Jason, Canada asked:
Sometimes when I stand up or I exert myself I see little white lights or firework displays in my vision. What is that?
Thatís because when you stand up all of the blood which is circulating round the body suddenly has this big force of gravity pushing it straight down into your legs. The amount of blood coming back up from your legs into you heart to be pumped out into your brain drops. Your retina, the part of the eye that converts light into signals that the brain can understand has the highest metabolic rate of any tissue in the body so if the blood flow to the retina drops very, very slightly for a fraction of a second it starts to fire off abnormal signals. Those are the white lights that you see.