Eye colour is determined primarily by the brown pigment melanin. Dark eyes have lots of melanin in the iris. Blue eyes only have melanin in a layer on the back surface; this absorbs long wavelengths of light and blue wavelengths get scattered back by the colourless protein fi bres. Albinos don’t even have melanin on the back surface, so the iris is translucent. The red colour is the haemoglobin in the capillaries at the back of the eye. Albino animals find bright light uncomfortable as their irises can’t block as much light as non-albino ones.
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