The subjective controllability of exotropia and its effect on surgical outcomes in patients with intermittent exotropia

In this study, patients with controllability had a later onset of exotropia and a better level of control than patients without controllability. Patients with controllability had better surgical outcomes than patients without controllability. Preoperative ocular exodeviation was a significant factor influencing favorable outcomes in patients with exotropia and controllability.

The subjective symptoms associated with exotropia may differ among patients with intermittent exotropia [5,6,7]. The fusional potential and subjective symptoms of exotropia may be associated. von Nooden observed that the clinical course of exotropia differed depending on the state of the sensorimotor system [5]. For example, a child with large exophoria without any symptoms may develop exotropia in later life or stay exophoric and develop symptoms of eyestrain with sustained close work. We were interested in the controllability of exotropia and evaluated the association between surgical outcomes and controllability.

In this study, 25% of patients reported exotropia controllability. The degree of ocular exodeviation was variable in these patients. Even patients with a large amount of deviation (> 50 PD) showed controllability. A previous study reported that 42% of children expressed a general awareness of exodeviation and various ocular sensations [9]. In their study, some children also demonstrated awareness of their ability to correct the exodeviation by blinking.

The surgical outcomes in patients with controllability were better than those in patients without controllability. Preoperative and immediate postoperative ocular alignment did not differ significantly between patients with and without controllability. Therefore, the differences in surgical outcomes were not due to the immediate effects of surgical treatment. The level of control using LACTOSE control scoring system is better in patients with controllability. The better surgical outcomes in patients with controllability may be due to better binocularity, as patients with controllability may have better binocularity than those without. These results may be consistent with previous study by Moon et al. that higher distance and near LACTOSE scores representing worse control of deviation were associated with higher rates of surgical failure in children with intermittent exotropia [10].

Patients with controllability showed a relatively later onset of exotropia than those without controllability, possibly because patients with better binocularity can maintain normal ocular alignment for a longer time, leading to older mean ages of onset and surgery. Similarly, patients with better binocularity may hide the total amount of ocular exodeviation, leading to variability in ocular exodeviation during follow-up [11,12,13]. Lim and Kim showed a higher possibility of dramatic decreases in ocular alignment before impending surgery caused by anxiety in pediatric patients with controllability [12]. These patients had relatively better level of control [12]. Lee et al. reported better surgical outcomes of exotropia in patients with increased ocular deviation after the monocular occlusion test [13]. They postulated that these patients had a better preoperative fusion rate, which may have concealed the total amount of ocular deviation before the occlusion test. Their better potential fusion capacity may have influenced their response to surgery and facilitated stable surgical outcomes [13].

The decision to agree to surgery in pediatric patients with a large amount of exotropia but good control may be difficult for parents. Parental observations are more likely to correlate with the level of control than with the amount of ocular deviation in pediatric patients with intermittent exotropia [14]. Patients with controllability usually have a good level of control, with variable amounts of ocular deviation. Therefore, parents cannot easily notice ocular deviation and may hesitate to agree to surgery in patients with controllability. Not all patients with exotropia and controllability require surgical treatment [6]. We recommended surgery in patients presenting with any symptoms associated with difficulty on control of exotropia, including asthenopia, diplopia, and headache, or if the trend of these symptoms increases with age. The exotropia gradually progresses with age [15,16,17]. Surgical outcomes are more favorable in patients with controllability than in those without. The results of this study suggest that surgical treatment may be more appropriate in patients with exotropia and controllability.

Our results may help predict prognosis after surgery and may also provide data for the creation of a new classification system for patients with intermittent exotropia. The current general classification system for exotropia is based on the main difference between ocular exodeviation and distant and near fixation or level of control [5, 6]. While these systems are useful in the clinical setting, there may be limitations in predicting the surgical results. Future classification systems that consider not only clinical findings, but also subjective symptoms may be appropriate to better understand exotropia and predict surgical outcomes.

In patients with controllability, a larger preoperative amount of deviation at distance and near was significantly associated with recurrence. These results are consistent with those of previous studies on the prognostic factors of surgical outcomes in patients with intermittent exotropia [2,3,4]. Although patients with controllability had relatively better binocularity, those with a large amount of exotropia were more likely to experience recurrence after surgical treatment.

This study had several limitations. First, we did not evaluate the changes in controllability and subjective awareness of exotropia after surgery. Ha and Kim showed improved subjective symptoms including stereopsis and asthenopia after surgery in patients with constant exotropia [18]. We evaluated only the association between surgical outcomes and the presence of controllability. The changes in controllability and awareness of exotropia require assessment in future studies. Second, this study included only pediatric patients with intermittent exotropia. The clinical characteristics of adult and pediatric patients with intermittent exotropia may differ [19]. Third, the presence of controllability was assessed by directly asking the patient and each patient’s specific accompanying symptoms did not investigate in this study. Further study using questionnaire to evaluate the controllability and accompanying symptoms will be performed.

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