Eye, orbit, and adnexal structures

Two distinct populations of pigmented cells can be found in the eye. The pigmented epithelial cells of the iris, ciliary body, and retina are derived from the neural tube. These cells undergo reactive hyperplasia in response to a variety of stimuli, but they only rarely undergo malignant transformation. The other population consists of the stromal melanocytes, which can be found in the skin, conjunctiva, and uveal tract. These are neural crest in origin and do not undergo reactive hyperplasia, but they are the source of the most common primary intraocular tumor: uveal melanoma. The uveal melanocytes are considered the counterpart of dermal melanocytes, the source of cutaneous melanoma. (Dermal melanoma is discussed elsewhere in this text. This chapter focuses on eye-related melanomas.)