Many people with brown eyes find that their eyes can appear to change color and look more hazel or greenish in certain lighting conditions. This is actually quite common and happens due to a optical illusion created by different pigmentation levels in the iris. While eye color is primarily determined by genetics, there are some factors that can affect the appearance of brown eyes.
The Structure and Pigmentation of the Iris
The iris is the colored part of the eye that surrounds the pupil. It contains pigment cells called melanocytes that produce melanin, which gives the iris its color. People with brown eyes have a high concentration of melanin in their irises. However, there is natural variation in melanin content. Some people have more eumelanin which produces brown pigment, while others have more pheomelanin which produces a red-yellow pigment.
The amount and type of melanin present determine the final eye color. Brown eyes get their color from having more eumelanin. But within that brown color there can be different hues and patterns based on the precise pigmentation and distribution of melanin. Some eyes can be a very dark nearly blackish brown, while others are a lighter brown or have a reddish tint.
Why Brown Eyes Can Appear Lighter or Hazel
The interaction between the melanin pigment in the iris and incoming light can affect what color the eyes appear to be. Here are some key reasons brown eyes may look hazel or light brown rather than very dark brown:
– Rayleigh scattering – Shorter wavelengths of light like violet and blue scatter more when they hit the stroma, the fibrous tissue behind the iris. This makes the eyes reflect back less blue and violet light and appear browner.
– Thinner areas of the iris – Some eyes have patches that are thinner with less melanin pigment. Light reflects off the stroma in these areas, making them look lighter.
– Pheomelanin content – More pheomelanin and less eumelanin results in lighter brown or amber eyes. Pheomelanin produces red and yellow hues.
– Lighting conditions – Bright sunlight that reflects off the iris can make brown eyes look lighter. Indoor lighting can also accentuate flecks of lighter pigment.
Differences Between Brown, Hazel, and Amber Eyes
While brown, hazel, and amber eyes may seem similar, there are subtle differences:
| Eye Color | Iris Pigmentation | Appearance |
|---|---|---|
| Brown | High levels of eumelanin | Very dark brown to brownish-black. Little variation or lightening. |
| Hazel | Moderate eumelanin with areas of low melanin concentration | Light golden brown to greenish-brown. More variation in color and lightening. |
| Amber | Higher levels of pheomelanin | Orangey-brown, yellowish-brown, coppery-brown |
Genetic Factors in Eye Color
The amount and type of melanin made is primarily determined by genetics. Here are some key genes involved:
– OCA2 – Plays a major role in melanin production in the iris. Variants determine if eyes are brown, blue, or green.
– SLC24A4 – Affects melanin production and deposition in the iris. Involved in amber/hazel eyes.
– SLC45A2 – Helps regulate processing and distribution of melanin.
– TYR – Controls conversion of tyrosine into melanin. More TYR leads to darker eyes.
However, genetics are not the only factor as environmental conditions can also alter melanocytes and melanin production to some degree. The amount of melanin tends to decrease slightly with age as well.
Can Eye Color Change Permanently from Brown to Hazel?
Eye color is established in infancy and remains relatively stable throughout life. Permanent changes happen gradually and are quite rare. In most cases, brown eyes remain brown. However, some possible ways eye color could shift from dark brown to hazel include:
– Pigment disruption – Trauma, certain medications, and diseases like pigmentary glaucoma can damage the iris and alter melanin content. But significant color change is unlikely.
– Cloudiness – Conditions causing opacity of the cornea or lens like cataracts can make brown eyes appear lighter. Treatment is needed to restore original eye color.
– Lasers or implants – In theory, procedures like laser lightening or colored contacts that alter the appearance of the iris. But these carry risks and may be reversible.
For the vast majority of those with brown eyes, their eye color will remain brown throughout life regardless of changes in lighting or exposure to the sun. Permanent shifts from dark brown to lighter hazel mainly occur due to medical conditions affecting the eyes.
Conclusion
In summary, brown eyes can look hazel or lighter brown rather than very dark brown due to natural variations in melanin pigmentation in the iris as well as different lighting conditions that accentuate those variations. The interaction between melanin concentration and incoming light alters what shade of brown the eyes appear to be. While genetics play a key role in melanin production, some flexibility exists in the evolutionary processes that determine eye color. So brown eyes that appear hazel are actually still brown genetically speaking, just a lighter shade that results from the relative ratios of eumelanin and pheomelanin formed during eye development. Permanent shifts from dark brown to hazel are quite rare later in life. But some conditions affecting melanocytes and deposition of melanin in the iris can lead to gradual changes over time.
