They are suspended in a moving gel
Floaters move because they are suspended inside the vitreous, the gel that fills the inside of the eye. When you move your eye, the vitreous moves with it, and the floaters within it are carried along. When your eye stops, the floaters continue to drift for a moment before gradually settling, pulled slowly downwards by gravity.
This is why floaters always seem to lag slightly behind your eye movements, and why they continue to drift across your field of vision even after you have looked in a new direction. It is much like the tea in a cup that continues to swirl after you have lifted the spoon, the movement carries on of its own accord for a little while before finally coming to rest.
They are shadows, not objects
Floaters are not themselves visible objects. They are shadows cast on the retina when they interrupt the path of light entering the eye. Against a pale or bright background, such as a blue sky, a white wall, or a lit screen, there is plenty of light entering the eye, and the shadows cast by floaters are at their most distinct.
Against a dark background, floaters effectively disappear, because there is little light for them to interrupt. This is why people often notice their floaters most when reading or working at a computer, and least when in a dimly lit room.
Your eye moves, and the floater moves with it
This is one of the more frustrating aspects of floaters, and it has a simple explanation. Because floaters are suspended in the vitreous, they move when the eye moves. When you try to look directly at a floater, your eye moves towards it, and the floater is carried in the same direction, always staying just ahead of your line of sight.
You can never quite catch it, because the very movement of your eye is what moves the floater away. The only way to get a floater to stay still is to hold your gaze completely fixed, and even then, it will continue to drift slowly under gravity.
Size and density make a difference
The way a floater moves depends on its size, shape, and position within the vitreous. Small, wispy floaters tend to drift quickly and erratically, carried easily by even minor eye movements. Larger, denser floaters, including the ring-shaped Weiss ring that follows a posterior vitreous detachment, tend to move more slowly and more predictably.
Over time, many floaters drift towards the lower part of the vitreous under gravity, moving away from the central field of vision and becoming less intrusive simply by changing their position.
Gravity settles them overnight
When you sleep, your eyes are still for an extended period and gravity has time to pull floaters to the bottom of the vitreous, away from the central visual axis. When you first wake and look at a bright ceiling or sky, floaters may be absent for a moment before reappearing as the vitreous moves again.
Think of a snow globe left to settle overnight, the snow drifts slowly to the bottom and the scene appears clear. The moment you pick it up and move it, the snow is disturbed and swirls back into view. Floaters behave in much the same way.
Frequently asked questions
Why do floaters move around?
Floaters move because they are suspended in the vitreous gel that fills the eye. When the eye moves, the vitreous moves with it, carrying the floaters along. When the eye stops, the floaters continue to drift for a moment before settling. This is why floaters always seem to lag slightly behind your eye movements.
Why do floaters seem to disappear at night?
Floaters are shadows cast on the retina by structures inside the eye. Against a dark background, there is little light for them to interrupt, so they effectively become invisible. In a bright environment, the contrast between the floater's shadow and the background makes them much more noticeable.
Why can I not look directly at a floater?
Because floaters are suspended in the vitreous gel, they move whenever the eye moves. When you try to look directly at a floater, your eye moves towards it, and the floater moves in exactly the same direction, always staying just ahead of your line of sight.
Why do floaters seem less noticeable when I first wake up?
When you sleep, your eyes are still for an extended period and gravity pulls floaters to the bottom of the vitreous, away from the central field of vision. When you first wake, floaters may be absent for a moment until eye movement disturbs the vitreous and brings them back into view.
Use our interactive Floaters Tool to understand what your symptoms might mean.
Use the Floaters Tool