More details about eye colour

The iris has an equal function for the eyes as a diaphragm has for a camera. There are front and back epithelial layers in an iris. Melanin is present in both layers but its amount changes mostly in front layer. If there is a lot of melanin, then the eyes will be brown. Green eyes have less melanin and blue eyes have the smallest amount of melanin. The most interesting case is that of red eyes. When this occurs, the amount of melanin is extremely low. Because of this light can reflect from the capillaries present in the interior of eyes, and this gives eyes a red colour.
Research has shown that there are many genes affecting eye colour. In recent studies, connection between the colour of the iris and the HERC2 gene was confirmed. This gene is important because of it influence on the OCA2 gene, responsible for coding of protein P. The exact role of protein P is still not understood. It is present in melanin producing cells and it is probably also involved in melanin production. We know of two other genes that influence eye colour. The SLC24A4 and the TYR gene. The TYR gene encodes the enzyme tyrosinase, which is also present in melanin producing cells. Genetic variations in the SLC24A4 gene are connected to skin, hair and eye pigmentation.

Other effects on eye colour

Newborn babies often have blue eyes, which later change to another colour like green and brown. This is due to the fact that exposure to the sun after birth triggers the production of melanin in the iris. The actual eye colour of a child is formed around the age of 6 months. In adults the change in eye colour is rarer, but it can occur if a serious eye injury is present or when taking certain medications in the form of eye drops.

Back to basic description