Eye floaters—or muscae volitantes, Latin for “hovering flies"—are those tiny, oddly shaped objects that sometimes appear in your vision, most often when you’re looking at the sky on a sunny day. They look like spots, or squishy little amoebae, and drift aimlessly around in your field of vision. Try to get a fix on one, though, and it seems to disappear.
Floaters aren’t just optical illusions. You’re really seeing them, and they’re actually in your eye, not just on it or in front of it. The weird little squiggles are pieces of the vitreous humor, the fluid that fills the eye, breaking off and then floating about in your eyeball.
A little gross, I know, but completely normal. The vitreous humor fills the gap between your retina and lens and helps maintain the round shape of your eye. It’s made up of water bound up in a little hyaluronic acid and collagen. When you’re young, it’s thick and gel-like, but as you age, the hyaluronic acid network breaks down and releases the trapped water molecules. As this happens, the core of the vitreous humor becomes more watery and little bits of undissolved gel break off and slowly drift around. When light passes through the eye, the shadows of these pieces are thrown up on your retina, and you perceive them as floaters.
A Closer Look
Since floaters, well, float, their paths generally follow the motion of the eye. This makes looking right at them difficult. And when you shift your gaze toward them, they often move and stay at the edges. They don’t always float, though; many of them will sink toward the bottom of the eyeball. To get a good look at them, just lie down looking up at a clear sky. Some of the floaters will settle near the fovea, a small area that sits at the center back of your eye and is responsible for your sharp central vision. The lack of movement and the even, texture-less background makes it easy to scope them out and watch the blobs bob around a little.
For the most part, floaters are nothing to worry about—just a sign that you’re not a kid anymore. The sudden appearance of a lot of floaters combined with the onset of other eye weirdness—like flashes of light or blurriness or loss of peripheral vision—could indicate a problem, though. Sometimes, floaters are a symptom of the vitreous humor pulling away from the retina, a retinal tear, or the abnormal growth of blood vessels in the eye. If your floaters cross the line from curiosity to nuisance, it’s time to give your eye doctor a call.
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An earlier version of this story ran in 2012; it has been updated for 2021.