Originally Posted by
cuppajoe_9
If I were to remove your cataracts and not put in an artificial lens, for example, you would be unable to drive a car, but you would be able to keep from being run over by one (an important function of the eye). If I were to remove your iris as well, you would be unable to adjust to how close or far away an object is to you, but you wouldn't be totally blind. If I were to remove all the structures in your eye except for the retina, you would not have functional vision, but you would be able to tell the difference between light and dark, which would be useful if you happened to be a small, cave-dwelling arthropod who eats plants that grow in the light.
On the other hand, if I could, by some very complicated operation, remove only the colour-sensitive cells in your retina, you would still have perfectly functional vision, it's just that the glories of technicolor film would be lost on you.