Transverse section of the iris of a pigeon (HE): pigment cells
Birds often have the most brightly colored eyes and in some species, the color varies according to age and sex. Both pigmentary and structural colors contribute to the coloration of the avian iris.
The yellow eye color in chickens is due to the presence of chromatophores called erythrophores that carry carotenoids. In many other birds, pteridine carried by chromatophores called xantophores is the most common pigment. The iris of pigeons can also contain iridophores or guanophores. These cells donâ€™t carry pigments but reflect and refract light using purine (guanidine) platelets (structural color).
Chromatophores and iridophores are present especially in the anterior part of the iris stroma.