The diversity of eye colors among humans is intriguing, with brown being the most common. Surprisingly, one in four people in the U.S. has blue eyes, while only nine percent are born with green eyes, as reported by the Cleveland Clinic. Beyond aesthetics, eye color can offer insights into vision and ocular health. A recent study on bioRxiv, a platform for preprint studies, suggests that the amount of melanin in the eyes can influence reading aptitude.
Despite the apparent variety in eye colors such as hazel, green, or blue, all human eyes fundamentally possess a brown hue. Gary Heiting, OD, a licensed optometrist and senior editor at All About Vision, explains that eye color is determined by the amount of melanin in the iris, which inherently appears brown. Blue eyes, having the least melanin, reflect and scatter more light than they absorb, while brown eyes, with the most melanin, absorb more light, rendering them darker. The intricate architecture of the iris, combined with melanin levels, plays a pivotal role in shaping eye color.
This architectural complexity extends beyond aesthetics, potentially affecting vision. In a preliminary experiment, Professor Kyoko Yamaguchi and student Faith Erin Cain from Liverpool John Moores University explored the correlation between iris color and reading ability in varying lighting conditions. The study involved 39 adults of European ancestry, including 25 with blue eyes and 14 with brown eyes, encompassing both glasses and contact lens wearers. Participants underwent a 30-second eye test, exposing them to increased luminance while reading codes on a wall in low light.
While individuals with blue eyes may experience heightened sensitivity to sunlight and bright artificial light, they demonstrated a slight advantage in dimly lit situations. Blue-eyed participants showed better readability in darker conditions, with an average minimum of 0.7 lux, compared to brown-eyed counterparts who struggled below 0.82 lux. The study suggests that increased visibility in low light conditions for blue-eyed individuals may result from higher straylight in their eyes, creating a veil of light over the retina.
However, Yamaguchi and Cain acknowledge that more research is needed to fully comprehend the association between melanin content and low-light visual acuity. This exploration into the intricate relationship between eye color and vision unveils potential nuances in how our eyes perceive and respond to varying lighting conditions.
