I sometimes see small things floating in my field of vision. What are they and should I be worried?

Those are called floaters. They are small particles that accumulate in the vitreous, the jelly-like substance that fills the eye, and cast a shadow on the retina. Most of the time, floaters are harmless. If, however, you see several new floaters, or floaters accompanied by flashes of light, you should contact your eye health care provider.