Causes of Floaters

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The back of the eye is filled with a jelly like substance called the vitreous humour. As the vitreous humour gets older, strands of a protein called collagen start to become visible within it. These strands swirl gently when the eye moves. Rather than being solid blobs, floaters are actually shadows cast on the retina by these pieces of collagen. This is because light travels through the vitreous in order to reach the retina, so any objects in the vitreous reflect on the retina.

Floaters are linked to the age of the eye and generally affect people over the age of 40. They are most common in people in their 60s and 70s. This is when the vitreous humour starts to shrink away from the retina, causing it to thicken and clump together, and leading to floaters. This is called posterior vitreous detachment (PVD). The debris left at the site where the vitreous separates from the retina become floaters.

Sometimes, as the vitreous humour pulls on the retina, it cause tiny blood vessels in the retina to burst and bleed into the vitreous slightly. Red blood cells in the blood appear as tiny black dots, or may look like a swarm of gnats, or like smoke. As the blood is re-absorbed, these sort of floaters generally go away, although it can take a few months.

In about half of all people, the vitreous humour has separated from the retina by the age of 50. This normally doesnâ€™t cause any problems and most people arenâ€™t aware that it has happened. In some cases, however, the vitreous remains attached to parts of the retina, and tears the retina as it pulls away. If the retina tears, some blood can escape into the vitreous, causing a â€˜showerâ€™ of lots of floaters at once. You may also see flashes of bright, white light in your vision that look a little like lightening streaks.

These types of flashes arenâ€™t necessarily a sign of retinal detachment â€“ they sometimes happen because of a migraine.

Retinal detachment

Tears in the retina need to be treated straightaway, because they can lead to retinal detachment. This is when the retina separates from the wall at the back of the eye, leading to sight damage. The retina is responsible for changing light into meaningful, electric signals. These are sent through the optic nerve to the brain, where the brain translates the signals into the images we see. If the retina is damaged, the pictures received by the brain become patchy or may be lost completely.

People who are short-sighted, have diabetes, or who have had a cataract operation or an eye injury, are at a higher risk of retinal tears and retinal detachment.

In some cases, floaters can be caused by eye disease or injury that causes inflammation (swelling) inside the eye.