Organogenesis of mild ocular coloboma in FLS mice: Failure of basement membrane disintegration at optic fissure margins

► The optic cup does not fuse at midlenticular level in FLS fetuses by GD 15.5. ► Rolling on one side of fissure margins and consequent asymmetry are observed. ► The basement membrane persists after contact of both sides of the fissure margins. ► The basal lamina is not disintegrated and mesenchymal cells intervene. ► Disturbed basement membrane disintegration causes mild ocular coloboma in FLS mice.