Horizontal Effects of 10-mm Inferior Oblique Recession versus 14-mm Inferior Oblique Recession

Purpose: The aim of this study was to investigate the quantitative effect of inferior oblique (IO) 10- and 14-mm recession on postoperative horizontal deviation. Methods: Patients (22 men and 18 women) who underwent IO recession were divided into two groups for comparison studies: group 1 (10-mm IO recession, 15 patients) and group 2 (14-mm IO recession, 25 patients). Preoperative and postoperative horizontal deviations were measured, and the resulting horizontal deviations from the 10- and 14-mm IO recession surgeries were compared. The effects of superior oblique underaction, IO overaction, and combined exodeviation on postoperative horizontal deviation were analyzed. Results: Although group 1 did not show a significant horizontal deviation change after surgery ($1.9{\pm}4.5$ prism diopters [PD], p = 0.452), group 2 had a meaningful horizontal change after 14-mm recession ($2.2{\pm}3.8PD$, p = 0.022). Both groups showed a significant esodrift in horizontal deviation (group 1, p = 0.017; group 2, p = 0.030) in patients with exodeviation over 8 PD. The mean change in horizontal deviation was $6.0{\pm}5.4PD$ for group 1 and $9.0{\pm}5.0PD$ for group 2. Although the amount of superior oblique underaction did not affect the extent of change in horizontal deviation, patients with severe IO overaction showed a significant change in horizontal deviation after 14-mm IO recession. Conclusions: Fourteen-millimeter IO recession could make a statistically significant change in horizontal deviation after surgery. In addition, esodrift should be considered after IO recession in patients with a preoperative exodeviation greater than 8 PD or severe IO overaction.