Whether your eye color is brown or black depends on the amount and type of melanin pigment in your iris. The iris is the colored part of your eye that controls the size of your pupil to regulate light entering your eye. Eye color is determined by genetics and influenced by environment. The possible eye colors range from light blue to dark brown or black. Understanding what makes eyes appear brown versus black can help determine your specific eye color.
Melanin and Eye Color
The pigment melanin is what gives color to your eyes, as well as your hair and skin. Melanin comes in two forms:
- Eumelanin – Brown and black melanin
- Pheomelanin – Red and yellow melanin
Everyone has some amount of both eumelanin and pheomelanin in their body. The predominant type present determines your eye color.
| Eye Color | Melanin Type |
|---|---|
| Blue | Low melanin |
| Green | Moderate melanin |
| Hazel | Moderate melanin |
| Brown | High eumelanin |
| Black | Very high eumelanin |
As you can see, brown and black eyes have the highest levels of eumelanin. The distinction between the two has to do with the concentration and distribution of this melanin in the iris.
What Makes Eyes Brown
For eyes to appear brown, you need to have a high concentration of eumelanin. However, there is variation in shade from light brown to dark brown. Here are some factors that affect the exact brown tone:
- Total amount of melanin – More melanin means darker brown
- Melanin density in the anterior border layer – Higher here means darker brown
- Melanin distribution throughout the stroma – More scattered means lighter brown
- Size of melanin granules – Larger granules appear darker
In light brown eyes, the melanin is concentrated around the outer border of the iris, with less melanin in the central stroma. This allows some light to reflect back and show the lighter brown color.
Dark brown eyes have melanin distributed throughout the anterior and mid-stroma layers. The increased density means less light reflects back, creating the darker shade.
What Makes Eyes Black
For eyes to look truly black, they need to have not only a high total amount of melanin, but also a unique distribution pattern. Black eyes get their color from:
- Very high levels of eumelanin throughout the stroma
- Heavier concentration of melanin at the anterior border layer
- Densely packed granules of melanin
- Nearly total absorption of light by melanin
In black eyes, the melanin is evenly distributed across the anterior border layer and stroma. This uniform denseness allows for minimal light reflectance to give the deep black appearance.
The high concentration of large, tightly packed melanin granules absorbs almost all light entering the iris. This gives the characteristic black color that has a solid, voids-of-color look.
Comparing Brown and Black Eyes
While both brown and black eyes have high levels of the pigment eumelanin, there are subtle differences that set them apart:
| Feature | Brown Eyes | Black Eyes |
|---|---|---|
| Total melanin | High | Very high |
| Melanin density at anterior border | Moderate to high | Very high |
| Melanin distribution in stroma | Moderate density | Very dense throughout |
| Melanin granule size | Mixed sizes | Larger granules |
| Light absorption | High absorption | Maximum absorption |
As you can see, black eyes essentially represent an extreme version of brown eyes, with more melanin overall and a pattern of dense, uniform distribution that allows for minimal light reflectance.
Determining Your Eye Color
If you are unsure whether your eye color skews more brown or black, here are some tips:
- Look at your eye color in natural daylight – artificial lighting can distort color
- Compare to someone with known brown or black eyes
- Look closely to see if your iris has flecks of lighter color – indicates brown
- Note if your eyes look very dark brown or void-like black
- Consider if others call your eyes black or just dark brown
You can also use a high resolution photo of your eye in good lighting. Zoom in and look at the patterns of melanin distribution for clues if your eyes are true black or just very dark brown. If unsure, ask an optometrist to evaluate your eye color during an exam.
Genetics of Brown and Black Eyes
The specific genes that code for melanin production and distribution determine your eye color. Recessive traits for low melanin lead to blue eyes, while brown and black are dominant traits.
| Eye Color | Genes Involved |
|---|---|
| Blue | HERC2, OCA2 |
| Green/Hazel | HERC2, OCA2 |
| Brown | HERC2, OCA2, SLC24A4, TYR, SLC45A2 |
| Black | SLC24A5, HERC2, OCA2 |
If you have ancestors with brown or black eyes, you likely inherited genetic variations of these genes linked to extensive melanin production in the iris. Ethnicity can also give clues, as brown and black eyes are most common in Asian, Hispanic and African populations.
Can Eye Color Change from Brown to Black?
Your eye color is set by the time you are 6 months old and the iris structure is complete. The melanin concentration won’t increase after this age. However, some factors can make brown eyes appear darker over time:
- Melanin granules clump together
- Iris gets thinner and compacts melanin
- Decline in stromal collagen makes iris more translucent
- Buildup of melanin at the anterior border
- Loss of fat and muscle tone around the eyes
These age-related changes reduce reflectance of light, making some brown eyes look increasingly black with advanced age. But the total melanin content stays fixed after infancy so the eye color doesn’t truly become darker.
Conclusion
In summary, brown and black eye color both stem from high levels of the pigment eumelanin in the iris. For eyes to be considered truly black, the melanin content must be very dense and uniformly distributed to allow minimal light reflectance and create the solid black color. Brown eyes have visible difference in shade depending on melanin patterns that permit more light reflectance from the stroma. Examining your iris closely in good lighting and noting your ethnic heritage can help determine if your eye color skews more towards dark brown versus black. While the melanin content is set early in life, changes to the iris structure can make some brown eyes appear blacker with age. But the fundamental genetics of your eye color remain fixed over your lifetime.
