Optical Coherence Tomography as an Objective Tool for Assessing Ocular Torsion in Fourth Cranial Nerve Palsy

BACKGROUND: The aims of this prospective study were to evaluate ocular torsion in fourth cranial nerve palsy using optical coherence tomography (OCT), assess the influence of ocular dominance and interocular asymmetry, compare acute and chronic cases with healthy controls, determine diagnostic cutoff values, and analyze associations with clinical parameters and measurement reproducibility. METHODS: In this prospective study, 12 patients with acute palsy, 23 with chronic palsy, and 43 healthy controls were examined. Ocular torsion was quantified by OCT using the disc-fovea angle, and a binocular torsion sum (OCT sum score) was calculated. Clinical parameters included vertical deviation in primary gaze, torticollis, and subjective torsion. Group comparisons and correlations were performed, and reproducibility was assessed in healthy subjects. RESULTS: Greater excyclotorsion in the nonparetic eye was observed in 51.4% of patients and was significantly associated with palsy laterality (P = 0.0016). OCT sum scores were significantly higher in patients than in controls (18.3° vs 10.6°, P < 0.001), with no difference between acute and chronic groups. The OCT sum score showed excellent discrimination between patients with chronic palsy and healthy subjects (area under the curve = 0.927). Correlation with Maddox torsion was moderate, while associations with vertical deviation and torticollis were weak or nonsignificant. Measurement reproducibility in healthy controls was high (intraclass correlation coefficient = 0.86). CONCLUSIONS: Nonparetic-eye excyclotorsion is common in unilateral fourth nerve palsy and is influenced by palsy laterality, likely reflecting ocular dominance. The OCT sum score provides a reproducible, objective measure of binocular torsion and effectively distinguishes patients with chronic palsy from healthy subjects, although its relationship with clinical measures is limited.