Definition of CMZ regions for the analysis of regionalized gene expression. Schematic drawing of histological landmarks that define four areas in the CMZ: peripheral, middle, central-inner and central-outer (shaded regions). The outer plexiform layer (OPL) divides central-inner from central-outer. The definitive ganglion cell layer (GCL) derives from the middle CMZ, reflecting their early birth order. Progenitors in central-inner CMZ are destined for the inner nuclear layer (INL) and the central-outer region produces cone photoreceptors in the outer nuclear layer (ONL). Arrows, blood vessels; RPE, retinal pigmented epithelium; OLM, outer limiting membrane; IPL, inner plexiform layer; M, Müller glial cell.