[Surgery for acquired trochlear nerve palsy].

BACKGROUND: Various surgical procedures are recommended as treatment for trochlear nerve palsy. Recession of the inferior oblique muscle (IOR), tucking or advancement of the superior oblique tendon, combination of both procedures (COP), and recession of the contralateral inferior rectus muscle are recommended. In this study, the effects of IOR and COP were compared. PATIENTS AND METHODS: Patients with isolated acquired unilateral trochlear nerve palsy were examined at a distance of 2.5 m from the Harms tangent scale before and 3 months after surgery. The onset of the palsy was 1-35 years previously (median 2 years). Subjective squint angles without diagnostic occlusion were measured with a dark red glass in front of the nonparetic eye. The field of binocular fusion was determined with an additional light bar and Bagolini striated glasses for control. The head-tilt phenomenon was defined as the difference between the vertical deviations at 45 degrees of head tilt to the right and to the left. For statistics, squint angles of left-sided palsy were transformed corresponding to palsy on the right side.
RESULTS: The vertical and cyclodeviations were similar before IOR (n=13) and COP (n=21). The reduction of vertical deviation by IOR vs. COP was (median and range) 3 degrees (1; 9) vs. 6 degrees (0; 14) in primary position (PP), in side gaze 5 degrees (1; 11) vs. 9 degrees (3; 17), and in down gaze 3 degrees (-7; 11) vs. 8 degrees (2; 16). Excyclodeviation in down gaze was reduced by 4 degrees (-4; 11) vs. 7 degrees (0; 14), and the head-tilt phenomenon was improved by 1.5 degrees (-5; 7) vs. 6 degrees (-8; 14). Three months after surgery there was residual hyperdeviation of 1 degrees (0; 6) vs. 0 degrees (-7; 5) with excyclodeviation of 2 degrees (-2; 5) vs. 1 degrees (-2; 4) in PP, increasing to 2 degrees (-1; 8), ex 1 degrees (-1; 8) vs. 0 degrees (-8; 5), ex 1 degrees (-2; 5) in contralateral side gaze, and 6 degrees (-3; 13), ex 2 degrees (1; 9) vs. +1 degrees (-1; 8), ex 1 degrees (-4; 10) in down gaze. COP caused more or less significant Brown's syndrome. A second surgery was performed in one patient (4%) after COP. Augmenting surgery was done in four patients (22%) after OIR.
CONCLUSIONS: Cyclovertical deviation and head-tilt phenomenon were significantly reduced when recession of the inferior oblique muscle was combined with tucking of the superior oblique tendon. To permanently minimize squint angles and abnormal head posture, initial postoperative incyclodeviation is necessary, which decreases during subsequent months due to both purely mechanical factors and modulation of cyclovertical innervation. Patient discomfort caused by this may be an argument to perform IOR as an initial procedure with fewer side effects but also fewer effects that may require further treatment.