Comparative Study On Binocular Fusion And Stereoacuity Of Patients With Intermittent Exotropia Before And After Surgery

[Background] The main treatment of intermittent exotropia is primarily surgical correction at the present, and the main evaluation criteria for surgical treatment of patients with intermittent exotropia are binocular fusion and stereoacuity. Misalignments cause damagements of binocular vision, however, intermittent exotropia is different from other kinds of strabismus, there is fluctuation between orthophoria and exotropia within lday, this can keep opportunities for development of stereopsis. The purpose of surgical treatment is to keep and improve the binocular vision of patients, although surgical aligment is one effective therapy, it always the risk of persistent overcorrection which can produce diplopia, even can cause inhibition of visual cortex, hence, patients lose the function of stereopsis. So, the research of binocular fusion and stereoacuity on patients with intermittent exotropia is always a hot-issue for scholars at home and abroad. Most authors keep agreement that there was significant improvement in binocular fusion and stereoacuity after successful surgical alignment of patients with intermittent exotropia, compared with that before surgery. Yildirim et al took conclusions that patients with X(T) exhibited good near stereoacuity before and after surgery, and that better distance stereoacuity and cen-tral fusion were frequently associated with better surgical success in X(T). However, Holmes et al considered that for children with untreated intermittent exotropia, deterioration in near stereoacuity at1and2years is infrequent, therefore, performing surgery for intermittent exotropia to proactively prevent deterioration of near stereoacuity cannot be justified.[Objective] To compare the binocular fusion and stereoacuity achieved in patients before and after successful surgical alignment of intermittent exotropia. [Method] Retrospective case series study. To examine the binocular function of intermittent exotropia before and after surgery, consecutive cases of114patients of intermittent exotropia with successful surgical alignment (+5～-10PD) in the Eye Center of Provincial Hospital affiliated to Shandong University were retrospectively recruited. To avoid fusional separation caused by covering one eye,prism and alternative cover test and Worth4dots flashlight test, Titmus stereogram was first to evaluate, followed by Worth4dots flashlight test, routine examination and strabismus measurement. Titmus stereogram for the near stereoacuity and Worth4dots flashlight test was used to evaluate the central and peripheral fusion of the patients before and after successful surgical alignment of intermittent exotropia. Prism and alternative cover test was used to evaluate the deviation of the patients fixating at accomdative targets of6m and33cm. Based on the angles examined after surgery,114patients were divided into4groups(Group A:+1～+5PD; Group B:0PD; Group C:-1～-5PD; Group D:-6～10PD). Chi-square test and nonparametric Wilcoxon signed rank test were used to compare the binocular fusion and stereoacuity of patients respectively before and after surgery, P values<0.05were considered statistically significant.[Results] We compared the binocular fusion and stereoacuity of114patients recruited,the resuit was:(1)There were significant difference statistically between binocular fusion evaluated before surgery and that after surgery in patients with intermittent exotropia (P=0.000).Binocular fusion evaluated after surgery was significantly different among4groups (P=0.004).(2) There was statistical significance between stereoacuity examined before and after surgery (P=0.000). Stereoacuity examined before and after surgery was not significantly different in Group A(P=0.336),others had statistical significance(P=0.001).[Conclusions] There was significant improvement in binocular fusion and stereoacuity after successful surgical alignment of patients with intermittent exotropia, compared with that before surgery. With surgical alignment of the eyes of patients with intermittent exotropia, the controlling ability of binocular fusion was improving significantly; the ratio of obtaining central fusion was highest when full correction, secondly, different levels of under-correction, however, the ratio of obtaining central fusion was lowest when over-correction. There was significant improvement in stereoacuity of patients with intermittent exotropia, it included that the ratio of obtaining central fusion was increasing, therefore the stereoacuity was significant improving. There was no significant difference between the stereoacuity of patients before and after surgery in over-correction group(Group A:+1～+5PD), it included that over-correction might bring about unfavorable effect on binocular function. Fusion function and the stereoacuity could improve for most patients with intermittent exotropia; surgical intervention before visual cortical inhibition shoud be practiced, it could help to maintain and improve binocular function.