Clinical features and surgical outcomes of isolated inferior rectus muscle paralysis

Purpose: To describe clinical features of patients with unilateral isolated inferior rectus (IR) muscle paralysis along with type of surgical treatment and results after surgery.

Methods: Patients diagnosed with unilateral isolated IR muscle palsy between 2009 and 2012 that required surgical treatment were included in the study. Diagnosis of IR muscle palsy was done by hypertropia with the largest angle in depression and abduction and inferior rectus muscle underaction.

Results: Twenty-two patients remained in the study; 17 patients (77.3%) had left eye involvement. IR muscle paresis was traumatic in 12 patients (54.5%), congenital in 9 patients (40.9%), and vascular in 1 patient (4.5%). Limitation of duction in the gaze of IR muscle was -2 to -3 in all cases. 3 patients, paradoxically, had contralateral compensatory head tilt (compensatory head tilt to the opposite side of IR muscle palsy). Intraoperatively, we did not detect any gross abnormalities in the IR muscles. The surgical plan at the first operation was IR muscle resection alone in 13 patients (59.1%). At the last follow-up visit, 15 patients (68%) had no deviations in primary position and downgaze. Three cases needed reoperation.

Conclusion: The presence of both ipsilateral and contralateral compensatory head postures in our patients showed that three-step or head-tilt test is not helpful in the diagnosis of IR muscle palsy. In comparison with other studies, more patients in our study were treated with IR muscle resection alone. Also, our reoperation rate was lower than other studies. Absence of gross abnormality in the IR muscles at the operation and partial nature of the paresis may explain these good results. Thus, a considerable number of IR muscle palsy cases with the above characteristics may be treated successfully by one muscle surgery (IR muscle resection).