AQP4 and neuromyelitis optica: The aquaporin-4 antibody (AQP4-Ab) is a highly specific biomarker for NMO[5, 6].AQP4-Ab-positive ON has a high risk of eventually advancing into definite NMO, has a common pathogenesis and is classified as NMO spectrum disorders (NMOSD) [7–10].It is unknown whether the structural alterations in AQP4-Ab-positive ON eyes are different from AQP4-Ab-negative ON eyes.OCT is a non-invasive and repeatable technique that can quantify pRNFL and segmented macula layers in vivo[11–14].