Hazel eyes, a captivating blend of brown, green, and often flecks of gold, are unique for their multi-toned appearance. While a lasting, fundamental change in the color of an adult’s iris is extremely rare, the dynamic nature of hazel eyes means that temporary, noticeable shifts in hue are very common. These perceived changes are primarily an optical illusion influenced by external factors. However, certain medical conditions or medications can cause permanent alterations.
How Hazel Eyes Get Their Unique Color
Eye color is determined by the amount and distribution of the pigment melanin within the iris stroma. Hazel eyes possess a moderate amount of this pigment, unlike brown eyes (high concentration) or blue eyes (very little). This moderate concentration allows for a distinct interplay between pigment and light. The brown and gold tones come directly from the melanin pigment itself.
The green and blue hues are not caused by separate pigments but by an optical phenomenon called Rayleigh scattering. When light enters the eye, it interacts with the stroma, scattering the shorter, bluer wavelengths back out. This scattered light mixes with the existing pigment to produce the appearance of green or lighter colors.
The unique appearance of hazel is due to an uneven distribution of melanin across the iris. Often, pigment is concentrated heavily around the pupil, creating a brown or gold ring, while the periphery has less melanin. This allows the scattering effect to make the outer edge appear green or blue, making hazel eyes visually dynamic.
Factors Causing Temporary Color Shifts
The most frequent reason hazel eyes appear to shift color is the type and intensity of the light hitting them. Natural sunlight, which is broad-spectrum, tends to highlight the green and gold flecks by maximizing light scattering and pigment reflection. Conversely, artificial indoor lighting, which often has a warmer tone, can cause the eye to appear slightly more brown or amber. The color of clothing or makeup also plays a role, as these colors reflect onto the eye’s surface, enhancing similar tones already present in the iris.
Another significant, temporary factor is the involuntary change in pupil size, known as dilation or constriction. When the pupil dilates in dim light or due to strong emotions, the dark center expands, causing the colors of the iris to compress and appear darker. When the pupil constricts in bright light, more of the iris is visible, making the multi-toned structure more apparent and sometimes lighter.
The autonomic nervous system can also influence the eye’s appearance during strong emotional or physiological states. Intense feelings like excitement, fear, or stress trigger hormonal releases that slightly alter the size of the pupil and affect blood vessels. While the iris pigment remains unchanged, the resulting shift in pupil size and blood flow subtly alters the overall perceived hue.
Permanent Changes and Medical Considerations
While temporary shifts are common, a true, irreversible change in the color of an adult hazel eye is extremely rare and typically indicates a serious physiological event. One known cause of permanent color change is the long-term use of certain glaucoma medications, specifically prostaglandin analogs. These prescribed eye drops stimulate an increase in melanin production in the iris, leading to a gradual and permanent darkening of the eye color.
Sudden, noticeable changes in eye color should prompt an immediate consultation with an eye care specialist, as they can be a symptom of an underlying health condition. Conditions like Fuch’s heterochromic iridocyclitis, a form of chronic inflammation, can cause a loss of pigment, resulting in the affected eye becoming lighter. Pigmentary glaucoma is another condition where pigment granules flake off the back of the iris, which may also cause a change in color.
It is important to note that common myths surrounding permanent eye color change, such as those related to diet or hydration, are not supported by evidence. While hydration can affect the clarity or redness of the white part of the eye (the sclera), it does not alter the inherent melanin structure of the colored iris.