Sir,We greatly appreciate the opinion by Ali et al.[1] on optic nerve infiltration in relapse of acute lymphoblastic leukemia (ALL) in response to our article on unilateral optic nerve infiltration as an initial site of relapse of ALL in remission.The initial presentation of relapse of ALL as isolated unilateral optic nerve infiltration though rare has been reported in the literature.[2-5] After publication of this case report, we found another boy of 10 years in our hospital with similar presentation (unpublished observation). The rarity of this entity may be due to underreporting of the cases.On relapse, the visual acuity of the right eye was 20/200. We agree with Ali et al.[1] that this reduced vision was due to leukemic optic nerve infiltration presenting as unilateral optic disc edema. Following chemotherapy and radiotherapy, there was reduction of optic disc edema. The visual acuity improved only to 20/80, which was less than expected following reduced optic disc edema. The further non-improvement could be attributed to a combination of sequel of optic disc edema and radiation optic neuropathy.The computed tomography scan of brain and orbit showed only right-sided optic nerve infiltration. There was no other sign of central nervous system involvement. The thickened right optic nerve in the computed tomography scan depicts optic nerve infiltration as the cause of optic disc edema excluding true papilledema due to central nervous system involvement. Furthermore, the optic disc edema was unilateral as opposed to true papilledema which is bilateral.To conclude, the relapse of ALL as unilateral optic nerve infiltration may occur in the presence of normal complete blood count and bone marrow examination. Hence, regular ophthalmic check-up is advocated to facilitate early detection of relapse and initiation of combined chemotherapy and radiotherapy.