Levels of Hedgehog activity bias optic progenitor cell fates. In wild-type, Hh activity forms a proximal-high, distal-low gradient within the optic vesicle. This leads to normal specification of the OS, RPE, and NR. In Ift172 mutants, Hh activity is moderately elevated within the optic vesicle, which results in the expansion of the OS into the proximal optic cup as well as the expansion of RPE into the inner optic cup. In Ift122 mutants, Hh activity is strongly elevated throughout the entire optic vesicle, which results in optic progenitors adopting an optic stalk-like identity.