Hemi-naevus of Ota: perturbation of neural crest differentiation as a likely mechanism.

We present a case of oculodermal melanosis that involves the lower eyelid and lower half of the globe in a very clearly defined fashion. We suggest that such a lesion is the result of a local change in embryonic environment occurring during a well-defined stage of ocular development, such that differentiation of neural crest cells into a melanocytic phenotype is favoured.