What's Really Happening When We See 'Stars' After Rubbing Our Eyes?

Photo illustration by Mental Floss. Images: iStock.
Photo illustration by Mental Floss. Images: iStock.

It's likely happened to you before: You start rubbing your eyes and almost immediately begin seeing colors, specks, and swirls from behind your closed lids. So what's happening when you see these 2001-esque "stars"? Do they only occur upon rubbing? Does everyone experience them?

Before we can get to what causes the lights, we need to understand a bit about how the eyes work. Angie Wen, a cornea surgeon at New York Eye and Ear Infirmary of Mount Sinai, tells Mental Floss that the retina—the innermost layer of the eye—consists of millions of cells, or photoreceptors. These cells, she says, "are responsible for receiving information from the outside world and converting them to electrical impulses that are transmitted to the brain by the optic nerve. Then, the brain interprets them as images representing the world around us."

However, what we see doesn't just stop there. Sometimes "we see light that actually comes from inside our eyes or from electric stimulation of the brain rather than from the outside world," Wen says. "These bursts of seemingly random intense and colorful lights are called phosphenes, and appear due to electrical discharges from the cells inside our eyes that are a normal part of cellular function."

People have been writing and theorizing about phosphenes for thousands of years. Greek philosophers thought the bursts of light were the result of fire inside our heads: "The eye obviously has fire within it, for when the eye is struck fire flashes out," wrote Alcmaeon of Croton (6th–5th century BCE), a philosopher and early neuroscientist, of the swirls and specks someone sees after getting a blow to the head. A century later, Plato—who believed that a "visual current" [PDF] streamed out of the eye—wrote that "Such fire as has the property, not of burning, but of yielding a gentle light they [the Gods] contrived should become the proper body of each day."

Plato's take was still the dominant one through the Middle Ages. Eventually, Newton (1642–1727) theorized a concept that's more in line with what's believed today about these strange sparkly visions: The phenomenon is due to light that's produced and observed when pressure and motion is placed on the eyes.

Eleonora Lad, an associate professor of ophthalmology at Duke University Medical Center who has a background in neuroscience, explains exactly why eye rubbing generates these visions: "Most vision researchers believe that phosphenes result from the normal activity of the visual system after stimulation of one of its parts from some stimulus other than light," including putting external pressure on the eyes. (Interestingly, due to retinal damage, blind people can't see phosphenes caused by pressure, but they can see them when their visual cortex is electrically stimulated. In hopes of turning this phenomenon into improved vision for the blind, scientists have developed a cortical visual prosthesis, implanted in the visual cortex, that generates patterns of phosphenes. The device has been approved by the FDA for clinical trial.)

As Alcmaeon rightly pointed out, there are causes for the bursts of light beyond just rubbing your eyes: Getting hit in the eye can produce this phenomenon—as can a sneeze, a surprisingly powerful event that tends to clamp our eyes shut, Wen says.

Receiving an MRI or EEG may also trigger it. MRIs, for example, produce a changing magnetic field which can stimulate the visual cortex, making a person see these flashing lights. When it comes to an EEG, depending on the brain stimulation frequency band (Hz) used, some patients experience the phenomenon when closing their eyes, which is believed to come from retinal stimulation during the process.

And the activity doesn't only happen on Earth; astronauts in space have also been known to experience them. As reported in 2006 in the journal Vision Research, "over 80 percent of astronauts serving in today's NASA or ESA (European Space Agency) programs have perceived phosphenes at least in some missions and often over several orbits." They're mainly attributed to interactions between the eye and cosmic ray particles in space, outside the Earth's protective magnetic field.

No matter the cause, the bursts of light are perfectly normal—but that doesn't mean you should engage in excessive eye rubbing. Wen says ophthalmologists advise against rubbing your eyes or applying vigorous pressure; according to Lad, too much rubbing may be damaging to the cornea and lens or "result in a loss of fatty tissue around the eyes, causing the eyes to look deep-set."

Some Fish Eggs Can Hatch After Being Pooped Out by Swans

iStock/olaser
iStock/olaser

A question that’s often baffled scientists is how certain species of fish can sometimes appear—and even proliferate—in isolated bodies of water not previously known to harbor them. A new study has demonstrated that the most unlikely explanation might actually be correct: It’s possible they fell from the sky.

Specifically, from the rear end of a swan.

A study in the journal Ecology by researchers at the Unisinos University in Brazil found that killifish eggs can, in rare cases, survive being swallowed by swans, enduring a journey through their digestive tracts before being excreted out. This kind of fecal public transportation system explains how killifish can pop up in ponds, flood waters, and other water bodies that would seem an unlikely place for species to suddenly appear.

After discovering that some plants could survive being ingested and then flourish in swan poop, researchers took notice of a killifish egg present in a frozen fecal sample. They set about mixing two species of killifish eggs into the food supply of coscoroba swans living in a zoo. After waiting a day, they collected the poop and dug in looking for the eggs.

Of the 650 eggs they estimated to have been ingested by the swans, about five were left intact. Of those, three continued to develop. Two died of a fungal infection, but one survived, enduring 30 hours in the gut and hatching 49 days after being excreted.

Because killifish eggs have a thick outer membrane, or chorion, they stand a chance of coming through the digestive tract of an animal intact. Not all of what a swan ingests will be absorbed; their stomachs are built to extract nutrients quickly and get rid of the whatever's left so the birds can eat again. In rare cases, that can mean an egg that can go on to prosper.

Not all fish eggs are so durable, and not all fish are quite like the killifish. Dubbed the "most extreme" fish on Earth by the BBC, killifish have adapted to popping up in strange environments where water may eventually dry up. They typically live for a year and deposit eggs that can survive in soil, delaying their development until conditions—say, not being inside a swan—are optimal. One species, the mangrove killifish, can even breathe through its skin. When water recedes, they can survive on land for over two months, waddling on their bellies or using their tails to "jump" and eat insects. A fish that can survive on dry land probably doesn't sweat having to live in poop.

The researchers plan to study carp eggs next to see if they, too, can go through a lot of crap to get to where they’re going.

[h/t The New York Times]

8 Facts About the Animals of Chernobyl

iStock/Tijuana2014
iStock/Tijuana2014

Three decades after the Chernobyl disaster—the world’s worst nuclear accident—signs of life are returning to the exclusion zone. Wild animals in Chernobyl are flourishing within the contaminated region; puppies roaming the area are capturing the hearts of thousands. Tourists who have watched the critically acclaimed HBO series Chernobyl are taking selfies with the ruins. Once thought to be forever uninhabitable, the Chernobyl Exclusion Zone has become a haven for flora and fauna that prove that life, as they say in Jurassic Park, finds a way.

1. The animals of Chernobyl survived against all odds.

The effects of the radioactive explosion at the Chernobyl nuclear power plant on April 26, 1986 devastated the environment. Around the plant and in the nearby city of Pripyat in Ukraine, the Chernobyl disaster’s radiation caused the leaves of thousands of trees to turn a rust color, giving a new name to the surrounding woods—the Red Forest. Workers eventually bulldozed and buried the radioactive trees. Squads of Soviet conscripts also were ordered to shoot any stray animals within the 1000-square-mile Chernobyl Exclusion Zone. Though experts today believe parts of the zone will remain unsafe for humans for another 20,000 years, numerous animal and plant species not only survived, but thrived.

2. Bears and wolves outnumber humans around the Chernobyl disaster site.

While humans are strictly prohibited from living in the Chernobyl Exclusion Zone, many other species have settled there. Brown bears, wolves, lynx, bison, deer, moose, beavers, foxes, badgers, wild boar, raccoon dogs, and more than 200 species of birds have formed their own ecosystem within the Chernobyl disaster area. Along with the larger animals, a variety of amphibians, fish, worms, and bacteria makes the unpopulated environment their home.

3. Most Chernobyl animals don’t look any different from their non-Chernobyl counterparts.

Stray puppies play in an abandoned, partially-completed cooling tower inside the exclusion zone at the Chernobyl nuclear power plant
Sean Gallup, Getty Images

Tour guides tell visitors not to pet Chernobyl animals due to potential radioactive particles in their fur, but some biologists have been surprised that the incidence of physical mutations appears lower than the blast of radiation would have suggested. There have been some oddities recorded within the area—such as partial albinism among barn swallows—but researchers think that the serious mutations mostly happened directly after the explosion. Today’s wild animals are sporting their normal number of limbs and aren’t glowing.

4. Radiation may have killed off Chernobyl’s insects.

In contrast to the large carnivores and other big fauna, bugs and spiders have seen a big drop in their numbers. A 2009 study in Biology Letters indicated that the more radiation there was in certain locations around the Chernobyl disaster area, the lower the population of invertebrates. A similar phenomenon occurred after the 2011 nuclear accident at the Fukushima nuclear power plant. Bird, cicada, and butterfly populations decreased, while other animal populations were not affected.

5. Despite looking normal, Chernobyl's animals and plants are mutants.

There may be no three-headed cows roaming around, but scientists have noted significant genetic changes in organisms affected by the disaster. According to a 2001 study in Biological Conservation, Chernobyl-caused genetic mutations in plants and animals increased by a factor of 20. Among breeding birds in the region, rare species suffered disproportional effects from the explosion’s radiation compared to common species. Further research is needed to understand how the increased mutations affect species’ reproductive rates, population size, genetic diversity, and other survival factors.

6. The absence of humans is returning Chernobyl to wilderness.

As WIRED points out, the Chernobyl disaster presents an unintended experiment in what Earth would be like without humans. Hunting is strictly illegal and living within the Chernobyl Exclusion Zone is not recommended. The fewer humans there are, the more nature can re-establish itself unencumbered by human activity. According to The Guardian, an official nature reserve recently created on the Belorussian side of the zone claims to be “Europe’s largest experiment in rewilding,” where animals are losing their fear of humans. In fact, a few species are actually living better within the Chernobyl Exclusion Zone than outside of it. Wolves were found to be seven times as abundant on the premises than in other, non-radioactive areas. Moose, roe deer, red deer, and wild boar were found to have similar numbers within the CEZ as compared to those in three uncontaminated nature reserves in Belarus.

7. An endangered wild horse is making a comeback thanks to Chernobyl.

A Przewalski's horse lays in a meadow
PATRICK PLEUL, AFP/Getty Images

British ecologists Mike Wood and Nick Beresford, who specialize in studying the effects of radiation on Chernobyl’s wildlife, observed that the Przewalski’s horse—an endangered wild species that originated in Mongolia—is thriving within the CEZ. In the late 1990s, about 30 Przewalski’s horses were released in the Ukrainian side of the CEZ. Based on camera trap images, Wood estimated that some of the original horses (identified by their brand markings) are still alive. Photos of juvenile horses and foals also indicated that the population is expanding.

8. You can adopt a Chernobyl puppy.

Hundreds of pooches—the descendants of dogs abandoned by their owners during the site’s evacuation on April 27, 1986—have made the desolate area their home. Until 2018, it was illegal to bring any animal out of the zone due to the risk of radiation contamination. But now, puppies cleared of radiation are getting a chance to find their forever homes. Spearheaded by the Clean Futures Fund and SPCA International, the management and adoption program ensures that the stray dogs are spayed, neutered, and vaccinated so they will be healthy and ready for adoption.

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