Abstract
The aim of this study was to investigate whether the limbus-insertion distance (LID) of the lateral rectus (LR) muscle can be a useful indicator for predicting the surgical effect of recession surgery in intermittent exotropia (IXT). Patients who underwent unilateral or bilateral LR recession for the basic type of IXT were included. The distance between the corneal limbus and the posterior edge of the insertion of LR muscle (limbus-insertion distance) was measured intraoperatively using surgical calipers (graded with 0.25 mm precision). We calculated the actual dose-response effect as the difference between the angle of preoperative deviation and the angle of postoperative deviation, and then divided the figure by the total amount of recession at postoperative months 1, 3, and 6. The correlation between the limbus-insertion distance (LID) of LR muscle and each dose-response effect was statistically analyzed. A total of 60 subjects were enrolled in this study. The mean LID of LR muscle was 5.8±0.7 mm. The dose-response effect was 3.2±1.0 prism diopters (PD)/mm at postoperative month 1, 3.4±1.0 PD/mm at postoperative month 3, and 3.4±1.1 PD/mm at postoperative month 6. The LID of the LR muscle was significantly correlated with dose-response effects in cases of unilateral and bilateral LR recession at postoperative months 3 and 6 (P = 0.01, <0.01, 0.04 and <0.01 respectively). As the LID of the LR muscle increased by 1 mm, the dose-response effect increased by 0.2PD/mm in unilateral LR recession, and by 0.4 PD/mm in bilateral LR recession at postoperative month 6. In conclusion, the LID of the LR muscle can be used as one predictor of the recession effect to assist in surgical planning for IXT. Moreover, undercorrection at the time of LR recession might be considered in patients with long LID of the LR muscle.
Highlights
Intermittent exotropia (IXT) is one of the most common types of childhood strabismus in Asia [1]
All patients were diagnosed with comitant intermittent exotropia
As the limbus-insertion distance (LID) of the lateral rectus (LR) muscle increased by 1 mm, the dose-response effect increased by 0.2 prism diopters (PD)/mm in unilateral LR recession, and by 0.4 PD/mm in bilateral LR recession at postoperative month 6
Summary
Intermittent exotropia (IXT) is one of the most common types of childhood strabismus in Asia [1]. It was previously accepted that an initial overcorrection for IXT may result in a better surgical outcome [5]; it is challenging to predict postoperative outcomes after recession surgery. Knowledge of the factors affecting postoperative outcome in IXT is important for surgical planning and patient counseling. One of the previous studies demonstrated that a large preoperative deviation and a large initial overcorrection are significantly associated with postoperative exodrift [6]. This finding suggested that these two parameters are useful predictive factors of postoperative outcomes in IXT. Another study suggested that the tendon width could have an effect on the outcome of recession surgery in IXT [7]
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