Using conventional surgical procedures, such as myectomy or recession of inferior oblique muscle, higher postoperative vertical overcorrection due to contralateral concealed IOOA were observed in mild primary position hypertropia with unilateral IOOA.~To achieve better outcome, IOBT was introduced. Yang et al. firstly reported that IOBT might be a useful alternative surgical treatment for patients with primary position hypertropia of less than 5△ that was associated with IOOA. Recently, our study has reported that IOBT achieved satisfactory outcomes in patients with mild primary position vertical deviation (≤10△) with unilateral IOOA, without any risk of overcorrection of vertical deviation and contralateral IOOA. Although our results are promising, there is no enough evidence to recommend IOBT for primary position hypertropia with inferior oblique overaction. A large randomized trial is needed to compare the surgical successful rate and suboptimal surgical outcomes of IOBT with IO-Rec for primary position hypertropia with inferior oblique overaction.~The proposed trial will be conducted in 9 different study sites working in the field of pediatric ophthalmology and strabismus. Each site will have one certified surgeon to do all surgeries. For IOBT, the whole belly of inferior oblique muscle is secured with a 6-0 absorbable suture, and then anchors to the sclera 5 mm behind the temporal insertion of the inferior rectus muscle. For IO-Rec, the insertion of inferior oblique muscle is excised and secured with a 6-0 absorbable suture, and then anchors to the sclera 4 mm behind and 2 mm beside the temporal insertion of the inferior rectus muscle.
This is a multi-center, randomized double-blind controlled trial to compare the effectiveness of IOBT with IO-Rec for the treatment of hypertropia with IOOA.~Specific Aim 1 (Primary): To study the suboptimal surgical rates between IOBT and IO-Rec for the treatment of hypertropia with IOOA.~Specific Aim 2 (Secondary): To compare the surgical successful rate of IOBT with IO-Rec for the treatment of hypertropia with IOOA.