Most of us probably take our eye color for granted. It is an established trait that is part of our identity that we list on our ID. Although it can be changed with contacts now, it is not as easily changed as our hair color. In my case, I grew up thinking that my eyes were blue. As an adult though, a friend became intrigued with my eye color. This friend claimed that my eyes changed color. One day, he said that it was a gray day for them and made me look in the mirror. OK… I finally had to admit that he was correct! How could this be?
As it turned out, I do have what is considered gray eyes. These can appear to be shades of blue or gray. Hazel eye color is another one like this that can appear to change color, but along a spectrum of green, gold, and brown. Eye color can appear to change due to the amount of light present and even the influence on your perception by nearby colors. They are a complex mix of tiny flecks of color that can be seen close up, yet blend into a color shade from a distance. Since that time, I have learned a lot about eye color. I find the science of it makes this trait even more interesting.
Established eye colors
First of all, there are about 8 established colors for eyes: Amber, Blue, Brown, Gray, Green, Hazel, Red, and Violet. Green eyes are rare, but violet also are rare. Many of the genes that establish blue eyes also give green eyes. Numerous children who are born with blue eyes develop the pigment that will establish them as another color as they mature. That eye color is usually established by 3 years of age. This shows us that pigment production can change eye color. The acquisition or loss of collagen deposits will also effect the eye color.
Reflection science involved for eye color
Blue & Green
Blue eyes are not really blue. Our sky looks blue to us because other light is scattered and the blue light is what is reflected back. This is the same effect that is occurring in blue eyes. Most people have brown pigment in the back layer of the iris (pigment epithelium). The front layer (stroma) contains overlapping fibers and cells and even colorless collagen deposits. When there is no pigment in the stroma layer and no excess collagen deposits present, more of the blue light is reflected back and make the eyes look blue. Green eyes have light brown pigment in both layers and yellow pigment in the stroma as well. There is also an absence of excess collagen deposits. A low amount of this pigment mix interacts so that light is reflected back in a way that makes the eyes look green. The addition of collagen deposits in the blue eye structure create gray eyes.
Color Variations & Camera “Red Eye” Effect
Irises can have a variety of colors in their physical mix and that variation in the two layers effect the color seen for the eyes. The pigment combinations, collagen deposits, and the effects of light reflection in the eye combine to create many colors. There are even more rare cases where the eyes are different mix from each other and one eye is a different color from the other (dichromatic or complete heterochromia). The back of the eye can cause the effect for “red eye” when a camera flashes bright light at the eye of a person having their picture taken. Bright light hits too fast for the pupils to react and protect the eye from it. Red reflected back in that flash, is from the color influence of the blood vessels in the back of the eye (retina).
Complete heterochromia (dichromatic eyes) causes a variance between the eyes, that leaves one eye a different color from the other. There are cases where dichromatic eyes are a genetic trait that runs in family lines. Heterochromia can be complete and sectoral or partial. When heterochromia is the result of a change that occurs to the eyes, it is usually because of injury, inflammation, or damage. Central heterochromia is a sectoral heterochromia that is pretty common. This is the case where the inner part of the iris, next to the pupil, is a different color than the outer part. Much less common is a patch within the eye that is a different concentration of color from the rest.
The contributors that give eye color
The roles of genetics and pigments
The genetics of eye color are attributed to many genes and the interactions of these are very complex… so are the combinations of colors that are present in the iris. There are two kinds of pigment present in the iris, lipochrome or pheomelanin (yellow) and melanin (brown). Color that we see for eyes is a combination of the pigments physically present and the light that they reflect out of the eye. There are many, many possible mixtures of pigments and spectrum of eye colors.
The mix that gives the eye color
Amber eyes have a lot of the yellow pigment (lipochrome) present.
Blue eyes have a very low level of pigment present in the iris layers.
Brown eyes are most common and have a lot of melanin (brown) present in both iris layers.
Gray eyes have flecks of gold and brown color seen in the iris eye color mix. As previously mentioned, this is the characteristics for blue eyes with additional collagen.
Green eyes have a very small amount of light brown and yellow pigment. This is one of the rarest colors and is more common in Europe.
Hazel eyes have various shades for the brown and green flecks seen in the iris eye color mix. This eye color has the characteristics for amber or brown eyes with the additional ones for green added into that mix.
Red or Violet eyes have extremely little amount to no pigment present so that blood vessels at the back of the eye influence the color seen in the eye. A red iris has a lack of pigment that is usually attributed to albinism. The combination of blue reflected light from low pigment content along with red from blood vessel influence can result in very rare violet eye color.
The eye colors with little to no pigment (blue, red, violet), all originated from a genetic mutation or inherited genetic mutation.
How the eye color characteristics can show illness/problems
Red iris color means albinism, which usually means that visual acuity is diminished and possible blindness. This can also be a cause for pain and light sensitivity, since there is lack of pigment to block light from entering the eye.
White spots on the center of the eye can be a sign of infection.
Cloudiness of the eye along with light sensitivity can be a symptoms of cataracts which can develop from aging or injury.
Developing a white ring around the outer edge of the iris can be a sign of high cholesterol and triglycerides, which can mean you are at a higher risk of heart attack or stroke.
Redness in the whites of the eyes usually just means irritation from stress or inflammation. The additional factor of pain and other symptoms can mean infection.
White or yellowish bump in the whites of the eye (sclera) near the iris is a pinguecula. These are caused by sun damage and need to be checked because they can be cancerous.
If the whites of your eyes turn yellow, go see the doctor. This is jaundice that can be a sign for a serious problem.
Broken vessels in the eye can look alarming, but are usually from simple causes. Besides eye trauma, this can be caused by an increase in pressure from things like coughing, sneezing, heavy lifting, laughing, crying, or physical exertion. It will take up to 2 weeks to heal.