Hello, I'm an expert in the field of genetics and human biology. Let's dive into the fascinating topic of why some people's eyes change color.

Eyes can change color due to several factors, including genetics, the amount and type of pigments in the iris, the scattering of light by the turbid medium in the stroma of the iris, and even certain medical conditions or drug reactions. Here's a breakdown of these factors:


1. Genetics: The primary determinant of eye color is genetics. Eye color is a polygenic trait, which means it's influenced by multiple genes. The most well-known genes associated with eye color are OCA2 and HERC2, which are involved in the production and distribution of melanin, the pigment that gives color to our eyes, hair, and skin.


2. Pigments: The amount and type of pigments in the iris play a significant role. More melanin typically results in brown eyes, while less melanin can lead to blue or green eyes. The concentration and distribution of melanin determine the final eye color.


3. Light Scattering: The stroma of the iris contains collagen fibers that can scatter light, which can affect the perceived color of the eyes. For example, blue eyes have less melanin, but the scattering of light by the collagen fibers can make them appear blue.


4. Age: As people age, the amount of melanin in their irises can decrease, leading to a lighter eye color.


5. Medical Conditions: Certain medical conditions, such as Horner's syndrome or Fuchs heterochromic iridocyclitis, can cause changes in eye color.


6. Drug Reactions: Some medications can also affect the color of the eyes.

7.
Sun Exposure: Prolonged sun exposure can lead to a decrease in melanin, potentially lightening the eye color over time.

8.
Contact Lenses: While not a natural change, wearing colored contact lenses is a common way people change the appearance of their eye color.

It's important to note that while these factors can influence eye color, the exact mechanisms are complex and not fully understood. The interplay between genetics and environmental factors is still a subject of ongoing research.

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