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

PurposeTo 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.MethodsA 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.ResultsA 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 >4Δ 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.ConclusionsClinical 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.