You might not know their official name, but you’ve no doubt seen eye floaters. The perception of these floating apparitions, sometimes also called vitreous floaters or Muscae volitantes (Latin for “flying flies”), is known as myodesopsia. They may appear as spots, small threads, filaments, or cobwebs and they’re not optical illusions. They’re really there, drifting about inside your eyes.

To understand where they come from, it helps to bone up on a little ocular anatomy. At the front of your eye is the cornea, and behind it you can find the pupil (the dark centre of your eye) and the iris (the colourful fringe around the pupil). Between the two lies a small reservoir of liquid called the aqueous humour.

A layer of light-sensitive cells lining the back of your eye is called the retina. When the neurons that form the retina become excited by light, they send messages through the optic nerve and into the brain, relaying information about just what it is you’re seeing. But between the lens and the retina lies an ocean of liquid referred to as vitreous humour, vitreous gel, or sometimes just vitreous.