An 83-year-old woman presented with a 10-day history of sudden-onset diplopia in the left eye, with no preceding trauma or anticoagulant use. Initial orbital magnetic resonance imaging (MRI) on day 10 revealed a well-circumscribed retrobulbar lesion along the left inferior rectus muscle. The lesion showed heterogeneous T1 hyperintensity, low-to-intermediate T2 signal, and no definite solid enhancement, raising concern for a hemorrhagic orbital mass or neoplasm. Serial noncontrast computed tomography (CT) on days 20 and 49 showed progressive decreases in lesion size and attenuation. Follow-up MRI on day 180 confirmed complete spontaneous resolution, with no residual abnormality or underlying neoplasm. This case demonstrates that serial CT and MRI can guide safe conservative management of spontaneous retrobulbar hematoma and help avoid unnecessary surgery in clinically stable patients.