In this study, an ultrastructural analysis of Crx-/- photoreceptors was carried out. As Crx mutations have been associated with Leber's congenital amaurosis, the findings in this study broaden our understanding of the pathology of this disease. Two prominent pathologies were characterized in the Crx-/- retina: (1) An absolute block in outer segment morphogenesis was noted, with the block occuring at the elongation stage of outer segment formation; (2) Crx-/- photoreceptors exhibited a severe perturbation in synapse formation. This represents the first report of a synaptogenesis defect in an animal model of LCA.