Figure 5. Comparison of retina development between the IRBP KO and WT mice at P5. At P5, the transition from a ventricular zone into the distinctive outer nuclear layer (OPL), outer plexiform layer (OPL), and inner nuclear layer (INL) has taken place in the knockout (KO) mice but lagged in the wild-type (WT) mouse. The OPL (indicated by an arrow) is more distinct and continuous in the interphotoreceptor retinoid-binding protein (IRBP) KO mouse (B) than in the WT mouse (A) at P5. The potential implications of a better established OPL are lacking IRBP, the retina develops faster, and IRBP normally slows photoreceptors from connecting to horizontal cells and bipolar cells.