|Year : 2018 | Volume
| Issue : 3 | Page : 178-182
Outcomes of surgical correction of exotropia in children between 4 to 12 years of age
Department of Ophthalmology, Little Flower Hospital and Research Centre, Angamaly, Kerala, India
|Date of Web Publication||17-Dec-2018|
Nellikunnath House, Pudukad, Thrissur - 680 301, Kerala
Source of Support: None, Conflict of Interest: None
Purpose: This study aims to analyze the outcomes of surgical correction of exotropia in children between 4 to 12 years of age; and the factors associated with favorable surgical outcomes.
Methods: In this prospective observational study, the surgical outcomes of 87 patients between 4 and 12 years of age, who underwent correction for primary exotropia (XT), by a single surgeon, were analyzed at 24 months.
Results: Out of the total 87 patients, 46 (52.87%) were female and 41 (47.13%) were male. The mean age at surgery was 8.83 ± 3.26 years (range 4–12 years). There was a statistically significant reduction in preoperative prism bar cover test (PBCT), with PBCT at day: 1, 1 month, 6 months, 12 months, and 24 months after surgery (P = 0.00, ANOVA). Among the 42 patients analyzed for near stereoacuity (NSA), the change between preoperative and 24 months NSA was not statistically significant (P = 0.55, Chi-square test). Preoperative PBCT for distance was found to be a significant parameter associated with successful motor alignment at 24 months (P = 0.02, logistic regression). Other variables such as gender, age at surgery, preoperative best-corrected visual acuity, preoperative refractive status, and laterality of surgery were not significantly associated with successful motor alignment at 24 months.
Conclusions: Surgical correction of exotropia in children between 4 to 12 years shows satisfactory ocular alignment at 24 months; although there was no significant improvement in NSA in the subgroup analyzed. The preoperative ocular deviation was the only significant factor associated with successful motor outcome at 24 months after surgery.
Keywords: Children, exotropia, surgical outcomes
|How to cite this article:|
Sathyan S. Outcomes of surgical correction of exotropia in children between 4 to 12 years of age. Kerala J Ophthalmol 2018;30:178-82
| Introduction|| |
Exotropia accounts for about 25% of childhood strabismus. Intermittent exotropia (XT) comprises 92% of exotropic deviations among Asian patients below the age of 19 years. Constant exotropia following decompensation of intermittent exotropia results in loss of stereopsis, suppression, and amblyopia. Surgical treatment is indicated in cases with exotropia for >50% of waking hours, to prevent deterioration to constant exotropia, to improve stereoacuity, and for social or cosmetic reasons.
Success rates of surgery for XT in literature are highly variable. This is due to the variability in the follow-up periods and the criteria used for defining success. Factors associated with XT that can possibly influence the prognosis of surgery include type of exotropia, fusional ability, preoperative magnitude of exodeviation, visual acuity, age at diagnosis and surgery, stereopsis, amblyopia, associated abnormalities such as A/V patterns, oblique dysfunction, dissociated vertical deviation, nystagmus, and type of surgical procedures adopted.
Most of the studies analyzing long-term outcomes of exotropia surgery were retrospective chart reviews over a few years, including surgeries performed by different surgeons using different surgical approaches and surgical nomograms. Furthermore, the prospective studies are quite variable in their recommendations on the factors responsible for favorable outcomes.
Hence, we designed this study to analyze the outcomes of surgical correction of XT and the factors governing the outcomes in patients undergoing surgical correction.
The present study aimed to evaluate the outcomes of surgical correction of exotropia in children between 4 to 12 years of age; and to analyze the factors associated with favorable outcomes at 24 months follow-up.
| Methods|| |
In this prospective observational study, 87 patients between 4 and 12 years of age, who underwent surgical correction for exotropia (XT), by a single surgeon, at a tertiary eye care center, from July 2014 to June 2016 were included. Approval for the study was obtained from the Institutional Review Board and the study adhered to the tenets Declaration of Helsinki.
Those patients, between 4 and 12 years of age, diagnosed with XT with a minimum distance exodeviation of ≥16 prism diopters (PD), who underwent surgical correction of strabismus by a single surgeon, with a follow-up at least 24 months postsurgery were included. Those patients with unreliable results in the orthoptic evaluation, neurological deficits, incomitant strabismus, previous strabismus surgery, nystagmus, or any other significant ocular pathology were excluded from the study.
XT was defined as an exodeviation of ≥16 PD in the absence of any other neurologic, paralytic, or ocular disorder.
Successful motor outcome: exodeviations of ≤12 PD or esodeviation ≤6 PD at 24 months after surgery.
Failed motor outcome: exodeviations of ≥13 PD; or esodeviation ≥7 PD at 24 months after surgery.
- Overcorrection: esotropia/phoria ≥7 PD postsurgery
- Undercorrection: exotropia/phoria ≥13 PD postsurgery.
A total of 87 patients who underwent surgical correction of XT by a single surgeon during the study period were included in the analysis. Preoperative factors recorded were as follows: age and sex of the patient, magnitude of misalignment (corneal reflex test and prism bar cover test), associated refractive error and binocular status (TNO steroacuity test, Groningen, The Netherlands). The decision to operate was made by the surgeon based on clinical judgment.
All the surgeries were performed by a single experienced strabismus surgeon, using a conjunctival cul de sac incision. After retracting the conjunctiva and Tenon's capsule, the muscle was exposed, and the required amount of recession/resection was performed using customized surgical normograms. The muscle was anchored to the sclera using partial thickness bites with absorbable sutures. The conjunctiva was closed with absorbable sutures. Intra-operative parameters recorded were as follows: laterality of surgery, the amount of recession/resection performed.
Postoperative parameters recorded were as follows: alignment at day-1, 1 month, 12 months, and 24 months (corneal reflex test and prism bar cover test), binocular status (TNO steroacuity test), refraction, and repeat surgeries if any.
Patients were classified as successful motor alignment or failed motor alignment according to the operational definitions used and the results were analyzed. Preoperative risk factors for poor outcomes at 24 months were analyzed.
The data were analyzed using SPSS software for Windows (version 20.0, Chicago, IL, USA). Preoperative ocular alignment and alignment at postoperative day 1, months 1, 12 and 24 were analyzed by repeated measures ANOVA. Improvement in near stereoacuity (NSA) was compared using Chi-square test. Preoperative factors influencing the ocular alignment at 24 months including, age at surgery, the age of onset of deviation, associated refractive errors, the angle of distance deviation (in PD), preoperative binocular vision status were analyzed using logistic regression analysis. A value of P ≤ 0.05 was considered to be statistically significant.
| Results|| |
A total of 87 patients who underwent surgical correction of exotropia between 4 to 12 years of age were included in the analysis. Forty-six (52.87%) were female and 41 (47.13%) were male. The mean age at surgery was 8.83 ± 3.26 years (range 4–12 years). The mean preoperative prism bar cover test (PBCT) was 34.32 ± 9.13 PD. Preoperative refraction showed emmetropia in 38 (43.68%), myopia in 7 (8.04%), hypermetropia in 5 (5.75%) and astigmatism in 37 (42.53%). Fifty-two (67.53%) had intermittent exotropia and 25 (32.47%) constant exotropia. Sixty-eight patients (78.16%) underwent bilateral lateral rectus recession and 19 patients (21.18%) underwent the unilateral recess-resect procedure.
There was a statistically significant reduction in preoperative PBCT, with PBCT at day: 1, 1 month, 6 months, 12 months, and 24 months after surgery (P = 0.00, one-way ANOVA) [Figure 1].
|Figure 1: Comparison of preoperative ocular deviation with follow up visits|
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Preoperative NSA could be reliably assessed only in 77 patients. Out of these patients, the binocular single vision was absent in 22, gross stereopsis was present in 12, NSA between 550 and 240 s of the arc was present in 18 and NSA between 120 and 60 s of arc was present in 25 patients [Figure 2].
Among the 42 patients with NSA ≤550 s of arc, at 24 months, improvement by at least one unit was seen in 24 (57.14%), remained the same in 12 (42.86%). The improvement in NSA in this subgroup was not statistically significant (χ2 = 0.35, P = 0.55).
Out of the total of 87 patients, 75 (86.21%) were assigned to the successful motor outcome group (SG), and 12 (13.79%) to the failed motor outcome group (FG) [Figure 3]. Among the FG, 9 (10.34%) had residual exodeviation 17.50 ± 3.50 PD at 24 months follow-up. Six of these patients had good cosmetic alignment after the initial surgery, while three had residual exodeviation. These three patients underwent second surgery after 6–8 months and had satisfactory alignment at 24 months. Out of the total 87 patients, 3 (3.45%) developed small consecutive esodeviation (7.00 ± 1.50 PD). As there was no drop in visual acuity or ocular alignment even at 24 months, no further procedures were done on these patients.
Logistic regression analysis was used to analyze the relationship between surgical outcome at 24 months month postsurgery and the preoperative parameters including gender, age at surgery, preoperative best-corrected visual acuity (BCVA), preoperative refractive status, preoperative PBCT for distance, and laterality of surgery. The preoperative PBCT for distance was found to be a significant parameter associated with successful motor alignment at 24 months (P = 0.02). Other variables did not have significant association with successful motor alignment at 24 months [Table 1].
|Table 1: Logistic regression analysis for parameters associated with successful outcome at 24 months|
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| Discussion|| |
The present study reveals outcomes of surgical correction of XT done by a single surgeon at a follow-up period of 24 months. The results show significant improvement in motor alignment (P = 0.00), starting at the first postoperative day and maintained through further follow-ups up to 24 months. The subset of patients analyzed for improvement of NSA did not show a statistically significant difference between pre- and post-surgical values (P > 0.05).
Surgical success rates in XT are quite variable ranging from 38% to 91.6%,,,,, This variability in literature is due to the differences in surgical approaches, normograms and the criteria used for defining “success” and “failure.” Our failure rate (cut-off criteria: Exodeviations of ≥13 PD or esodeviation ≥7 PD at 24 months follow-up) was 14.2% and was comparable to previous studies.,,,,
Although undercorrections and overcorrections are cited as causes of the failed surgical outcome, Burke have reported that recurrence of XT is the more common cause of failure than overcorrections. Overcorrections have been reported ranging from 1.5% to 27%. and may more frequently be seen over longer periods of follow up., The present study also showed more of undercorrections (10%) than overcorrections (4%).
Adams et al. have reported significant improvement in stereoacuity following surgical correction of intermittent exotropia. However, the subset of patients analyzed in the present sample did not show significant improvement in stereoacuity (P > 0.05). This may be because in addition to intermittent exodeviations, constant exotropias were also included in this study. This would have resulted in marked heterogeneity regarding fusional control and sensory status pre-operatively.
Most of the patients in the present study were emmetropes (43.68%) or myopic astigmats (42.53%). Simple myopia (8.04%) and simple hypermetropia (5.75%) were relatively less in our study group. This was in lines with the findings by Mohney and Huffaker who reported a normal distribution of refractive errors similar to that of the general population in patients with IXT. Other studies have reported a higher prevalence of myopia in children with X(T) compared to the general population; and a preponderance of myopia (43%) in children with X(T).
In the present study, the initial preoperative deviation for distance was the only significant factor associated with successful motor outcome at 24 months (P = 0.02). Other factors such as age at surgery (P = 0.39), gender (P = 1.00), preoperative refractive status (P = 0.45), and preoperative BCVA (P = 0.94) were not significantly associated with successful motor outcome at 24 months. Scott et al. have enumerated that preoperative deviation, the difference between distance and near deviations and age at surgery were significant variables influencing the postoperative alignment in patients with XT. Pineles et al., in their study of 50 patients re-examined 10 years after initial surgery concluded that patients with anisometropia, lateral incomitance, and immediate postoperative undercorrection were at increased risk for poor outcomes requiring reoperations. Saleem et al. concluded that preoperative deviation was one of the strongest predictors for favorable surgical outcome. Similar observations were made by other authors also.,,, One study states that age of initial deviation is not a significant determinant of the surgical outcome at 2 years. Age at surgery was found to be a significant factor affecting the surgical outcome by some authors;,, whereas some others concluded that age at surgery does not significantly influence the outcome of surgical correction.,,,,
Some authors have suggested initial overcorrection as a factor for favorable long-term outcomes. However, the present study did not aim at initial overcorrection and therefore did not attempt to analyze this observation. However, none of our patients had esodeviation on the first postoperative day and at further follow-up visits showed satisfactory alignment. Hence, we assume that initial overcorrection is not necessary for favorable long-term motor alignment.
Some authors have reported that patients with good preoperative residual stereoacuity were more likely to have favorable surgical outcomes. This factor could not be ascertained from our study as the data for preoperative binocular status could not be obtained reliably from all the patients, and as our sample was heterogenpous with regard to their sensory status because intermittent and constant exodeviations were included. However in the group assigned as “failed motor outcome,” preoperative PBCT was the only factor associated with failure at 1 year; preoperative NSA was not a significant predictor of failure (P = 0.56).
Merits of the study include its prospective observational design, standardized sample selection and analysis of factors responsible for the surgical outcome in the total sample and in the subgroup with “failure motor outcome.”
The results of this study have several limitations. First, selection bias could have occurred, as only patients who were followed up for at least 2 years were included. Patients showing satisfactory results were less likely to return to the clinic, and those showing unfavorable results were more likely to have been followed up longer. Furthermore, the follow-up period is relatively short.
In spite of its limitations, the present study shows that the motor outcomes after surgical correction of primary exotropia in children between 4 to12 years are satisfactory at 24 months. However, the subgroup analysis failed to demonstrate significant improvement in sensory status following surgical correction of exodeviations. Preoperative ocular deviation for distance was the only significant factor associated with favorable motor outcome at 24 months postsurgery. This indicates that elimination of factors likely to cause errors in the determination of preoperative deviation is important in improving the predictability of surgery for exotropia.
| Conclusions|| |
Surgical correction of exotropia in children between 4 and 12 years shows satisfactory ocular alignment at 24 months; though there was no significant improvement of sensory status in the subgroup analyzed. Preoperative ocular deviation for distance was the only significant factor associated with favorable motor outcome at 24 months after surgery.
Other factors such as age, gender, preoperative visual acuity, refraction, and preoperative sensory status were not significant factors for favorable surgical outcome.
The author would like to thank Dr. Ayisha Suhana and Dr. Jyothi R for rendering help in data entry.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]