RAX is a paired-type homeodomain transcription factor essential for vertebrate eye development and anterior central nervous system patterning 1. The gene encodes a DNA-binding transcription activator that regulates retinal cell specification and proliferation by binding to photoreceptor-specific regulatory elements 2. RAX expression is conserved across metazoans, with evolutionary evidence suggesting its origin in the common ancestor of Cnidaria and Bilateria, followed by segmental duplication in early jawed vertebrates creating RAX and RAX2 paralogs 3. Beyond ocular development, RAX plays crucial roles in hypothalamic and pituitary patterning, controlling expression of Sonic hedgehog signaling 1. Mutations in RAX cause syndromic microphthalmia 16, characterized by congenital anophthalmia, cleft lip/palate, craniofacial hypoplasia, and endocrine dysfunction including hypopituitarism 4. RAX mutations specifically impair retinal differentiation rather than lens induction, distinguishing its role from other ocular developmental genes 5. Both autosomal recessive and compound heterozygous inheritance patterns have been documented in human patients 2. These findings establish RAX as a critical developmental regulator with broad implications for understanding congenital eye malformations and hypothalamic-pituitary axis development.