Some visual disturbances are annoying but nothing to worry about. Others, however, can be signs of a potentially serious condition requiring immediate medical attention. How to tell the difference? Falling into the merely annoying category are eye floaters, which are spots in your vision that drift about when you move your eyes. Mostly caused when tiny strands of your vitreous (the gel-like fluid inside your eye) clump and cast shadows on your retina, they’re usually a natural part of ageing, says the Good Vision Board of Trustees (KGS), an independent German information group. Flickering visi…