When we look into someone's eyes, we're typically thinking of their iris. This thin disc of pigmented tissue gives us our eye color. You would think that scientists would know every detail of such a commonplace structure, but work by geneticist Jeremy Nathans shows that there is still much to discover.

Nathans and his research team set out to genetically 'map' each cell type in the iris and discovered something surprising - four new types of cells. The new cell types are shown on the map here: two new types of structural cells called stroma shown on the right-hand side and bottom; and two types of muscle cells, sphincter 1 and sphincter 2, that retract in response to light.

These discoveries offers clues for how to develop new diagnostic tests and treatments for diseases that affect the iris and provides new information about how the iris forms during early development.

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