Why do eye-worms occur?

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Eye-worm is not a scientifically correct term. The things I want to pin down are those worm-like shapes, floating in your field of view when unfocused. When you try to focus them, they move away. One explanation, I once heard is, that those are dust-particles floating on the lens. But I am absolutely sure, that this can not be true, due to the fact, that I own one "eye-worm" which has accompanied me for over a year and has stayed in exactly the same shape (a Gaussian-Bell-Curve-Shape with a knot in the middle) for the whole time period. It also moves in exactly the same direction every time when I try to focus on it. If anyone has a clue or theory, why those specs occur, please answer my question.

[edit] Answers

Caveat: I have no medical training.
Floaters are actually in your eye. According to WebMD, you are seeing the thicker, jell-like stuff in your eye. In children, the fluid in the eye is thicker and as you get older, it becomes more liquid, but some of the thicker pieces "float". They are normal and usually go away over time. However, if you notice a sudden or large increase in the floaters, it can be a symptom of a serious problem, like retinal detachment, and it is very important that you contact an eye doctor immediately.