Abstract
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 (SOPBE) 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 SOPBE and bilateral SOP groups. The degree of subjective excyclotorsion was significantly larger in the bilateral SOP group compared with the unilateral SOPBE 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.
Highlights
Superior oblique palsy (SOP) is the most common paralytic strabismus which causes cyclotorsion [1,2]
Among the 212 patients who were diagnosed with unilateral SOP and showed ipsilateral hypoplasia of the superior oblique muscle (SO) muscle during the study period, 18 (8.5%) patients presented with bilateral fundus excyclotorsion and were classified as the unilateral SOP with bilateral fundus excyclotorsion (SOPBE) group
Two patients from the bilateral SOP group who did not undergo magnetic resonance imaging (MRI) had a clear history of head trauma preceding the onset of signs and symptoms
Summary
Superior oblique palsy (SOP) is the most common paralytic strabismus which causes cyclotorsion [1,2]. When diagnosing SOP, bilateral SOP needs to be distinguished from unilateral SOP, as it is essential to establish the surgical plan [3]. Surgical overcorrection of unilateral SOP can cause consecutive contralateral SOP that exactly mimics masked bilateral SOP [4]. As one of those sensitive signs, is usually regarded as a distinct clinical feature of bilateral SOP to detect masked bilateral SOP in patients with presumed unilateral SOP [5,6]. Muthusamy et al reported the poor sensitivity of the Bielschowsky head-tilt test, the Parks three-step test, and reversal of the hypertropia in distinguishing bilateral SOP from unilateral SOP [5]. Whether bilateral fundus excyclotorsion is a unique feature of bilateral SOP and is not found in unilateral SOP has not been thoroughly investigated
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