A complicated intraocular malformation accompanied by etinal coloboma and fold formation was detected in an inbred train of albino mice (FLS; fatty liver Shionogi). Defective iris ormation had been frequently observed in some strains of mice ith retinal coloboma in previous papers. The aim of this study s to clarify the morphologic characteristics of iris in this strain. fter the clinical observation of anterior chamber using a penight and surgical microscope (non-invasive method) on both yes of 5-week-old male and female FLS mice, animals were illed, and the eyeballs were fixed by perfusion. After the elimnation of lens, length of the iris was measured, and the anterior hamber and the fundus were observed under the stereoscopic icroscope. Furthermore, histopathological examination was one on the serial sections of the eyes. Downward deviation f the pupil was frequently observed in alive FLS mice by clinial observation. Stereoscopic examination revealed that the iris t the lower region was significantly shorter than that at the ther area, and invagination of the ciliary body and partial retinal oloboma were always accompanied by hypoplasia of the iris. istologically, shortened iris was hypoplastic and associated ith severe or complete loss of pupillary sphincter muscle. All ice with anomaly detected by non-invasive method constantly rovided stereoscopic and histological changes. Conclusion: It is evident that FLS mice show coloboma of he retina and iris with high frequency. These abnormalities were roved to be detectable by a non-invasive method.