Growth of vertebrate eyecup is a process that adds ceils in a spatially ordered fashion.Growth of the double-layered eyecup mainly occurs at the edge, where hyperproliferative retina and hypoproliferative retinal pigment epithelium (RPE) make the border structure called cilliary body (CB).Defects in the CB development therefore result in microphthalmia in mammals including human by a molecular mechanism unidentified yet.We found specific enrichment of neurofibromatosis type 2 (Nf2)/Merlin in mouse CB, suggesting potential roles of Nf2 in the development and maintenance of the structure.In a support of the hypothesis and a clinical report on human NF2 patient, the mice lack Nf2 in these areas show defective CB morphogenesis to develop microphthalmic eyes.Our study further provides a mechanistic insight to the roles of Nf2, which controls cell polarity and proliferation of CB, in eye development as well as tumorigenesis.