Eyes get their color from the iris, this is the tissue that surrounds the eye center which is called the pupil and is itself surrounded by the sclera, the clear tissue making up the surface of the eyeball. The cornea is found in front of the iris with the lens directly behind it.
The Function of the Iris
The principal function of the iris is to control the amount of light passing via the pupil through to the lens and on to the optic nerve at the back of the eyeball. This works in a similar way to the aperture of a camera where the brighter the light the smaller the aperture and vice versa. The iris contains tiny muscles that enable the iris to change, dilating or enlarging the round opening in its center when the light is poor and constricting or reducing it in bright light.
The Color of the Iris
The color of the iris is due to the tiny cells of melanin that it contains. This is the same substance that gives skin and hair their color but in a slightly different cell form. It is the complexity and interaction of the density, texture, pigments and patterns of these cells that make up the color of the iris.
Eye colors vary from shades of brown, green, hazel, grey and blue. Everybody’s iris is as distinct and unique as their fingerprints and there are now security systems that can identify and match each individuals iris to allow or deny access in the same manner as using fingerprints, voice or facial recognition.
The genes of parents determine the color of the iris. That does not necessarily mean that the color will match one or other of the parents, it is a mix of the inherited genes from both parents that will ultimately decide the color.
Most children of European ancestry are born with bluish colored eyes as they have not yet begun to develop the melanin required for determining the color of the eyes. It can take between one to three years for the color to stabilise.
Different Eye Colors
A condition where one eye is a different color to the other, or part of one eye is a different color to the remainder, is known as complete or partial heterochromia iridis and is a result of inheritance or either an injury or disease and is caused by the melanin content of the iris being unevenly distributed.
There is no evidence that eye color has any effect on vision.