To characterize the function and mechanisms of cdc42 and sec10 in eye development in zebrafish. Knockdown of zebrafish cdc42 and sec10 was carried out using antisense morpholino injection. The phenotype of morphants was characterized by histology, immunohistology, and transmission electron microscopy (TEM). To investigate a synergistic genetic interaction between cdc42 and sec10, we titrated suboptimal doses of cdc42 and sec10 morpholinos, and coinjected both morpholinos. To study trafficking, a melanosome transport assay was performed using epinephrine. Cdc42 and sec10 knockdown in zebrafish resulted in both abnormal eye development and increased retinal cell death. Cdc42 morphants had a relatively normal retinal structure, aside from the absence of most connecting cilia and outer segments, whereas in sec10 morphants, much of the outer nuclear layer, which is composed of the photoreceptor nuclei, was missing and RPE cell thickness was markedly irregular. Knockdown of cdc42 and sec10 also resulted in an intracellular transport defect affecting retrograde melanosome transport. Furthermore, there was a synergistic genetic interaction between zebrafish cdc42 and sec10, suggesting that cdc42 and sec10 act in the same pathway in retinal development. We propose a model whereby sec10 and cdc42 play a central role in development of the outer segment of the retinal photoreceptor cell by trafficking proteins necessary for ciliogenesis.