08-20-2012, 11:03 PM
My understanding is that there is a massive vein that drains blood from the front of the cranium in vitro and that as the fetus developes this vein ceases to do anything. Unfortunately bits of it end up in the eyes and often break off in later life to float around in the eye. I got them in my early 40's and still find them somewhat distracting. Some people get extremely good at ignoring them but I suspect they lose the ability to detect fine movements around them in exchange.