The patients in this study showed significant myopic progression during follow-up regardless of surgical correction, which is in accordance with previous studies. Ekdwai et al.10 reported a relationship between intermittent exotropia and myopic progression, in which 91.1% patients with intermittent exotropia showed myopia during the 20-year follow-up. Moreover, Shin et al.18 also reported a significant myopic progression in 210 early school-aged children.
In this study, there was no significant difference in myopic progression according to bilateral lateral rectus recession. Some previous studies reported similar results to this study. Ekdwai et al.10 compared the myopic progression of 54 patients with intermittent exotropia who underwent bilateral rectus recession and 81 patients who did not. In this report, there was no significant difference between them. Shin et al.18 also compared the myopic progression in 86 patients who underwent surgery and 54 patients who did not and reported that there was no significant difference between them. On the other hand, Park et al.17 reported different results. They compared both eyes of patients who received unilateral lateral rectus recession. In this retrospective report, the low myopia group showed significantly more rapid myopic progression in the operated eyes than in the un-operated ones. However, similar to our results, there was no significant difference in patients with refractive errors other than low myopia.
On the other hand, patients who underwent surgery showed significantly more cylindrical change than patients who did not undergo surgery. These results are similar to those of previous studies that reported a significant increase in cylinder after receiving surgery17, 21,22,23. A little difference was the shorter duration of cylindrical change. Those studies showed shorter than 6 months of cylindrical change; however, it was maintained for almost 1 year in this study.
Our study also performed additional analyses on patients who underwent surgery. At first, we compared the myopic progression of patients aged around 6 years. In our study, there was a significant difference in the rate of myopic progression between early childhood and school-aged children. This was superficially in accordance to a previous study by Tricard et al.24, wherein they reported that 7–9 and 10–12 year-old children showed faster progression. However, we also found different results through a more detailed analysis. The components of SE, sphericity, and cylinder showed different results. Unlike SE, sphericity was not different between the two groups. The two results are contradictory in terms of myopic progression, and this is because the change in SE was influenced by the cylinder. The cylinder had decreased during the last visit in the early childhood group, which might have increased the gap in SE between the two groups. The reason might be the decrease in astigmatism over years due to the emmetropization of children25. At the same time, because the operation amount of patients in the early childhood group was significantly larger, surgery-induced astigmatism should have been increased more than in the school-aged group. Hence, further evaluation about the cylindrical change by age is needed.
Second, patients who experienced a recurrence of more than 10 PD after surgery were compared with patients who did not have recurrence, and there was no significant difference in myopic progression. Based on previous studies about accommodation and myopic progression12, 13, 26, the increased demand for accommodative convergence after recurrence might have caused more myopic progression than in patients who showed orthotropia after surgery. However, our study showed no significant difference, which is in accordance with a recent report that showed skepticism about the relevance of accommodation and myopic progression27. However, in terms of progression rate, the group with faster rate had significantly more recurrence after surgery. In multivariable analysis, recurrence showed significant positive association (Table 5). These results partially conflict with each other. However, as shown in Table 3, the rate of myopic progression was faster in the recurrent group, although it was not significant. Thus, it may be difficult to state that there is no correlation between myopic progression and recurrence. For clearer results, further evaluation is needed.
Nevertheless, this study still has some limitations. First, this was a retrospective study; hence, there was little difference in the last follow-up period among the patients. Second, the refractive errors in all patients were measured only using manifest refraction. In general, the gold standard for refractive measurement in children is cycloplegic refraction. Moreover, previous studies reported some difference between cycloplegic and non-cycloplegic refraction. This difference is especially severe in patients with hyperopia and emmetropia; however, in the case of patients with myopia, the difference was smaller: non-cycloplegic refraction shows 0.09–0.25 D more myopia18, 28,29,30. The more important point is that this study aimed to confirm changes in the amount of myopia. Since the entire refraction test was conducted without cycloplegia in this study, there would be no problem with the reliability of the results. Third, although the total number of participants in this study was larger than that of previously published studies, the number of patients who did not undergo surgery was relatively smaller compared to those who received surgery. Fourth, other factors that may affect the progression of myopia—outdoor activities, degree of near work, and family history—were not reflected in the study. One example of is axial length, which has been shown to have a high correlation with myopia in many studies. However, due to the retrospective design of our study, axial length was not included for analysis. If future research includes an analysis of both refractive error and biometric data such as axial length, the correlation would be more accurate. Lastly, since the purpose of this study was to confirm the effect of surgery, one disadvantage is that the entire follow-up period was relatively shorter than others. However, if the observation period was set for a longer time, other environmental factors besides surgery would have greater impact, and the reliability of the results would be further reduced.
Our study results indicate that bilateral lateral rectus recession in patients with intermittent exotropia do not affect myopic progression. Moreover, there was no significant change in myopic progression by recurrence and overcorrection after bilateral lateral rectus recession. However, careful follow-up is still needed because rapid myopic progression can be expected in patients with recurrence.