Without oxygen consciousness is lost in 5 seconds and permanent damage occurs within 4 minutes. If it is cut, one side of the brain cannot communicate with the other. If one side is damaged, the other side can take over its functions, but it must be retaught. Strokes are more common in men over 65 with high blood pressure. They occur throughout the retina, except in the fovea just behind the lens.
All vertebrates have rods.