2024-03-26 15:49:02
The color of the iris can be used to identify risk factors for certain eye diseases. For whom the risk is increased.
90 percent of all people have brown eyes, the rest are divided into blue, green and gray. The color of a person’s eyes depends on how high the concentration of melanin is in their iris – the pigment that determines not only the color of the eyes but also the color of the skin and hair, according to the German Ophthalmological Society (DOG, Society for Ophthalmology ) explained in a press release.
“The melanin always has the same brownish color – even green and blue eyes have no other pigments,” explains Professor Dr. med. Claus Cursiefen, Director of the Center for Ophthalmology at the University Hospital of Cologne and Secretary General of the DOG. The other color shades were based on light refraction effects that come into play with different melanin contents.
The pigment melanin not only determines the color of the skin and hair, but also protects against the influence of sunlight because it filters both the visible part of the light spectrum and its UV component.
People with light eyes are prone to macular degeneration
People with very light eyes have low melanin levels and are therefore particularly sensitive to strong light. This apparently increases your risk of developing age-related macular degeneration (AMD).
This chronic disease, which usually affects both eyes, is caused by a metabolic disorder. It arises in the macula, the part of the retina that is particularly important for sharp vision, and leads to the gradual loss of vision in this area. You can find out more about it here.
“Free radicals, oxidative stress and the accumulation of waste products in the retina play a role in the development of AMD – processes that are intensified by UV light,” explains Cursiefen. An extensive meta-analysis with almost 130,000 participants was able to prove that at least the wet form of AMD is significantly more common in people of European origin than in people with Asian or African roots.
However, it is still unclear whether this is mainly due to eye color or whether other genetic factors also play a role.
People with light eyes also have an increased risk of developing a so-called uveal melanoma, an aggressive tumor of the choroid.
“Although this type of cancer is very rare, it is found 20 to 30 times more often in people of European descent than in people of Asian or African descent,” explains Professor Dr. med. Nikolaos Bechrakis, President of the DOG and Director of the Essen University Eye Clinic.
Dark-eyed people are more likely to have cataracts
People with dark eyes, on the other hand, are apparently more prone to cataracts, a clouding of the lens. This eye disease develops two to four times more often in people with brown eyes than in blue-eyed people – an effect that has also been demonstrated within the white population and therefore appears to be independent of ethnicity.
“One theory is that the more light is absorbed by the iris, the higher the temperature in the anterior chamber of the eye,” says Cursiefen. With dark irises, a slightly increased temperature exposure can be expected, which in turn represents a known risk factor for the development of cataracts.
The result of surgical procedures on the eye can also depend on the color of the eye. During a corneal transplant, rejection and other complications are more commonly observed when the iris is dark. “It is assumed that melanin has an influence on the immune system in the anterior chamber of the eye,” explains Cursiefen. The pigment may increase inflammatory processes.
“The examples show that seemingly insignificant factors such as eye color could be relevant in everyday clinical practice,” is the conclusion of the DOG experts. It is now important to further define these complex relationships, take them into account in treatment and, wherever possible, compensate for increased risks and disadvantages.