Isolated follicular lymphoma of the inferior oblique muscle presenting as an orbital mass

A healthy, middle-aged woman presented to the ophthalmology outpatient department with a 12-month history of a palpable, non-tender mass on her right lower eyelid. The patient reported a 3-month history of night sweats. Her medical, family and social histories were unremarkable. On examination, her visual acuity was 6/6 in both eyes. She had a mass located inferior to the medial canthus and tethered to the orbital rim. She did not have diplopia, proptosis or strabismus and her ocular examination was otherwise normal. Imaging, biopsy and immunohistochemistry testing confirmed a diagnosis of follicular lymphoma isolated to the inferior oblique muscle. Following diagnosis, she underwent systemic immunomodulatory therapy. Although rare, orbital adnexal lymphoma involving the extraocular muscles should be considered in cases of identified unilateral, painless or localised orbital masses.