Differences in the corrective effects of vertical transposition accompanied by recession–resection of the horizontal rectus muscles for complicated vertical deviation

Background/objectives To investigate whether the corrective effect differs between upward and downward transpositions or between exotropia and esotropia in vertical transposition accompanied by horizontal rectus muscle recession–resection. Subjects/methods This prospective study investigated 41 patients with concomitant exotropia or esotropia with small-angle vertical deviation who underwent unilateral vertical transposition accompanied by horizontal rectus muscle recession–resection and were followed up for 1 year postoperatively. We analysed the vertical deviation corrective effect, defined as the corrective amount per displacement distance (°/tendon width [TW]). We compared the corrective effects between upward and downward transpositions and between exotropia and esotropia. Additionally, we investigated the correlation between the corrective effect and the studied parameters. Results The 1-year vertical corrective effect was 5.2 ± 4.6° (9.0 ± 8.1 prism dioptres [Δ])/TW. The 1-year vertical corrective effect of upward transposition (7.9 ± 4.0° [13.8 ± 7.0Δ]/TW) was higher than that of the downward transposition (3.9 ± 4.4° [6.8 ± 7.7Δ]/TW, P = 0.009). In contrast, upward and downward transposition did not differ between exotropia and esotropia ( P = 0.62). Multivariate analyses revealed that the 1-year vertical corrective effect correlated with the vertical transposition direction (upward or downward) and preoperative vertical deviation but did not correlate with the disease type (exotropia or esotropia). The 1-year motor success (vertical deviation ≤ 5Δ) rate was 89%. Conclusion The vertical corrective effect of vertical transposition accompanied by horizontal rectus muscle recession–resection is greater in upward transposition than in downward transposition; however, it does not differ between exotropia and esotropia.