How Do You Look?

A camera takes high resolution images of visitor’s eyes.

How to Use It

Align your eye with the viewfinder on-screen, then press the button to take a snap!

What Science Tells Us

Several mechanisms are responsible for colour in human eyes. Pigments produce deep browns, orange-browns and yellows. Blue and grey are the result of Tyndall scattering, a type of structural colour. Greens are the combination of yellow-brown pigments and scattered blue light.

Tyndall scattering is a colour-dependant scattering effect. Fine collagen fibres in unpigmented eyes scatter short wavelengths of light more than long wavelengths. In normal white light, this means that blue light is scattered strongly; green light moderately; and red light weakly. We see this combination of colour (lots of blue, some green, not much red) as pale blue/cyan.

Other features that can be seen include fissures and concentric rings, both produced by folding or a ‘concertina’-like effect when the iris dilates. Freckles—areas where dark pheomelanin pigment has been produced, usually as a protective response to ultraviolet light—may also be seen.

Things to Try or Ask

Do family members show similar colouration or structure in their eyes?

What features (freckles, fissures etc.) can you find in your eyes?

Finding the Science in Your World

The Tyndall scattering in blue eyes is similar to the Rayleigh scattering that colours the sky blue. It differs in that the particle size for Rayleigh scattering is much smaller—down to individual molecules—while for Tyndall scattering the structures are about the same size as the wavelength of light.