Researchers find a clue to a glaring problem.
U2's Bono, TV presenter Magenta Devine and a whole host of supermodels and actors are rarely to be pictured day or night without their sunglasses.
But now scientists in America and the Netherlands believe some people may not don dark glasses out of choice, but because of their genes.
Researchers at the Massachusetts Eye and Ear Infirmary and the University of Groningen have discovered a genetic defect which could explain why some people have difficulty adjusting to bright lights.
Their work, published in Nature, identified genetic flaws in five unrelated individuals which impair the eye's ability to quickly adjust to changes in light.
In the past, defects in the activation of photoreceptor cells have been found, but this is the first time scientists have discovered why people have problems in recovering after exposure to light.
One of the researchers, Dr Aart Kooijman, said in the Netherlands, some patients were identified with abnormal recovery from the influence of strong light flashes - some found it difficult to play ball games because they could not see a moving ball.
And going from inside to outside on a sunny day, they would be essentially blind for five to 10 seconds.
The team found the incurable condition seemed to be helped by wearing dark glasses.
BONO: The U2 star is often seen in dark glasses