Welcome back! This post marks the second installment of our brief foray into the fascinating science of eye color. Today, we will cover green, blue, silver/gray, violet, and red eyes, as well as. I hope you enjoy!
As we’ll discover with blue eyes, the color of green eyes does not result simply from the pigmentation of the iris. The color is caused by the combination of 1) an amber or light brown pigmentation–high levels of the pigment, lipochrome–in the stroma of the iris (which has a low or moderate concentration of melanin) and 2) a blue shade created by the Rayleigh Scattering of reflected light.
Green eyes are among the rarest eye colors, with only 2% of the entire population possessing the specific hue. Most of those individuals
Once again we have an eye color in the category of “light eyes.” Individuals with green eyes may be at an increased risk for eye cancer, specifically intraocular melanoma. People with green eyes can also experience discoloration. Sometimes a yellow pigment known as lipofuscin enters the visible eye color as a result of damaged eyes or wear and tear on the iris. However, this only occurs in green eyes that are unhealthy.
Generally speaking, many consider people possessing green colored eyes to be very desirable and alluring. They are known to have intense, long-lasting relationships. They also bear the stereotype of jealousy and envy, hence the term, “green-eyed monster” or the phrase, “green with envy.”
For those of Irish descent, green eyes contain a connotation of mysticism, mystery, and the magical. Given the historical interaction between the “civilized” world of Rome and the Western world with the “primitive” Celts, green eyes were tied to witchcraft, the dark arts, Druids, and evil. A similar stigma tainted cats. The common eye color between the demon creature and the pagan Celts led nearly all of
The color of blue eyes is structural. This means that the eyes have a very low level of pigmentation in the iris or in the ocular fluid, nor do they have collagen. Instead, the tonality depends on the amount of light dispersed on the eye’s lens, a process known as the Tyndall Effect.
Dissection reveals that the iris pigment epithelium is truly brownish black due to the presence of melanin. Unlike brown eyes, blue eyes have low concentrations of melanin in the stroma, which lies in front of the dark epithelium. Longer wavelengths of light are absorbed by the underlying epithelium, while shorter wavelengths bounce off and undergo Rayleigh Scattering in the turbid medium of the stroma. The same frequency-dependence of scattering accounts for the blue appearance of the sky. The result is a “Tyndall blue” structural color that drastically varies with external lighting conditions.
Tracking the history…
In humans, the inheritance pattern followed by blue eyes parallels that of a recessive trait (in general, eye color inheritance is a polygenic trait, controlled by the interactions of several genes, not just one). In 2008, new research tracked down a single genetic mutation causing blue eyes. A study published in Human Genetics suggests that a mutation in the 86th intron of the HERC2 gene, which supposedly interacts with the OCA2 gene promoter, reduced expression of OCA2 with subsequent reduction in melanin production.
In total, around 8% of the world population, or 600 million people, have blue eyes. Blue eyes are common in northern and eastern Europe, particularly around the Baltic Sea. You will also find individuals with blue eyes in southern Europe, Central, South, and West Asia, and North Africa. In West Asia, a proportion of Israelis are of Ashkenazi origin, among whom the trait is relatively elevated (a study taken in 1911 found that 53.7% of Ukrainian Jews had blue eyes).
Due to the lack of pigmentation, blue eyes can be more susceptible to eye diseases, such as glaucoma, that result from light damage. Since blue eyes have less melanin than darker eyes, they are also more sensitive to the sun and more prone to develop intraocular or uveal melanoma (or melanoma of the eyes). Wearing sunglasses when outdoors may reduce this risk. If you don’t wear sunglasses, you might experience another disease–macular degeneration–due to squinting and straining your eyesight.
Interestingly, and a fact not many know, blue eyes can indicate albinism. Ocular albinism is a rare form of albinism that only affects the eyes. People with this disease often have pale blue eyes. People with this condition often have vision problems. Similarly, bright blue eyes can be a sign of Waardenburg syndrome, a rare genetic condition associated with pigmentation changes and deafness.
On a positive note, individuals with blue eyes are less likely to develop a condition known as vitiligo, which occurs when white patches develop on the skin across the body. These white patches are a result of melanin loss.
According to stereotype, blue-eyed individuals are:
- Most attracted to each other; in general, people believe it is the most attractive eye color
- Deemed trustworthy
- Good and strategic thinkers. Biologically speaking, their brains have slower reaction times due to less melanin in their body, allowing for concentrated thinking and impulse control.
- Might be able to con others easily
- Have great inner and physical strength. Scientific studies reveal that women with lighter eyes tend to handle childbirth better than those with darker colored eyes. They also experienced greater reductions in postpartum depression and anxiety.
Silver eyes have a dark epithelium at the back of the iris and a relatively clear stroma at the front. One possible explanation for the difference in the appearance of silver and blue eyes is that silver eyes have larger deposits of collagen in the stroma. Thus, the reflected light undergoes Mie Scattering (which is not strongly frequency-dependent) rather than Rayleigh Scattering. This would be analogous to the change in the color of the sky, from the blue given by the Rayleigh Scattering of sunlight by small gas molecules when the sky is clear, to the gray caused by Mie Scattering of large water droplets when the sky grows cloudy.
An alternative hypothesis suggests that silver and blue eyes might differ in the concentration of melanin at the front of the stroma. In support of the theory, under magnification, silver eyes exhibit small amounts of yellow and brown color in the iris.
Where might you find silver eyes?
Silver eyes are most common in Northern and Eastern Europe. They are also present among the Algerian Shawia people of the Aurès Mountains in Northwest Africa, in the Middle East, Central Asia, and South Asia.
People born with violet eyes often change eye colors, because, as they grow up, the melanosome cells in the eye mature and produce more melanin.
- Gray is associated with old age, therefore people with this eye color are viewed as gentle and wise
- Because of their calm and gentle nature, people with gray eyes make the best caregivers
- Tend to be very clean and like to keep a clean appearance and house
Violet eyes have a unique history. Known as Alexandria’s Genesis, this eye color results from a supposed genetic mutation. In the reported case of Alexandria’s Genesis, the eyes appear pale silver or light purple (i.e., violet). As the child grows into puberty, the eyes change to a deep purple, which remains throughout adulthood. This change does not affect vision; those with Alexandria’s Genesis are said to have 20/20 vision for their whole life.
While some research has been conducted on Alexandria’s Genesis, the subject remains highly debated. Some scientist claim they can trace the mutation back thousands of years, where it originated in Egypt. Although there is no definitive proof of the mutation going back quite that far, the first recorded case dates to the 1300s.
The other traits associated with the anomaly of violet eyes are questionable at best. These include shimmering white skin impervious to injury or of sustaining a burn or tan; no change in weight once fully-developed; no weight gain but tendency for weight-loss due to a super-charged metabolism. Still other traits hold true. Women with violet eyes experience no menstrual cycles, but remain fertile. These individuals have well-proportioned and developed bodies, as well as strong immune systems with little or no sickness. Children born of a mother with the genetic mutation will be carriers, or might fully develop the mutation themselves.
The final trait and the most debatable is the hypothesis that people with violet eyes do not use their digestive system. Clearly, this trait is not realistic according to human physiology; if it were, the result would be extreme toxicity of the blood and finally, death. Not enough thorough evidence or scientific research exists to support any of the claims; more research remains for scientists to conduct.
Another theory as to the color of violet eyes suggest that they are the product of blue and red tones of pigmentation (the red comes from blood vessels in the eye), as well as a lack of melanin. Violet eyes also signify albinism, which accounts for notions of shimmering white skin unsustaining of tanning. In truth, although the deep blue eyes of some people can appear violet at certain times. G
Violet eyes do not differ from other low or no melanin eye colors when it comes to diseases of the eye. However, due to the inability to handle extremely bright light, retinal detachment is always a concern. You can handle it by simply wearing sunglasses. The lack of UV protectant melanin, the iris is more prone to cancers of the eye and iris. Maintaining regular visits to the optometrist can keep these conditions in check and the eyes healthy.
- Very mysterious
- Noble and refined
- Symbolizes creativity and mystery
- Highly imaginative and spiritual
The eyes of people with severe forms of albinism may appear red under certain lighting conditions owing to the extremely low quantities of melanin. As a result, the light reflects off the blood vessels in the ocular glove, producing the red hue. You can almost look through the iris. Additionally, flash photography can sometimes cause a “red-eye effect.” This occurs when the very bright light from a flash reflects off the retina, which is abundantly vascular, causing the pupil to appear red in the photograph.
Only 0.3% of the population suffers from albinism. These individuals can have eyes of a red, pink, or violet hue. They also generally suffer from photophobia, squinting, myopia, and astigmatism.
We associate nothing specific to red eyes as regards personality traits, most likely due to the sheer rarity of its occurrence in humans.
Heterochromia is a very rare condition in which people have two different colors of eyes. There are two types: essential and acquired heterochromia. The first is caused by having relatively different amounts of melanin in each eye, known as Complete heterochromia; it can also occur in one eye, known as Segmental heterochromia; and occurs because of genetic mutations. The second, acquired heterochromia, results from disease or trauma, such as the contact of the iris with iron, glaucoma, or optic pathology. Heterochromia only affects the eye and doesn’t put the person in mortal danger.
Only 11 in 1,000 people in the
In folklore, the Segmental phenomenon of heterochromia was thought to be indicative of a seer or a piece of your previous identity brought into this life from a former one. The Complete occurrence is often called a “ghost eye.” It’s believed to come with the ability to see spirits or communicate with the other side. Other lore suggests that it’s a sign the eye was swapped out for that of a witch at the child’s birth.
Also known as ‘cat eyes,’ rarer than heterochromia or partial heterochromia, we have central heterochromia. This phenomenon occurs when the diaphragm of an individual contains low levels of melanin, manifesting two distinct colors in the same iris. The result generally arranges itself into an interior and exterior ring around the pupil, with the outer ring being the true color of the person’s eyes. Much like heterochromia at large, central heterochromia might also develop due to ocular damage, genetic chimerism, or mosaicism.
When the Central variety of