Eye color is determined by genetics and the prescence of a pigment called melanin in the iris. The iris is the portion of the eye which is colored and is surround by the white of the eye (sclera) and the iris has a black hole passing through it (the pupil).
What is the Iris?
The iris is a ring of tissue in the eye which has muscles, connective tissue, and epithelial tissue within it.
It can change the size of the pupil and increase or decrease the amount of light which enters the eye.
The eye color is determined by the presence of the pigment known as melanin in the iris.
Light Eyes (Blue, Green, Hazel)
In people with very light eyes, including blue eyes, green eyes, and light hazel eyes, there is not a lot of melanin in the iris.
Even in these individuals, there is some melanin present, but it is not significant enough to mask the natural color of the iris.
Without much melanin, the iris appears blue and will look more and more brown as melanin is more abundant.
Dark Eyes (Brown, Dark Hazel)
In those people with very dark eyes, the iris has a lot of melanin located in it. This melanin causes the eyes to appear brown or a dark hazel color.
Melanin is a brown pigment and the more melanin that is present, the darker the eyes will appear.
Eyes with No Melanin (Albinism)
Some individuals do not have any melanin in their body. This is the condition called albinism, and is marked by light skin, white hair, and reddish eyes.
In these eyes, the iris can appear red or even violet depending on how the lighting is hitting the eyes.
Determining the Eye Color
To determine the eye color and amount of melanin in the iris, there is a gene that controls the amount of melanin produced in the iris.
Blue eyes and green eyes are considered to be recessive traits which are much less common than brown eyes which are the dominant trait.
It is possible for a person with brown eyes to have a brown eye trait and a blue eye trait, but it is not possible for a person with blue or green eyes to have a brown eye trait.
So when parents are considering what color their children’s eyes may be, there is no definite way to determine the eye color and can only be determined based on probability.
Recessive Eye Color Traits
Blue and green eye colors are recessive traits. These traits are associated with other recessive traits and therefore found together more often than would be expected.
For instance, blue eyes and blonde hair tend to be associated and both are recessive traits.
Similarly green eyes and red hair tend to have an association, and both are recessive traits.
Atypical Eye Colors
There are cases in which the eyes have an atypical color. This can be due to medications that impact the eye color, a lack of vitamins or nutrition, or can be a genetic difference which is otherwise normal.
The eyes may be two different colors even called heterochromia.
Importance of Eye Color
Beyond appearances, the color of the eyes has very little to do with the overall health of the eyes. If the eye color is exceptionally light, the individual may be more light sensitive but it is not guaranteed.
