To determine the extent of vertical rectus muscle correction in hypertropia showing good prognosis.

A retrospective study was performed with a total of 16 patients who underwent superior or inferior rectus muscle recession surgery with a follow-up of more than 6 months. Vertical muscle recession of 1 mm per 2.5 to 3.0 prism diopters was performed according to the surgeon's discretion.

At 1 week after surgical correction, undercorrection, orthophoria, and overcorrection was observed in 4, 7 and 5 cases, respectively. At the final examination, ocular deviation was decreased in the undercorrected cases and maintained orthophoric except in 1 case where only a small amount of deviation recurred. However, in the cases of postoperative overcorrectionn, ocular deviation increased; 2 cases required surgical correction for consecutive hypertropia.

When performing vertical rectus muscle recession in primary hypertropia, the amount of correction for orthophoria or undercorrection should be determined.