Why is it that when you look at something for a long time , when you look at a blank surface the object is still there

Why is it that when you look at something for a long time , when you look at a blank surface the object is still there but in a different colour and blurry? Why do we sometimes get blurry spots on our eyes?

Posted on June 17, 2015 by in Question. Comments Off on Why is it that when you look at something for a long time , when you look at a blank surface the object is still there