Structural Eye Color is Amazing

The stroma is a delicate interlacement of fibres. Some circle the circumference of the iris and the majority radiate toward the pupil. Blood vessels and nerves intersperse this mesh. Wikipedia

Brown

In brown eyes, the stroma contains a high concentration of melanin, which absorbs most light and creates a dark brown hue. In the illustrations below, “collagen” refers to excess collagen deposits in the stroma.

Hazel

In hazel eyes, the stroma contains a moderate amount of melanin, giving a light brown hue with occasional sections of green and yellow. Because of the moderate amount of melanin, a good portion of light is scattered back into the atmosphere by the stroma.

Green

In green eyes, the stroma contains a small amount of melanin which provides a light brown hue that mixes with… well, what exactly does that brown light mix with to create green light?

Blue

In blue eyes, there is no melanin present in the stroma. The stroma is essentially colorless until light enters and is then scattered and reflected back into space. This is why the color of blue and green eyes depends on the quality and quantity of light available in a room. This phenomenon of material appearing to have a certain color while no pigmentation of that color is present is called structural coloration, and it’s awesome. It occurs in beef, berries, butterflies, and more.

Grey

Grey eyes are a curious case, and extremely rare. Grey eyes are similar to blue in that they contain no melanin, but they do contain excess collagen deposits in the stroma that interfere with Tyndall scattering, blocking the appearance of blue hues. (That’s the current theory anyway).

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Reduce suffering | Teach humans about being human | Donate money