We’ll start with the important stuff: they’re not hallucinations, they’re not aliens, and you’re probably not suffering from some horrible disease. We’ll talk about a few of those things later – excepting aliens – but odds are you’re just experiencing some extremely normal visual phenomena known as phosphenes.
Phosphenes can come in an almost limitless array of random forms. However, for the most part, they’re complex, shifting lightfields which someone will see after they close their eyes.
You may also be dealing with simple afterimages, which occur when cells in the eye perceive light for long enough that they continue to send signals to the brain even after you move to a darker area or close your eyes. However, these aren’t particularly likely unless you’ve been recently staring at a light source. Nope, you’re probably seeing phosphenes.
But how exactly are the two different? And what really causes phosphenes in the first place?
A Phosphene Primer
An extremely common explanation for phosphenes is that they’re caused by the “background noise” made by our eyes when they’re at rest.
Even if you’re not consciously using them, your eyes remain active. Not incredibly active by any stretch, but they’re still burning energy and firing off the odd electrical impulse. Put all of that together and it’s enough to stimulate visual cells and produce the odd, hazy patterns that characterize phosphenes.
There’s another common brand of phosphene worth talking about though, and those are pressure phosphenes. Notice how using your hands to press or massage your eyelids can produce some minor eyelid fireworks – these are, again, phosphenes, just a different kind.
Like regular their calmer cousins, pressure phosphenes take on an extraordinarily diverse range of appearances. They’ve been variously described as patches of blue light, rings, auras, and simple light or dark patches.
These occur thanks to mechanical force acting as a stimulant on eye cells, activating them and producing phosphenes. This generally comes in the form of eye rubbing, but has a few other potential causes.
Ever heard of someone “seeing stars” after a sharp blow to the head? Cliched, but not inaccurate – sudden physical force can easily produce a new batch of phosphenes. Sneezes and other violent, quick movements can also rattle your eyes into producing some bright spots.
You’ll also find some much more uncommon varieties of phosphenes. For example, they’ve been noted in patients exposed to high magnetic forces. Electrical phosphenes deserve a special mention. These blobby patches of light may resemble other phosphenes, but they happen completely differently. They’re actually born in research labs, where scientists have produced them by electrically stimulating patients’ brains.
As to why they’re using them, we’re talking about nothing less than artificial sight. Many blind individuals are capable of perceiving phosphenes in response to electrical stimulation. By controlling where and when they appear, physicians can actually use them to represent real-world objects perceived by an attached camera. In short, they can give patients a basic facsimile of normal sight. One of the first people to do this was famed biomedical researcher William Dobelle, whose early experiments with the process would give rise to the first commercial brain-computer interfaces – devices that gave patients some sight back, although only in a limited and often temporary fashion.
Still, phosphenes aren’t the only kinds of visual phenomena that can crop up uninvited.
What About the Squiggles You See When Your Eyes Are Open?
Again, you’re probably not in trouble – just about everyone sees these small, wormy intruders from time to time.
Commonly called “floaters“, these specks are bits of solid detritus that form in the normally clear fluid that makes up the vast majority of your eye. Once they show up, they’ll occasionally drift across your field of vision, obstructing light as they do and allowing you to perceive them.
For most, this isn’t much more than a fleeting curiosity or annoyance. In some cases, however, it’s a sign of something worse. Any sudden increase in the number of floaters you see should be enough to send you running to an eye doctor. This population boom could be the result of a retinal tear or similar injury, any of which can potentially cause lasting damage to your eyesight.
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Other Types of Visual Phenomena
Getting back to closed eyes, there are a few more potential causes of your current visions. Closed-eye hallucinations are relatively common, and do broadly include phosphenes, but also incorporate a couple of other interesting causes.
The first is “the prisoner’s cinema”. Stay in the literal dark for too long, and you’ll find yourself experiencing closed-eye hallucinations of varying complexity. While this phenomenon is well-documented, scientific explanations are a little thin. It’s possible that an extended lack of stimulation tricks the visual system into trying to make sense out of existing low-level noise that might normally produce simple resting phosphenes.
A similar scenario may come from a disease well-known for the hallucinations it produces: Charles Bonnet Syndrome, or CBS. CBS sufferers are generally older, have severely impaired vision, and suffer intense, recurring hallucinations. This appears to happen when the visual system, deprived of the information it generally relies on to make sense of a person’s surroundings, begins to conjure up its own data, overcompensating to the point of conjuring up vivid, unreal imagery.
On a less medical side, some meditation practitioners also report seeing closed-eye hallucinations. Again, this may come from keeping one’s eyes closed for long periods of time, but it’s not something desperately in need of scientific explanation.
For most of us, these lightfields are just a sign that our eyes have a normal level of activity. While they can be a sign of more serious problems, phosphenes are almost always benign or even helpful. So, feel free to settle back, close your eyes, and enjoy your personal light show worry free.