Is his eye damaged? I was under the (mistaken?) impression that he had one blue eye and one brown.
One of his eyes was damaged and the lens does not dilate at all in response to light. IIRC, he got injured as a child.
This is from Wikipedia. It generally agrees with the stories I read at least 20 years ago:
When Bowie was age fifteen, his friend George Underwood, wearing a ring on his finger, punched him in the left eye during a fight over a girl. Bowie was forced to stay out of school for eight months so that doctors could conduct operations in attempts to repair his potentially-blinded eye.[8][9] Underwood and Bowie remained good friends; Underwood went on to do artwork for Bowie’s earlier albums.[10] Doctors could not fully repair the damage, leaving his pupil permanently dilated. As a result of the injury, Bowie has faulty depth perception. Bowie has stated that although he can see with his injured eye, his colour vision was mostly lost and a brownish tone is constantly present. The colour of the irises is still the same blue, but since the pupil of the injured eye is wide open, the colour of that eye is commonly mistaken to be different.[9]