The role of animal models in our developing understanding of anterior segment dysgenesis is outlined. Research in avian models shows the importance of the neural crest in the development of the anterior segment and the failure of terms such as anterior segment cleavage adequately to describe the embryology of this area. Study of the anatomical differences between the anterior segment of the primate and that of the sub-primate mammal explains the differences seen in the dysplastic changes occurring in the iridocorneal angle in man and those occurring in sub-primate mammals such as the rabbit or the dog. Such work gives an improved understanding of congenital lesions seen ophthalmologically in man as well as those encountered in veterinary ophthalmology.