Does the color of the irises affect eyesight (color perception, vision in the dark, etc.)?

To a small degree, Yes. The iris is a muscle sphincter that opens and closes to regulate the amount of light that passes through the pupil into the eye. The iris doesn't actually come in different colors; there is only a single brown pigment (for everybody) that covers its posterior surface. The variations in eye color that we refer to (blue, green, hazel, brown) are more a matter of how thick the iris muscle is. A thick iris is brown and serves to screen out strong light just like a heavy brocade curtain would. A thin iris can be more like a lace curtain -while it does help, there is still a lot of light that can go right through. The apparent colors are due to the scattering of white light differently according to wavelength (like the sky as a matter of fact).

So while visual acuity is not affected by the different colors of the iris, glare and discomfort in strong light can be an issue at times.

_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic