Thank you so much for watching my guest video on Tom Scott’s channel! You can see more of my work making science, biology and mathematics videos on my YouTube channel as well as on this blog.

For every video I make, it is my practice to write a blogpost that goes into further detail about everything that didn’t make the video’s final cut, as people generally like to find out more. In today’s blogpost, I’m going to answer the most frequently asked questions about these visual phenomena. I will also be keeping an eye on the comments too and updating accordingly with new questions – so feel free to ask if there is something you would like to know that isn’t already covered here. In my experience, viewers often come up with very insightful questions and perspectives that did not initially occur to me!

Floaters

What Are Floaters Made Of?

Floaters are usually specks of protein, such as filaments of collagen, although occasionally there are also cells, such as photoreceptors, which have come loose from the back of the eye. Collagen filaments however are the most prevalent and they are also much more likely to clump together to form the long cobwebs you’ve probably seen.

Who Gets Floaters?

Most people do actually, but some people are prone to getting more of them than others. Nearsighted people are more likely to have the most floaters due to the fact that the axial length of their eyes (ie – the distance from pupil to retina) is greater than normal or far-sighted people, which means that the content of the eye is more stretched out and at a greater risk of coming loose.

People get more floaters as they get older and the internal properties of their vitreous humour change. With age, it tends to shrink and may pull away from the retina, taking cells with it.

Can We Get Rid Of Floaters?

In practice, not really. Once they are there, they are there to stay. Occasionally, some of the cells may be reabsorbed, and some claim that there are special eye exercises and movements which can help swirl the cells out of your central field of vision.

There are two surgical procedures that can get rid of floaters, but given that possible side effects of both of them are retinal detachment and floaters, I wouldn’t recommend them purely for getting rid of floaters. Both of these procedures in fact are generally used for more serious eye surgery, such as for fixing retinal detachments and tears. Vitrectemy is the draining of the vitreous humour of the eye, and is a good way of replacing the liquid inside the eye and thus removing floaters. The other surgical procedure that is specifically for removing floaters involves targeting the floater with a laser, although, this only works if the floaters are close to the centre of the eye. Typically, the floaters that bother people the most are the ones that can be seen the clearest, and those are generally a fraction of a millimetre in front of the retina and there, are not a good target for lasers. The floaters they can easily target are found closer to the centre of the eye, but those are often quite blurry and interfere less with vision.

Can Floaters Be A Symptom of Anything?

Provided they haven’t appeared suddenly, they are harmless. If they have, and especially if there is a sudden increase in them accompanied by flashes, and perhaps a curtain drifting over your field of vision, this is a sign that your retina is detaching and is a medical emergency. If caught early (within a few hours of experiencing symptoms), it can be easily reversed with routine surgery and somewhat tedious post-surgery care. If too much time is allowed to pass, the retina may detach at the macula point (where detailed central vision is resolved), or even detach completely, and the likelihood of having impaired vision after surgery is much higher.

People who are at high risk of retinal detachment are generally very nearsighted (-6.0 diopters or greater); in their 40-60s (when vitreous detachment generally occurs, the change in the texture of the vitreous humour causes it to shrink and unpeel from the back of the eye, occasionally taking the retina with it); or have received blows or shakes to the head (such as contact sports, car accidents, bungee jumping etc).

Blue Entoptic Phenomenon

The blue entoptic phenomenon is the result of incorrect brain filtering of the shadows cast by the blood vessels onto the retina. This is a topic that I have covered in depth in a previous Draw Curiosity episode, which I shall link down below.

In essence, the red blood cells, which form the majority of the content of the capillaries, absorb light in a different manner to the white blood cells. The brain is able to correct for the shadows cast by the mostly red-blood cell populated blood vessels, but renders the white blood cells as bright white dots. Occasionally, black fringes can be seen too behind the white blood cells, which is the result of a gap that forms between the white blood cell and the following blood flow. Both of these phenomena are illustrated at the end of this video:

Four Ways Our Eyes Are Flawed provides a slightly more detailed overview of the blue entoptic phenomenon as well as two simulations and other flaws in our eye structure which are unrelated to the rest of disturbances talked about today.

I am currently working on part two, Why Our Retinas Are Back to Front, where I will talk about why having this counter-intuitive structure may not be a flaw, but actually provides several beneficial features to our vision, in spite of causing the blind spot and the blue entoptic phenomenon. I am looking to release this video sometime during September and will update this post accordingly when it becomes available.

Visual Snow

What Is It?

Visual snow is the appearance of a static or grainy-like texture over all or parts of the visual field. To a certain degree, everyone experiences it or may experience it under certain conditions. For some people, however, the effect is much more pronounced, to the extent that it becomes pathological and interferes with their vision and wellbeing.

It is most likely a form of photoreceptor noise, in which the photoreceptors are over-sensitive, or triggered as if they had received a signal in the absence of one – which is precisely what happens when you turn up your ISO on your camera.

Our sensory systems involve a complex balance of the signals that are received and a system to decide on whether the signals are ‘true’ signals or not. You could have a very sensitive system that captures more details but also fires in the absence of a signal, or you could have a very insensitive signal that requires much clearer and ‘louder’ inputs before sending on the signals. The case of visual snow is possibly a case of oversensitivity.

Is Visual Snow Pathological?

There are people who report seeing very intense or constant static over all or parts of their visual field, to the extent that it interferes with their quality of life. There is little research into this and whilst some have tried to link it with migraine auras and illicit drug use, evidence points to it being a separate condition all on its own, regardless of whether it is exacerbated by other factors.

Other evidence shows that it is often linked to tinnitus. While multiple factors can cause tinnitus, part of it is a deficit in the brain’s ability to balance the signals being received.

Why Do We Think It Is Neural?

Although there has been little research into the field of visual snow, the studies that have been conducted point to a neural origin for visual snow:

1. People suffering from visual snow that interferes with their quality of life rarely have any abnormalities in eye structure when going for routine eye checks.
2. fMRI scans of people with visual snow show unusual activity in the visual cortex
3. Visual snow fluctuates throughout the day and often gets worse with tiredness.

Phosphenes

Can Phosphenes Be Pathological?

Usually not, but as I mentioned earlier, phosphenes accompanied by an increase in floaters may be a sign of retinal detachment as the photosensitive layer separates from the back of the eye. The flashes are caused by the tugs, and the floaters are cells which have come loose and have been released into the aqueous humour. This is an emergency, so if you experience such symptoms you should call a doctor immediately. When caught early, it can often be treated successfully and with little to no vision loss, but if left to persist, the retina may be harder to reattach and you may end up with permanent vision loss.

Aren’t Phosphenes Caused by ‘Bioluminescence’ in the Eye?

No. There’s a particular branch of pseudoscience that believes that the way we see objects is caused by cells in the eyes emitting light and launching it towards the objects in our surroundings, and that phosphenes are the patterns formed by this emitted light. Whilst this is a neat idea, it is false; none of the cells in our eyes emit endogenous light – unless you’re setting your eyeballs on fire, in which case you probably can’t see anything anyway.

Images are formed by light entering the eye and stimulating photoreceptors that are sensitive to that particular wavelength of light.

Where Can I Find Out More About Vision?

I’ve found vision fascinating for a very long time and I’ve made several entries on this topic – you can read all the associated blog posts here – or watch the full vision playlist here! I’m currently working on 3-4 more vision-related projects, so you can look forward to plenty more in the future!

The video I made for Tom’s channel was based on my personal knowledge of these phenomena and specific details were fact-checked through two of my favourite books on the topic of vision as well as research articles.

If you’re interested in reading and learning more about vision for yourself, these would be my recommendations:

Sönke Johnsen – The Optics of Life 
Richard L. Gregory – Eye and the Brain: The Psychology of Seeing

I hope you enjoyed and learned something new today! Let me know what you think in the comments – I would love to know! If you enjoyed this blog and would like to be notified of new entries, consider signing up to the mailing list here and subscribing to the YouTube channel!