AQP4 and retinal degeneration: A similar increase in AQP4 labeling of Müller cell processes in the outer nuclear layer was found in rodent models of light-induced retinal degeneration [5], [39] and is likely a response to the outer/subretinal edema which is caused by the opening of the outer blood-retinal barrier that is constituted by the retinal pigment epithelium, and by the volume decrease of cells which undergo apoptosis and which is mediated by extrusion of ions and water from the cells [44]–[46].