What are eye floaters?

Discover what causes these optical oddities

(Image credit: Marina Vitale)

Gazing up at clear blue skies can sometimes be interrupted by what appear to be bouncing squiggles of dust that evade our attempts to focus on them. These mysterious floaters are not specks on the surface of our eyes, but rather a part of the eye itself.

Filling the gap between the lens and retina is a pool of jelly-like fluid called the vitreous humour. As we age this eye jelly naturally begins to degrade and very slowly liquify. During this lifelong process, tiny ‘clumps’ break away and surf in the surrounding jelly. Known as vitreous floaters, they are most common in older people and those who are short-sighted.

Often unnoticed in day-to-day life, these floaters usually make an appearance when we stare at a bright, blank canvas, such as a blue sky. As light enters the eye, these vitreous floaters obscure the light and cast a shadow over the light-detecting cells at the back of the eyes – the retina. When this communicates with the brain via the optic nerve, tiny lines of light are missing, so we see the floaters as shadows.

This biological shadow-puppet show is no cause for alarm in those that witness it. However, should the group of squiggles and wiggles increase dramatically then a trip to the optician may be necessary. This could potentially be a sign of retinal detachment, where the thin cellular lining tears and peels away from supporting blood cells, which can cause permanent sight damage.

How does the image of vitreous floaters form in our minds eye?

1. Incoming light

As light enters the eye and is focussed on by the lens, the obscuring floater casts a shadow over the retina, blocking the light.

2. Retina receival

At the back of the eye, a thin layer of cells called the retina receives light and converts the information into electrical signals, which are delivered to the brain for interpretation. (Image cretit: Scientific Animations)

3. Vitreous floaters

Over time, clumps of the protective fluid form within the vitreous humour. This is a jelly-like area responsible for keeping the eyes' shape. The clumps float around within the eye.

4. Disturbed vision

By preventing light from reaching the retina, a silhouette of each floater is formed in our vision


This article was originally published in How It Works issue 129, written by Scott Dutfield 


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