Eumelanin is present in the iris, brain, and hair and comes in a brown and black form. Lipofuscin (yellow in appearance) can accumulate with age and/or ocular disease. Eumelanin is present in the iris pigment epithelium, while both eumelanin and pheomelanin are present in the iris stroma. The main two types of pigment are eumelanin (brown to black pigment) and pheomelanin (red to yellow pigment). The type of pigment affects eye color as well. Variation in the number of melanosomes and the amount of pigment in each melanosome present in the anterior iris stroma determines eye color. A type of cell called a melanocyte produces melanin that is deposited in melanosomes. The melanocytes within the iris stroma and the ciliary body are all derived from neurocrest cells.Īnother important concept is the amount, type, and location of the pigment present. The iris stroma is mainly mesenchymal in origin. The pigment epithelium layer is derived embryologically from the anterior part of the optic cup, and hence neuroectodermal in origin. The posterior layer (the iris pigment epithelium) consists of two layers of cuboidal epithelium. The iris stroma is the anterior layer, consisting of loose collagenous connective tissue, the sphincter and dilator pupillae muscles, blood vessels, nerves, melanocytes, and other cells. The iris is composed of two anatomical layers that both contain pigment. The iris and the ciliary body constitute the anterior uveal coat. It is easier to understand the determinants of iris color with the anatomy of the iris in mind. It can involve the whole iris or only part of the iris (sectoral heterochromia). Heterochromia or heterochromia iridum indicates a difference between the color of the two irises.
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