Marketing Scoops: color

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Five people have been able to perceive a colour never before seen by human eyes, after researchers used lasers and tracking technology to selectively activate certain cells in their retinas. The blue-greenish hue has an intensity, or ‘saturation’, outside the natural range of colours seen by humans. The work is “amazing technically” and an “extraordinary achievement”, says Kimberly Jameson, a colour-vision scientist at the University of California, Irvine………Continue reading…..

By: Elizabeth Gibney

Source: Nature

Critics:

Eye color is an inherited trait determined by multiple genes. These genes are sought by studying small changes in the genes themselves and in neighboring genes, called single-nucleotide polymorphisms or SNPs. The total number of genes that contribute to eye color is unknown, but there are a few likely candidates. A study in Rotterdam (2009) found that it was possible to predict eye color with more than 90% accuracy for brown and blue using just six SNPs.

In humans, eye color is a highly sexually dimorphic trait. Several studies have shown that men are more likely to have blue eyes than women, while women are more likely to have darker eye colors (green and brown eyes) than men. Sex is therefore a major factor in the expression of eye color genotypes. One study suggested that women’s higher levels of the sex hormone estrogen may explain why women tend to have darker eyes than men.

People of European descent show the greatest variety in eye color of any population worldwide. Recent advances in ancient DNA technology have revealed some of the history of eye color in Europe. Through the analysis of ancient DNA, a 2020 study published in Experimental Dermatology suggested that the common gene for blue eye color likely originated in the Near East and arrived in Europe around 42,000 years ago, after the exodus out of Africa.

A 1997 study of White Americans found that eye color may be subject to change in infancy, and from adolescence to adulthood. Seventeen percent of children experienced a change of eye color by adulthood. Of those children, 50% of developed lighter eyes as they got older. The other 50% developed darker eyes. Generally, children with hazel and light brown eyes tended to experience a lightening of their eye color by adulthood. Children with green eyes often experienced a darkening of their eye color.

It was also found that 11% of the children’s mothers experienced an eye color change during the same period, with most developing lighter eyes, relative to their original color at the time of their child’s birth. The most important role of melanin in the iris is to protect the eyes from the sun’s harmful rays. People with lighter eye colors, such as blue or green, have lessened protection from the sun, and so need greater protection from the sun’s rays than those with darker eye colors.

Those with lighter iris color have been found to have a higher prevalence of age-related macular degeneration (ARMD) than those with darker iris color; lighter eye color is also associated with an increased risk of ARMD progression. A gray iris may indicate the presence of a uveitis, and an increased risk of uveal melanoma has been found in those with blue, green or gray eyes.

However, a study in 2000 suggests that people with dark brown eyes are at increased risk of developing cataracts and therefore should protect their eyes from direct exposure to sunlight. Eye color outside of the iris may also be symptomatic of disease. Yellowing of the sclera (the “whites of the eyes”) is associated with jaundice, and may be symptomatic of liver diseases such as cirrhosis or hepatitis.

A blue coloration of the sclera may also be symptomatic of disease. Although people with lighter eye color are generally more sensitive to light because they have less pigment in the iris to protect them from sunlight, there is little to no evidence that eye color has a direct impact on vision qualities such as visual acuity. However, there is a study that found that dark-eyed people perform better at “reactive-type tasks”, which suggests they may have better reaction times.

People with light-colored eyes, however, performed better at so-called “self-paced tasks”, which include activities like hitting a golf ball or throwing baseballs. In another study, people with darker eyes performed better at hitting racquetballs. There are also other studies that challenge these findings, and more study is needed to verify these results.