Melanosis oculi. An ultrastructural study of an affected iris.

The iris of a patient with melanosis oculi was studied, using the transmission electron microscope. An unusual form of macromelanosome was found within the cytoplasm of stromal melanocytes. It is possible that these structures were formed as a result of inappropriate production of the individual subunits of the melanosome. Their presence within stromal melanocytes, but not within the cells of the posterior pigment epithelium, was in keeping with the hypothesis that melanosis oculi is a disorder of melanocytes derived from neural crest.