Violet eyes have fascinated people for generations, often appearing in fiction and myth. This uncommon eye color is associated with a few famous individuals, leading many to wonder if it is a naturally occurring human trait. True violet eyes, caused by a distinct purple pigment, do not exist in the human iris. What is perceived as violet is instead an extremely rare optical effect resulting from a unique combination of light scattering and a profound lack of pigmentation. This phenomenon is rooted entirely in the science of how human eye color is determined.
The Mechanism of Human Eye Color
Human eye color is a structural color, determined by the amount of the pigment melanin in the iris and the scattering of light. The color we see is mainly influenced by the front layer of the iris, called the stroma. This stroma contains specialized cells that produce melanin, the brown-black pigment that colors hair and skin.
Brown eyes, the most common color globally, have a high concentration of melanin in the stroma, which absorbs most of the light entering the eye. Blue, green, and gray eyes have very low amounts of melanin in this frontal layer. This low pigment level allows light to interact with the stroma’s collagen fibers, leading to Rayleigh scattering.
Rayleigh scattering causes shorter wavelengths of light, specifically blue and violet, to be reflected back out of the eye, while longer wavelengths are absorbed. This is the same principle that makes the sky appear blue. Eyes that contain little to no melanin in the stroma appear blue, not because a blue pigment is present, but because of the way light scatters. Green and hazel eyes result from a moderate amount of melanin mixing with this blue-scattering effect.
True Violet Versus Apparent Violet
Since the human iris only contains brown-black melanin and yellowish-red pheomelanin, a true violet pigment does not biologically exist. What is described as violet is typically a deep blue or slate-gray eye color that appears violet under certain conditions. This illusion is created when blue light scattering combines with a faint reddish reflection from the blood vessels at the back of the eye, visible through the low-pigment iris.
The eyes of actress Elizabeth Taylor serve as a prime example of this rare optical effect. Her eye color was scientifically recorded as a deep blue, but they often appeared violet in photographs and on film. This appearance was enhanced by professional lighting, specific clothing and makeup choices, and her unique genetic trait of distichiasis, a double row of eyelashes, which framed the dark hue.
Her eyes contained a low amount of melanin that placed them at the edge of the blue-gray spectrum. This allowed slight vascular redness to occasionally mix with the intense blue-light scattering. This confluence of factors creates an indigo or lavender appearance that is visually striking but does not represent a new pigment.
The Connection to Albinism
The one circumstance where eyes may genuinely appear violet or even red is in individuals with albinism. Albinism is a genetic condition caused by mutations in genes like OCA2, resulting in a significant reduction or complete lack of melanin production throughout the body, including the eyes. In severe cases of oculocutaneous albinism, the iris contains virtually no pigment.
Without melanin to absorb light and prevent internal reflection, the iris becomes almost transparent. This lack of pigment allows light entering the eye to pass straight through the stroma, reflecting off the vascular retina at the back of the eye. The hemoglobin in the blood vessels of the retina gives off a reddish or pinkish hue, much like the “red-eye” effect in flash photography.
When this redness from the underlying blood vessels combines with the blue light scattering effect still present in the stroma, the resulting mixture can be perceived as violet. This phenomenon is extremely rare, as most forms of albinism still retain enough pigment for the eyes to appear blue, gray, or light brown. The appearance of violet eyes is an uncommon visual consequence of a genetic condition that prevents normal pigment development.