Bilateral Fundus Excyclotorsion in Unilateral Superior Oblique Palsy Confirmed by MR Imaging

Purpose: To determine whether bilateral fundus excyclotorsion is helpful in distinguishing bilateral superior oblique palsy (SOP) from unilateral SOP by investigating bilateral fundus excyclotorsion in unilateral SOP and comparing the features with bilateral SOP using fundus photographs. Methods: This retrospective cohort study included a total of 212 subjects who were diagnosed with unilateral SOP with hypoplasia of a single superior oblique (SO) muscle and 7 subjects with clinically diagnosed bilateral SOP. Fundus excyclotorsion measured by modified fovea–disc angles and inter-eye differences in cyclotorsion angles (the difference in fundus excyclotorsion angles: paretic eye or hypertropic eye in primary gaze–fellow eye), and subjective cyclotorsion were compared between groups of unilateral SOP with bilateral fundus excyclotorsion (SOP_BE) and bilateral SOP. Results: Bilateral fundus excyclotorsion was found in 18 out of 212 patients (8.5%) in the unilateral SOP group, and 7 out of 7 patients (100%) in the bilateral SOP group. Among the 25 patients with bilateral fundus excyclotorsion, the mean angle of excyclotorsion (5.7° ± 4.7° vs. 7.6° ± 4.3°, p = 0.125) and the inter-eye differences (0.7° ± 3.6° vs. 0.5° ± 5.8°, p = 0.615) were not significantly different between the unilateral SOP_BE and bilateral SOP groups. The degree of subjective excyclotorsion was significantly larger in the bilateral SOP group compared with the unilateral SOP_BE group (16.0 ± 5.5 vs. 4.6 ± 4.3, p = 0.002). Conclusion: Bilateral fundus excyclotorsion was demonstrated not only in bilateral SOP, but also in unilateral SOP at a rate of 8.5%. Bilateral fundus excyclotorsion alone did not prove to be a specific sign in distinguishing bilateral SOP from unilateral SOP.