Discussion

The estimating incidence of ocular infiltration in ALL varied between 5 and 13%. ^{Reference Taylor, Taylor and Kinsey3} The largest series of 657 children identified a 4·4% rate of infiltration of the optic nerve, retina, iris or orbit. ^{Reference Ridgway, Jaffe and Walton4} Intracranial irradiation and intrathecal chemotherapy are required to prevent recurrence of ALL and to attain the complete remission. The orbital cavity and optic nerve are potential sanctuaries for leukaemic relapse after conventional central nervous system prophylaxis because these structures are shielded during brain irradiation. ^{Reference Taylor, Taylor and Kinsey3} Clinicians should be aware of these possible manifestations even after achieving disease remission. The CNS relapse and ocular involvement in ALL usually indicate refractory disease and a poor prognosis. ^{Reference Surapaneni, Cortes, Thomas, O’Brien, Giles and Koller5} ALL patient have an eye-meningeal risk of relapse and this is more common than in acute myeloid leukaemia and should receive prophylactic treatment of CNS by repeated intrathecal injections of cytotoxic chemotherapy. ^{Reference Kincaid and Green6} Early limited relapse without systemic involvement is a challenge issue for clinical management because the optic nerve is relatively unaffected by systemic chemotherapy and serves as a sanctuary of ALL. ^{Reference Ninane, Taylor and Day7,Reference Brandão, Soares, Salles and Saad8} To confirm the diagnosis of ONI, other causes of decreased visual acuity in ALL have to be excluded like infection, vasculitis, radiation optic neuropathy or side effects of chemotherapeutic agents. ^{Reference Bandyopadhyay, Das, Das and Gayen2} The typical appearance was an infiltration of the entire papillary region by a tumour mass, accompanied by exudates and haemorrhages and forming a projection into the vitreous cavity. Sometimes bilateral, but often asymmetrical, it must be differentiated from papilledema on intracranial pressure. ^{Reference Merle, Richer, Donnio and Jean-Charles9} Decreased visual acuity, perivascular infiltration and parapapillary retinal, an asymmetrical involvement and the absence of clinical signs of intracranial hypertension or meningitis argue for a blast infiltration of the optic nerve. The occurrence of papilledema mechanism is a consecutive venous obstruction to the invasion perivascular by leukaemic cells. ^{Reference Merle, Richer, Donnio and Jean-Charles9} The efficacy of intrathecal chemotherapy is limited because the drug is unlikely to reach the optic nerve located in an optical channel obstructed by tumour infiltration. The most effective treatment is irradiation of the orbit at a dose of 20–24 Gy over 2 weeks. ^{Reference Merle, Richer, Donnio and Jean-Charles9} Early administration of focal radiotherapy allows the cytotoxic drugs to reach the CSF to attack the neoplastic cells. The optic nerve is relatively less sensitive to RT whereas leukaemic cells are quite radiosensitive. It must be done as early as possible to observe a rapid regression and improvement of visual function. Treatment should be instituted before irreversible optic nerve damage occurs. The target volume should involve the posterior poles of the globes with or without whole brain treatment. ^{Reference Kaikov10} Despite intensive treatment, the prognosis is poor and is related to other risk factors of bone marrow with CSF involvement and the length of initial haematological remission. Overall survival in cases where the ocular structures are infiltrated with disease is less than 24 months (9). Two large retrospectives multicentre studies included a total of 59 patients with leukaemic orbital infiltration, most of whom also had bone marrow or CNS involvement. ^{Reference Curto, D’Angelo, Jankovic, Fugardi, Ziino and Casale11,Reference Morris, Buck and Bailey12} Results suggested that patients treated with RT were more likely to achieve remission. The authors recommended doses of greater than 20 Gy to the affected eye. ^{Reference Curto, D’Angelo, Jankovic, Fugardi, Ziino and Casale11} RT to the orbital structures is associated with the risk of long-term morbidity. However, considering that radiation-induced cataracts can be surgically removed, an inadequate RT dose may increase the risk of progression. ^{Reference Taylor, Taylor and Kinsey3} Intravitreal methotrexate administration can be another option therapy in this case relapse. ^{Reference Shenoy, Karam, Udupa and Nayal13}