Contributor: Gordon K. Klintworth
Hypoplasia of  the iris stroma or the iris pigment epithelium is not uncommon. Segmental areas of poorly developed iris stroma permit the underlying sphincter pupillae and iris pigment epithelium to be seen easily. This hypoplastic iris may represent a developmental anomaly that almost became an iris coloboma [coloboma - iris] but in which the iris has just succeeded in closing. Iris hypoplasia  may be accompanied by changes in Descemet membrane and even congenital hereditary endothelial dystrophy. This defect  must occur after the fourth month of intrauterine life, but its pathogenesis remains uncertain. One possibility is that a persistent embryonic blood vessel prevents full development of the adjacent stroma. In some cases the iris hypoplasia may follow atrophy after normal development. Disorders associated with iris hypoplasia include Down syndrome and Neuhauser syndrome.