What is the cause of blindness in preemies?

Too much oxygen: In the old days high doses of pure oxygen were given to prematures to keep them pink. Many ended up blind. Over time it became apparent that it was the fault of the oxygen. The retina is full of tiny blood vessels that go into spasm and may leak blood. Careful monitoring of the retina and treatment has improved outcome. Also, the bright light used for bilirubin can be harmful.