Attempts at establishing a relationship between the child’s HRQOL and clinical severity of their IXT have proved inconsistent as based on previous literature. A multi-ethnic pediatric eye disease study (MEPEDS)  surveyed children with strabismus at 25 to 72 months of age and found that strabismus reduced the HRQOL in these pre-school children. However, in that study a wide variety of strabismus types were included in their analysis. In the Wang et al’s study, the deviation angle at distance and exotropia control at home were associated with the child’s HRQOL, while Lim et al believed that the child’s HRQOL and clinical severity were not related. Our current results were mixed, that is, the child’s IXTQ was related to near stereoacuity, but not to the deviation angle, NSC and distant stereoacuity. The clinical findings partially correspond with the child’s HRQOL responses. Children’s perception of strabismus differ from that of adults , in part due to the limited attention that children direct to their visual problems . Especially, younger children, who have not yet to form a clear aesthetic concept and an established awareness of their eye disease. Essentially, strabismus is their norm and has little effect on their daily life. Moreover, exotropia in children with IXT appears intermittently, which may also make it difficult for them to consistently respond to this condition and would thus not always affect their quality of life. In contrast, stereoscopic function is more critical for daily events, and, if disturbed may lead to the children’s inability to perform delicate operations[27, 28] and affect their social activities. Patients with IXT experience an initial decline in distance stereoacuity followed by a decline in near stereoacuity. Our findings that children in the later stages of IXT show the affects on their HRQOL may be related to the disturbance of the stereoscopic function.
For parents, their proxy scale scores were also related to near stereoacuity, and the subscale scores of psychological, visual function and surgery opinion had a negative relationship with the deviation angle at near. These results indicate that not only do the later stages of IXT affect the parents’ HRQOL, but also that deviations at near represent their greatest concern. As near deviation can be readily detected by parents, it seems understandable that they would worry that this IXT affects their children’s physical and mental health. These parents would observe the frequency and severity of their children’s near deviation, and therefore be more inclined to take their children to see a doctor as well as being more concerned about the surgical risk and surgical prognosis. Wang et al  found that both the child and their parents’ HRQOL showed a trend toward correlating with clinical severity, with large deviation, poor control and poor stereo function being significantly associated with higher IXTQ scores. In our experience we have found that some patients with a more serious IXT may show a lower HRQOL score, which then predisposes them to ignore the severity of IXT and thereby delay the time for surgery. In fact, the relationship between the angle of deviation, stereoacuity and fusion function are not yet clearly defined , but the larger the angle of deviation the more likely it will be to disrupt the binocular balance. A loss of stereoacuity in children may result in abnormal daily activity that is readily apparent. Overall, the objective clinical findings of IXT do not provide a good representation for the subjective understanding of the disease to these children. The pre-operative HRQOL is related to the later stages of impaired stereoacuity in children with IXT, and may provide a litter bit guide for clinicians to judge the severity of IXT and the time for surgical intervention. However, these HRQOL scores are not in full accord with the severity of IXT. Therefore, it is important for the clinicians to inform parents about all aspects of IXT, including the various clinical features and surgical versus non-surgical interventions, that may help them to make the appropriate decision.
Results of the HADS from parents indicates that they exhibit an obvious tendency for anxiety and depression regarding their children’s IXT. It is clear that the parents are really concerned about their children with IXT, as more than 90% of parents show a decline in mental health. We found that the decline in near stereoacuity can result in a significant amount of anxiety and depression in them, although there is no correlation with other factors such as deviation angle, NSC, and distance stereoacuity. It has been reported that the visual impairment and loss of binocular function are related to symptoms of anxiety and depression. With the decline in binocular function in the later stages of IXT, the resultant abnormal activities in these children may cause anxiety or depression within the parents. Results from a prospective study by Chai et al. reveal that the children, adolescents or adults with strabismus may experience symptoms of anxiety and depression, and that children are more affected and less likely to recover their emotional and mental state. Mcbain  and Snaith  have emphasized that it was society’s and patient’s awareness of the disease that affected the quality of life, not the severity of disease itself. Our results also confirm this. Almost all parents show signs of psychological stress in response to the various degrees of IXT severity in their children, which can explain their anxiety and likelihood to take their children to hospital for treatment.
The post-operative HRQOL in both children and their parents significantly improves, likely due to the changes in the child’s appearance after surgery. In fact, all subscales of IXTQ scores show improvements after surgery. It is generally believed that both the cosmetic and functional recovery of binocular vision following surgery result in a positive impact on the social skills, emotions and mental state of these children. These post-operative HRQOL scores show a significant relationship to the eye position, and even in patients with under- or over-corrections resulting from the strabismus surgery, their post-operative HRQOL scores were substantially improved. Interestingly, these changes in psychological state may not parallel the surgical outcome. For example, Mruthyunjaya et al. noted that subjective satisfaction can be obtained when the eye position is within 10 PD after surgery, even if it is objectively considered as unsuccessful by the surgeon. Archer et al.  also reported that although strabismus surgery in children can improve their HRQOL, there was no statistically significant difference between the successful and unsuccessful surgical outcomes in patients. Another explanation was that as a parent they would evaluate the quality of life of their own child as significant higher after the low risk strabismus surgery regardless of any functional outcome. This is similar to the findings of our study. Strabismus surgery can produce a similar degree of comfort and reduce the patient’s concern about their disease as that in response to a placebo. After surgery, children’s HRQOL scores are consistent with that of their parents. Perhaps, the surgery enables both the children and their parents to attend similarly to the IXT.
There are certain limitations in this study. Currently, no unified criteria exist for the judging of IXT severity. Different methods used for measuring stereoacuity and fusion function may reveal quite different results. In addition, there were a few children in this study with a history of amblyopia treatment and some wore glasses, which may affect their HRQOL. Finally, we did not have a healthy control group, the fact that all patients in our study underwent strabismus surgery, may introduce some bias with regard to the whole population of children with IXT.
In summary, both children’ s and parents’ HRQOL and HADS scores were associated with near stereoacuity. The improvements in HRQOL scores in both the children and parents following surgery indicate that a timely surgery is important for enhancing the quality of life for these children. However, HRQOL scores failed to reflect the seriousness of childhood IXT, nor could these scores be used as an indication for surgical intervention. It is important to note that HRQOL scores vary widely between people as well as in the same illness within an individual over time, as these scores are based on personal assessments and are influenced by physical, psychological and social factors. Nonetheless, these HRQOL scores should be considered by the clinician when evaluating children with IXT to understand the anxiety of these children and their parents and attend to their psychological state.