PAX6 and microphthalmia: The correct dosage of PAX6 is crucial for normal eye development: over-expression of Pax6 in mice results in microphthalmia, retinal dysplasia and defective retinal ganglion cell axon guidance [19], whereas haplo-insufficiency in the mouse results in the phenotype of the small eye (Pax6+/−) or no eye (Pax6-/-) [20].