SPP1 and neurodegenerative disease: Given that OPN is produced and secreted by activated microglia, and acts as a pro-inflammatory mediator in a variety of neurodegenerative diseases (Kim et al., 2004; Schroeter et al., 2006; Choi et al., 2007; Wirths et al., 2010), our findings suggest that OPN plays an important role in inflammation proximal to the primary injury site and is thus useful as a marker of retinal injury.