GFAP and retinitis: While GFAP is known to be expressed in some astrocytes of the healthy nervous system in vivo, like those in the retinal ganglion cell layer (Tao and Zhang, 2014; Luna et al., 2016), Müller glia are thought to express it at very low levels, but upregulate it upon most retinal pathologies, as well known from animal models (Karl et al., 2008; Löffler et al., 2015; Sardar Pasha et al., 2017).