our patients with less than 5 years of strabismus duration had significantly greater chances of achieving stereopsis, as also reported by Abroms et al.26
We found an overall recurrence rate of 54% at a mean of approximately 4 years after the first surgery for basic intermittent exotropia, which is similar to that reported in intermittent exotropia in general4,24 and basic intermittent exotropia.4 Bang et al9 found that recurrence after surgery for basic intermittent exotropia most commonly occurred between 2 and 3 years after bilateral lateral rectus recession, but they also observed continuous recurrences after unilateral recession–resection. We found recurrence in 17% of our patients within 2 years of surgery, which has also been reported in patients with intermittent exotropia in general.24 Approximately 40% of our patients had recurrence within 5 years after first surgery.
A poor long-term surgical outcome of intermittent exotropia prompted several investigators to study the natural course of untreated intermittent exotropia. Holmes et al27 reported a cure rate of 30% in surgically managed and 12% in conservatively managed intermittent exotropia at 5 years of follow-up. Only a small proportion of their patients had a long-term cure after an average 7 years of follow-up. Mohney et al28 found that the intermittent exotropia control, stereoacuity, and magnitude of deviation remained stable or improved slightly over 3 years of follow-up. Chia et al29 reported that half of their patients with intermittent exotropia eventually had surgery and the remaining half had a relatively stable deviation after 3 years of follow-up. Kwok et al30 reported that approximately one-third of Chinese children with intermittent exotropia deteriorated in the control of deviation over a 3-year period. In a study on long-term observations on unoperated intermittent exotropia, Hiles et al31 concluded that all intermittent exotropias do not deteriorate with the passage of time because some improve in both the quality and quantity of the deviation, and surgical interference may be deferred in small and moderate degrees of intermittent exotropia unless deterioration becomes evident.
This study had some limitations. It was a retrospective study and the postoperative follow-up was not uniform. Also, age at onset of strabismus was provided by the parents and could have been inaccurate. Therefore, the length of strabismus duration could be unreliable. Amblyopia was diagnosed as a lack of alternate fixation in younger patients, which may have been due to poor cooperation as opposed to true amblyopia. One unmasked investigator performed all preoperative and postoperative examinations; therefore, some element of bias in the measurement of postoperative deviation cannot be ruled out. Further, our measurement of esotropia on the first postoperative day could be inaccurate because of limited patient cooperation due to discomfort.
- von Noorden GK. Binocular Vision and Ocular Motility: Theory and Management of Strabismus, 5th ed. Mosby; 196:342.
- Zibrandtsen P, Rindziunski E, Gregersen E. Ten years follow-up of surgery for intermittent exotropia. Acta Ophthalmol (Copenh). 1986;64(4):374–378. doi:10.1111/j.1755-3768.1986.tb06938.x [CrossRef]
- 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]
- 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. doi:10.1371/journal.pone.0214478 [CrossRef]
- 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]
- Chia A, Seenyen L, Long QB. Surgical experiences with two-muscle surgery for the treatment of intermittent exotropia. J AAPOS. 2006;10(3):206–211. doi:10.1016/j.jaapos.2005.11.015 [CrossRef]
- 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]
- Yuksel D, Spiritus M, Vandelannoitte S. [Symmetric or asymmetric surgery for basic intermittent exotropia]. Bull Soc Belge Ophtalmol. 1998;268:195–199.
- Bang SP, Cho SY, Lee SY. Comparison of long-term surgical outcomes of two-muscle surgery in basic-type intermittent exotropia: bilateral versus unilateral. Korean J Ophthalmol. 2017;31(4):351–359. doi:10.3341/kjo.2016.0071 [CrossRef]
- 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]
- Donahue SP, Chandler DL, Holmes JM, et al. Pediatric Eye Disease Investigator Group, Writing 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]
- Sun Y, Zhang T, Chen J. Bilateral lateral rectus recession versus unilateral recession resection for basic intermittent exotropia: a meta-analysis. Graefes Arch Clin Exp Ophthalmol. 2018;256(3):451–458. doi:10.1007/s00417-018-3912-1 [CrossRef]
- Burk MJ. Intermittent exotropia. In: Nelson LB, Wagner RS, eds. International Ophthalmology Clinics, vol 25. Brown; 1985:53–68. doi:10.1097/00004397-198502540-00006 [CrossRef]
- Choi J, Chang JW, Kim SJ, Yu YS. The long-term survival analysis of bilateral lateral rectus recession versus unilateral recession-resection for intermittent exotropia. Am J Ophthalmol. 2012;153(2):343–351.e1. doi:10.1016/j.ajo.2011.06.024 [CrossRef]
- Lee JY, Ko SJ, Baek SU. Survival analysis following early surgical success in intermittent exotropia surgery. Int J Ophthalmol. 2014;7(3):528–533.
- Pratt-Johnson JA, Barlow JM, Tillson G. Early surgery in intermittent exotropia. Am J Ophthalmol. 1977;84(5):689–694. doi:10.1016/0002-9394(77)90385-3 [CrossRef]
- Pineles SL, Deitz LW, Velez FG. Postoperative outcomes of patients initially overcorrected for intermittent exotropia. J AAPOS. 2011;15(6):527–531. doi:10.1016/j.jaapos.2011.08.007 [CrossRef]
- Lee J, Kim H, Chung J. A comparison of surgical results between sensory changes in intermittent exotropia. Ann Ophthalmol. 1997;29:96–100.
- Ing MR, Nishimura J, Okino L. Outcome study of bilateral lateral rectus recession for intermittent exotropia in children. Ophthalmic Surg Lasers. 1999;30(2):110–117.
- Beneish R, Flanders M. The role of stereopsis and early postoperative alignment in long-term surgical results of intermittent exotropia. Can J Ophthalmol. 1994;29(3):119–124.
- Park KH, Kim SY. Clinical characteristics of patients that experience different rates of exodrift after strabismus surgery for intermittent exotropia and the effect of the rate of exodrift on final ocular alignment. J AAPOS. 2013;17(1):54–58. doi:10.1016/j.jaapos.2012.10.014 [CrossRef]
- Lee HJ, Kim SJ, Yu YS. Long-term outcomes after same amount of bilateral rectus muscle recession for intermittent exotropia with the same angle of deviation. J Pediatr Ophthalmol Strabismus. 2018;55(5):319–325. doi:10.3928/01913913-20180329-02 [CrossRef]
- Ahn JH, Paik H. Long-term surgical outcomes of initial postoperative overcorrection in adults with intermittent exotropia. Korean J Ophthalmol. 2018;32(3):228–233. doi:10.3341/kjo.2017.0064 [CrossRef]
- Choi J, Kim SJ, Yu YS. Initial postoperative deviation as a predictor of long-term outcome after surgery for intermittent exotropia. J AAPOS. 2011;15(3):224–229. doi:10.1016/j.jaa-pos.2010.12.019 [CrossRef]
- Feng X, Zhang X, Jia Y. Improvement in fusion and stereopsis following surgery for intermittent exotropia. J Pediatr Ophthalmol Strabismus. 2015;52(1):52–57. doi:10.3928/01913913-20141230-08 [CrossRef]
- 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]
- 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]
- Mohney BG, Cotter SA, Chandler DL, et al. Pediatric Eye Disease Investigator GroupWriting Committee. Three-year observation of children 3 to 10 years of age with untreated intermittent exotropia. Ophthalmology. 2019;126(9):1249–1260. doi:10.1016/j.ophtha.2019.01.015 [CrossRef]
- Chia A, Seenyen L, Long QB. A retrospective review of 287 consecutive children in Singapore presenting with intermittent exotropia. J AAPOS. 2005;9(3):257–263. doi:10.1016/j.jaapos.2005.01.007 [CrossRef]
- Kwok JJ, Chong GS, Ko ST, Yam JC. The natural course of intermittent exotropia over a 3-year period and the factors predicting the control deterioration. Sci Rep. 2016;6(1):27113. doi:10.1038/srep27113 [CrossRef]
- Hiles DA, Davies GT, Costenbader FD. Long-term observations on unoperated intermittent exotropia. Arch Ophthalmol. 1968;80(4):436–442. doi:10.1001/archopht.1968.00980050438006 [CrossRef]
Surgical Success in Relation to the Preoperative Characteristics
|Variable||No. of Patients||Success (%)||P|
|Age at onset of strabismus (y)|
| ≤ 3||31||13 (42)||.31a|
| > 3||10||6 (60)|
|Age at surgery (y)|
| ≤ 7||29||15 (52)||.33b|
| > 7||12||4 (33)|
|Duration of strabismus (y)|
| ≤ 5||28||14 (50)||.48a|
| > 5||13||5 (38)|
| ≤ 30||29||13 (45)||.76a|
| > 30||12||6 (50)|
| ≤ 30||28||14 (50)||.48a|
| > 30||13||5 (38)|
| Yes||23||8 (35)||.27a|
| No||11||6 (54)|
| Yes||4||1 (25)||.61b|
| No||37||18 (49)|