Our study evaluated the largest series of patients with basic-type X(T) operated by a single surgeon, with an average follow-up of 10 years. In this study, basic type X(T) patients who underwent RR (the RR group) showed better results with lower recurrence rates compared with those who underwent BLR (the BLR group). Patients in the BLR group were more likely to relapse within one year compared with those in the RR group (29.3% vs 7.0%, P < 0.001). Although the overcorrection rate was higher in the RR group until four years after surgery, it continuously decreased over time thereafter, and there was no significant difference in both groups beyond the five-year point. Patients with younger age of onset, larger exodeviation at near than at distance, and preoperative hyperopia were related to higher risk of recurrence after surgery.
It is well known that the recurrence rates for surgical intervention in X(T) increases as postoperative follow-up time increases.24 However, most studies reported results within 2–3 years, and only a few studies analyzed long-term observations in X(T). Zibrandtsen et al.25 evaluated the results of 25 patients with 10 years of follow-up, and about 50% of patients had good long-term results. Baker et al.26 evaluated a 20-year follow-up of X(T) surgery in 30 patients, and about 2/3 required only a single surgery. Pineles et al.27 analyzed 50 patients with X(T) who were followed-up for at least 10 years postoperatively and found that 64% of patients showed an excellent motor outcome, including multiple surgeries. In their study, reoperation for recurrent exotropia was done in 48% of patients, which is comparable to our study (39.6% had surgery for recurrence).27 However, these former studies were limited with small number of patients, undistinguished type of exotropia, and lacked a comparison between different surgical methods.
To the best of our knowledge, four prospective randomized studies5,11−13 have compared the surgical outcomes between BLR and RR procedures in patients with X(T). Kushner5 randomized 36 patients with basic-type X(T) into two groups – one receiving RR and the other BLR – and reported that patients who underwent the RR procedure had significantly better surgical outcomes with at least one year of postoperative follow-up. Somer et al11 analyzed 47 patients, and Zhang et al12 evaluated 116 patients, and both reported better surgical success rates in the RR group compared with the BLR group after one year of follow-up. A recent PEDIG study13 reported the results of a multicenter randomized clinical trial in 197 children with 3 years of postoperative follow-up, and did not find a significant difference in the suboptimal surgical outcome by 3 years between X(T) children treated with BLR and those treated with RR. In summary, 3 out of 4 randomized clinical trials support RR in basic-type X(T). In addition, a meta-analysis of papers up to June 2017 indicated that the RR procedure is associated with higher success rates and lower recurrence rates in patients with basic-type X(T). Our study is consistent with the studies mentioned above in that the RR procedure is more effective for basic-type X(T). The strength of our results is based on the large number of patients with a longer follow-up period compared with most of the previously published reports.5,11−13
Meanwhile, considering retrospective studies, Maruo et al.6 reported that BLR produced better outcomes at a 4-year follow-up in 666 patients (66.7% vs 32.8%), but they included other types of X(T) other than the basic-type. Choi et al.9 concluded that the surgical outcome at the 2-year follow up was not different between the two groups in 128 patients; but the outcome after 3.8 years postoperatively demonstrated a higher success rate in the BLR group than in the RR group (58.2% vs 27.4%). However, in their study, the preoperative angle of deviation was larger in the BLR group than in the RR group, which may affect the surgical dose and surgical outcome. Xie et al.29 compared 330 patients for one year and found that there was no statistically significant difference in the success rate between the BLR and RR groups (60.6%vs57.7%), but reported a greater frequency in overcorrection in the RR group. This is similar to our findings in that there was no difference in the initial success rate between the two groups with a higher initial overcorrection in the RR group. However, they compared the results only after 1 year; thus, overcorrection in the RR group may be reduced by exodrift over a long period of observation as in our study.
Burian and colleagues classified exotropia based on distance/near differences.30 They recommended BLR in divergence excessive-type X(T) and RR or bilateral medial rectal resection in convergence insufficiency-type X(T).30 These recommendations are based on the hypothesis that weakening of divergence affects the distance deviation and strengthening of convergence affects the near deviation. Furthermore, Burian30 and Jampolsky31 observed that in patients with basic-type X(T), there is a tendency for secondary convergence insufficiency to develop. This is supported by the studies of Hiles32 and Chia,33 who reported an increase in the near deviation of more than 5 PD in 12–34% of patients with long-term observation. In our study, the risk of recurrence was higher when the near deviation was larger than the distance deviation by more than 5 PD in basic-type exotropia. Thus, this may partially explain why RR resulted in less recurrence compared with BLR after long-term observations.
Studies on the relationship between age of onset and surgical response have shown variable and contradictory results.15,34−36 Several studies have reported that the surgical prognosis of early onset exotropia is poor,34,35 which is similar to our study, showing a worse surgical outcome in patients with an earlier onset. On the other hand, some authors reported that there was no significant difference in the surgical response between early-onset intermittent exotropia and others.15,36 Age at the time of surgery has also been studied as a factor that can affect postoperative alignment.15,37−42 Some reports recommended earlier intervention to get a greater chance of postoperative bifoveal fusion with superior binocular vision and stereoacuity.37–39 However, other studies have advocated a delayed approach, as it may allow more accurate measurements and better results.40,41 On the other hand, several studies showed no difference in the surgical outcomes in children of different age groups.15,42
The relationship between preoperative refractive errors and exotropia have varied among previous studies.41,43,44 Hyperopia43 and myopia44 both have been shown to exacerbate X(T). Conversely, refractive error was not associated with surgical results in another study.41 Generally, hyperopic correction can decrease the demand of accommodative convergence, thus increasing the amount of exodeviation. In addition, children with hyperopia are likely to have poor stereopsis.45 Similarly, in our study, hyperopia greater than + 2.00D preoperatively was a risk factor of recurrence in patients with basic-type X(T).
This study is a retrospective study and has several limitations. First, we only included patients with basic-type X(T), and the results of our study cannot be extrapolated to other types of exotropia. Second, there were more patients in the RR group with fixation preference. This was based on our previous report representing better surgical success rates using RR surgery for exotropia in the dominant eye with fixation preference.8 Third, the surgical dose was not uniform in the BLR group, and 314 of 363 patients had underwent augmented surgery compared with the original surgical table.5,20,28 However, even though most patients in the BLR group had underwent augmented surgery, there were more recurrences after BLR compared with RR. Our result offers an important insight into the high risk of recurrence after BLR recession, regardless of the dosage, and suggests that MR resection may be more effective in the long-term by generating a passive resistance to stretching while in its resting state.
In conclusion, RR was more successful than BLR and likely to minimize the chances of recurrence at an average of 10 years after surgery in patients with basic-type X(T). Patients with a younger age of onset, larger exodeviation at near than at distance, and preoperative hyperopia were related to a higher risk of recurrence after surgery.