Bilateral optic neuropathy secondary to chronic lymphocytic leukaemia infiltration

A man in his late 50s with recently diagnosed chronic lymphocytic leukaemia (CLL) developed rapidly progressive bilateral, painless vision loss. Despite significant visual impairment, initial fundus examination, optical coherence tomography and neuroimaging were largely unremarkable. Further investigation revealed visual field defects, optic nerve dysfunction on visual evoked potentials and cerebrospinal fluid (CSF) infiltration by leukaemic cells, confirming bilateral leukaemic optic neuropathy (LON). The patient was treated with high-dose intravenous methylprednisolone followed by ibrutinib, resulting in marked visual recovery and normalisation of visual fields. Temporary discontinuation of ibrutinib due to neutropenia led to symptom recurrence and persistent central nervous system infiltration, which improved after treatment was resumed. This case highlights the diagnostic challenges of LON, particularly when ophthalmic and imaging findings are initially normal, and underscores the importance of CSF analysis and prompt CLL-directed therapy to prevent irreversible visual loss and achieve favourable outcomes.