Choroidal Ischemia Sparing the Watershed Zone following Intra-Arterial Chemotherapy for Retinoblastoma.

Intra-arterial chemotherapy (IAC) has become a mainstay in the management of retinoblastoma, especially in advanced or refractory disease. However, IAC is not without complications, and chemotherapy toxic effects can lead to partial or complete choroidal ischemia, often causing vision loss. This is a case report. A 4-month-old girl with bilateral retinoblastoma was treated with secondary IAC (melphalan 5 mg) for recurrent tumor following intravenous chemotherapy. One month later, complete tumor control was achieved. However, she demonstrated broad choroidal ischemia in the nasal and temporal quadrants but sparing of the watershed zone superior and inferior to the optic disc and in the papillomacular region. Fluorescein angiography revealed poor perfusion of the choriocapillaris with visibility of the large choroidal vessels in the nasal and temporal areas but preserved perfusion of the watershed zone. The watershed zone remained intact on the 10-month follow-up, and the final visual acuity was fix and follow without strabismus. The pathophysiology of choroidal ischemia is not well understood, but the fortuitous watershed zone preservation in this case could represent uneven distribution of the chemotherapeutic drug, resulting in partial chemo-dilution of the medication in the watershed region, which represents the final downstream overlapping choroidal perfusion from both medial and lateral posterior ciliary arteries.