Isolated optic nerve involvement in acute lymphoblastic leukaemia: a red flag for early relapse.

Acute lymphoblastic leukaemia (ALL) is the most common childhood cancer, with 70%-80% of cases curable with modern chemotherapy. However, 20% of the cases suffer from disease relapse with bone marrow being the most common site. Isolated ocular involvement as the first sign of relapse is extremely rare, occurring in less than 2.2% of cases. The presentation of optic nerve involvement in leukaemia represents a visual emergency and a sign of isolated central nervous system relapse even in the absence of abnormal cerebrospinal fluid cytology. This case highlights the importance of routine ophthalmic screening in ALL even during maintenance phase and prompt initiation of treatment in cases with isolated optic nerve involvement.