Clinical findings, orbital imaging, and intraoperative findings in patients with isolated inferior rectus muscle paresis or underaction.

PURPOSE: To present the clinical findings, orbital imaging, and intraoperative findings of patients with inferior rectus muscle underaction and to determine whether specific findings can help discern the underlying cause.
METHODS: A retrospective observational study was performed on patients presenting with isolated inferior rectus muscle underaction between January 2007 and October 2011. Patient history, ocular motility, fundus torsion, Lancaster red-green plots, and radiographic findings were analyzed. For patients who had surgery, intraoperative findings also were considered.
RESULTS: A total of 28 patients with inferior rectus muscle underaction were identified. Of these, 13 (46%) presented with inferior rectus muscle underaction after orbital trauma; 25 (89%) showed no increase in hypertropia >4(Δ) on head tilt to either side. Fundus intorsion was present in all patients. Of 15 patients evaluated by Lancaster red-green testing, 12 (80%) showed subjective intorsion. Twenty patients underwent orbital imaging via computed tomography or magnetic resonance imaging, and the results in 8 (40%) revealed obvious changes in the inferior rectus muscle. Nineteen patients underwent surgery; intraoperatively, the muscle appeared grossly normal in 8 patients (42%) and showed posterior muscle slippage in 4 (26%). Less common findings included stretched scar formation, flap tear, missing tissue, extensive muscle adhesions, or inability to identify the muscle.
CONCLUSIONS: Clinical findings in patients with inferior rectus muscle underaction are not sufficiently different to identify the cause, and orbital imaging identified a specific abnormality in only 40% of cases.