Practice question

Following contact with lens placode, distal optic vesicle undergoes invagination to form double-walled optic cup. Signaling from surface ectoderm and lens, including BMP, FGF and Wnt antagonists, patterns cup: inner layer facing lens becomes neural retina expressing Vsx2 and Rx, while outer layer becomes retinal pigment epithelium expressing Mitf and Otx2. The rim contributes to ciliary body and iris. This bilayer originates entirely from neuroectoderm, not surface ectoderm or mesoderm, and later gives rise to photoreceptors, neurons and pigment cells essential for vision and structural support.