I do not know what causes all floaters but when I had cataracts removed there was debris left in the eye to wash out on its own. Eventually in a couple of months they cleared up. I have had them at various points in life but they neverladt more than a day or so. The floater can look like anything from a shadow to a solid black object. It will usually start at a point after you blink and if you hold the eye still it will settle to the bottom until you blink again. I have been told by several doctors that they are not dangerous but very annoying.