Both hazel and amber eye colors are considered rare, unique eye colors that stand out from the more common blue, brown, and green eyes. The key differences between hazel and amber eyes have to do with the concentration and distribution of melanin pigments in the iris.
Defining Hazel Eyes
Hazel eyes feature a mix of brown and greenish-gold flecks or streaks around the pupil. The amount of brown and green-gold can vary widely, creating a spectrum of hazel eye shades. While some hazel eyes may appear more brown or greenish-gold overall, the defining characteristic is the presence of both colors in the same iris.
This multi-colored appearance occurs because hazel eyes have moderate amounts of melanin in the anterior border layer of the iris (the front surface) and very little melanin in the stroma (the inner layer under the border). The stroma’s limited melanin allows the reflection of light off the back of the iris, producing the characteristic gold and green colors.
Defining Amber Eyes
Amber eyes are a solid, uniform shade ranging from yellowish to copper-like orange or brownish-orange. Unlike hazel eyes, amber eyes do not display a multi-colored iris. The consistent orange hue is due to a high concentration of lipochrome (a yellow pigment) combined with a low amount of melanin in the iris.
The limited melanin present is mostly distributed throughout the stroma rather than concentrated at the front of the iris, allowing light to reflect off the back surface and produce the rich amber tone.
Prevalence of Hazel vs. Amber Eyes
Both hazel and amber eyes are relatively uncommon. Here is a comparison of the estimated prevalence of each eye color:
| Eye Color | Estimated Prevalence |
|---|---|
| Hazel | 5% |
| Amber | Less than 1% |
As shown in the table, hazel eyes are significantly more common than amber eyes. Approximately 5% of the world’s population has hazel eyes compared to less than 1% with amber eyes. The uncommon nature of both is due to the unique combinations of melanin concentrations required to produce these eye colors.
Geographic Distribution
In addition to the overall rarity, hazel and amber eyes also have distinct geographic patterns:
- Hazel eyes are most prevalent in people of European descent and countries located in Europe. An estimated 10-15% of European populations have hazel eyes.
- Amber eyes are most common in Asia, particularly among East Asians and Southeast Asians. The highest concentrations are found in countries like Thailand, Cambodia, and Laos.
These geographic trends correspond to the genetic and ancestral background influencing melanin production and distribution. The OCA2 gene variant that causes low melanin is significantly more common among East Asian populations, accounting for the higher prevalence of amber eyes in that region.
Causes and Genetics
As mentioned above, both hazel and amber eye colors stem from unique combinations of melanin content and distribution. Here is an overview of the key genetic and biological factors influencing each eye color:
Hazel Eyes
- Moderate total melanin production
- Melanin concentrated at the front of the iris
- Very little melanin in the stroma
- Often associated with Caucasian ancestry and light brown hair/skin
- Associated with genetic variants near the HERC2/OCA2 genes
Amber Eyes
- Low overall melanin content
- Melanin evenly distributed throughout the stroma
- Increased lipochrome pigment production
- Often associated with East Asian ancestry
- Caused by OCA2 gene variant p.Arg419Gln
Genetically, hazel eyes are linked to variants of the HERC2 and OCA2 genes. Amber eyes specifically require the p.Arg419Gln OCA2 variant. These genes regulate melanin production and distribution in the body.
Difference in Melanin and Lipochrome Levels
This table summarizes the key differences in melanin and lipochrome content between hazel and amber eyes:
| Pigment | Hazel Eyes | Amber Eyes |
|---|---|---|
| Melanin | Moderate total amount. Mostly concentrated at the front of the iris. | Low overall amount. Evenly distributed throughout the stroma. |
| Lipochrome | Typical/moderate amounts | Elevated amounts |
As shown, the melanin level and distribution separates hazel from amber eyes. Amber eyes also have more lipochrome compared to hazel and other colors.
Difference in Light Reflection and Absorption
Melanin and lipochrome influence eye color because of how they absorb and reflect light:
- Melanin absorbs blue and green light, producing brown and gold colors.
- Lipochrome absorbs blue light and reflects yellow/red light.
In hazel eyes, the melanin concentration at the front absorbs some light while the low levels in the stroma allow greenish-gold reflection. In amber eyes, the minimal melanin allows light to fully reflect off the back producing a solid amber color.
Appearance Changes with Age
For both hazel and amber eyes, the appearance often shifts with age due to melanin changes:
- Newborn babies with hazel or amber genetics often initially present with blue/grey eyes
- Around 6-12 months the adult eye color develops as melanin levels increase
- Hazel eyes may appear more brown vs. green-gold over time
- Amber eyes may become darker copper/brown
While hazel and amber eyes are considered stable eye colors, natural melanin fluctuations can cause shifts in shade, especially in childhood. However, the eyes maintain their essential multi-colored or solid amber characteristics.
Difference in Rarity
The key factor that makes amber eyes more rare than hazel eyes is the required genetic mutation p.Arg419Gln in the OCA2 gene. Some key points:
- The mutation arose among East Asian populations, so is concentrated in that geographic ancestry
- Hazel eyes can arise from different genetic combinations, so hazel eye prevalence is higher across ethnic groups
- For amber eyes to develop, a person must inherit one copy of the variant from each parent
- The OCA2 variant only occurs in about 5-10% of some Asian populations
Overall, the specific genetic requirements and ethnic distribution of the OCA2 mutation makes amber eyes substantially rarer globally than hazel eyes.
Conclusion
In summary, hazel and amber eyes represent two rare and unique eye colors arising from different concentrations and patterns of melanin. Hazel eyes feature a mix of brown and green/gold caused by moderate total melanin with little melanin in the stroma. Amber eyes have a solid orange/copper color from low overall melanin and increased lipochrome. While both colors are uncommon, amber eyes are significantly rarer due to the required OCA2 gene mutation concentrated in Asian populations. So in the comparison of these two beautiful and exotic eye colors, amber eyes emerge as the rarest type.
