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Iris

The iris is the coloured part of the eye, it forms a pigmented muscular curtain between the cornea and the lens and is pierced by an opening called the pupil. The iris consists of two muscle layers, the sphincter pupillae a circular muscle that when it constricts closes the pupil and the dilator pupillae which when it constricts opens the pupil. The changing pupil size controls the amount of light entering the eye. Eye colour is determined by the amount of pigment present in the iris, a pale blue eye has very little pigmented a dark brown eye is deeply pigmented

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