The eyes alone use 1/3 as much oxygen as the heart, need 10-20 times as much vitamin C as our joints, and require more zinc ( intelligence chemical) than any other organ in the body. Housing 70% of the body' sense receptors, the eyes are the entry point for approximately 90% of all information we learn in a lifetime (with the exception of blind persons).
As a matter of fact, of the 3 billion messages relayed to the brain every second, 2 billion are sent from the eyes. The posterior third of the brain, which houses the memory bank and much of our intelligence, is also the portion of the brain used for vision.
excerpted from Light, Medicine of the Future by Dr. Jacob Liberman