A newly established mutant strain with mild‐type ocular coloboma (retinochoroidal coloboma without microphthalmia) in albino mice

BACKGROUND: A complicated malformation of the fundus accompanied by typical ocular coloboma was detected in albino fatty liver Shionogi (FLS) mice. We elucidated a new type of 3-dimensional anomalous structure inside the eye in this mouse strain. METHODS: The fundi of FLS mice aged 1, 3, 5, and 20 weeks were observed intensively, both macroscopically and by light microscopy. For the prenatal study, coronal serial sections of eyes of FLS embryos were examined by light microscopy on gestation day (GD) 15.0. RESULTS: The frequency of ocular coloboma was almost 70% in FLS mice, and the inheritance mode of this anomaly is suggested to be autosomal recessive with incomplete penetrance. Stereoscopic observation and light microscopy revealed that the mice had characteristic fundus features at any age during the postnatal period. Following ectopic ciliary epithelia, the surface of the retina protruded like a roof, and on the opposite side of the "roof," a translucent membrane without retinal tissue and choroidal tissue was also consistently detected in the inferior part of the fundus. On GD 15.0, the inner layer and the outer layer were not normally fused at the optic fissure, where a part of the outer layer was absent and the irregular fold of the inner layer was conspicuous in the colobomatous eye of the FLS embryo. CONCLUSIONS: The characteristics of the ocular coloboma in FLS mice are thought to be similar to a mild-type malformation in humans. These ocular defects seem to be situated along the failed fetal optic fissure.