Chx10 is a 46kDa homeodomain protein of the paired-like class that is essential for development of the mammalian eye. Mutations in Chx10 cause microphthalmia, a cause of congenital blindness in humans, and the ocular retardation (or) phenotype in mice. In the developing mouse retina Chx10 is expressed in retinal progenitors, while in the mature retina, Chx10 expression becomes restricted to bipolar neurons. Concurrent with these expression patterns, the Chx10-/- (or) retina is thin due to a defect in proliferation of retinal progenitors, and lacks bipolar neurons. Chx10 is also expressed in the developing brainstem, thalamus, and spinal cord.