Abnormal development of eyes in mice homozygous for the fidget gene

The eyes of 17‐, 24‐, 28‐, and 31‐somite and 10‐ to 16‐day prenatal, newborn, and 6‐month‐old fidget (fi/fi) mice were studied. The present study showed that the eye abnormalities in fi/fi mice are due to growth retardation of the optic vesicle. In fi/fi embryos the volume of the optic vesicle and its mitotic index were considerably below normal. The reduced growth rate of the optic vesicle led to its delayed contact with the ectoderm and prevented normal lens induction. The lens often did not bud off from the surface ectoderm. In some cases the greatly reduced growth rate of the optic vesicle prevented its contact with the ectoderm and resulted in aphakia. Anophthalmia was also observed, which was caused by the arrest of eye development at the early optic‐vesicle stage. The mitotic index in the wall of myelencephalon and the ventral half of prosencephalon wall was considerably lower than normal. This suggests that the anomalies of the eye and the labyrinth in fi/fi mice are evidently due to an antecedent developmental abnormality of the brain.