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."

12 Creative Ways to Spend Your FSA Money Before the Deadline

stockfour/iStock via Getty Images
stockfour/iStock via Getty Images

If you have a Flexible Spending Account (FSA), chances are, time is running out for you to use that cash. Depending on your employer’s rules, if you don’t spend your FSA money by the end of the grace period, you potentially lose some of it. Lost cash is never a good thing.

For those unfamiliar, an FSA is an employer-sponsored spending account. You deposit pre-tax dollars into the account, and you can spend that money on a number of health care expenses. It’s kind of like a Health Savings Account (HSA), but with a few big differences—namely, your HSA funds roll over from year to year, so there’s no deadline to spend it all. With an FSA, though, most of your funds expire at the end of the year. Bummer.

The good news is: The law allows employers to roll $500 over into the new year and also offer a grace period of up to two and a half months to use that cash (March 15). Depending on your employer, you might not even have that long, though. The deadline is fast approaching for many account holders, so if you have to use your FSA money soon, here are a handful of creative ways to spend it.

1. Buy some new shades.

Head to the optometrist, get an eye prescription, then use your FSA funds to buy some new specs or shades. Contact lenses and solution are also covered.

You can also buy reading glasses with your FSA money, and you don’t even need a prescription.

2. Try acupuncture.

Scientists are divided on the efficacy of acupuncture, but some studies show it’s useful for treating chronic pain, arthritis, and even depression. If you’ve been curious about the treatment, now's a good time to try it: Your FSA money will cover acupuncture sessions in some cases. You can even buy an acupressure mat without a prescription.

If you’d rather go to a chiropractor, your FSA funds cover those visits, too.

3. Stock up on staples.

If you’re running low on standard over-the-counter meds, good news: Most of them are FSA-eligible. This includes headache medicine, pain relievers, antacids, heartburn meds, and anything else your heart (or other parts of your body) desires.

There’s one big caveat, though: Most of these require a prescription in order to be eligible, so you may have to make an appointment with your doctor first. The FSA store tells you which over-the-counter items require a prescription.

4. Treat your feet.

Give your feet a break with a pair of massaging gel shoe inserts. They’re FSA-eligible, along with a few other foot care products, including arch braces, toe cushions, and callus trimmers.

In some cases, foot massagers or circulators may be covered, too. For example, here’s one that’s available via the FSA store, no prescription necessary.

5. Get clear skin.

Yep—acne treatments, toner, and other skin care products are all eligible for FSA spending. Again, most of these require a prescription for reimbursement, but don’t let that deter you. Your doctor is familiar with the rules and you shouldn’t have trouble getting a prescription. And, as WageWorks points out, your prescription also lasts for a year. Check the rules of your FSA plan to see if you need a separate prescription for each item, or if you can include multiple products or drug categories on a single prescription.

While we’re on the topic of faces, lip balm is another great way to spend your FSA funds—and you don’t need a prescription for that. There’s also no prescription necessary for this vibrating face massager.

6. Fill your medicine cabinet.

If your medicine cabinet is getting bare, or you don’t have one to begin with, stock it with a handful of FSA-eligible items. Here are some items that don’t require a prescription:

You can also stock up on first aid kits. You don’t need a prescription to buy those, and many of them come with pain relievers and other medicine.

7. Make sure you’re covered in the bedroom.

Condoms are FSA-eligible, and so are pregnancy tests, monitors, and fertility kits. Female contraceptives are also covered when you have a prescription.

8. Prepare for your upcoming vacation.

If you have a vacation planned this year, use your FSA money to stock up on trip essentials. For example:

9. Get a better night’s sleep.

If you have trouble sleeping, sleep aids are eligible, though you’ll need a prescription. If you want to try a sleep mask, many of them are eligible without a prescription. For example, there’s this relaxing sleep mask and this thermal eye mask.

For those nights you’re sleeping off a cold or flu, a vaporizer can make a big difference, and those are eligible, too (no prescription required). Bed warmers like this one are often covered, too.

Your FSA funds likely cover more than you realize, so if you have to use them up by the deadline, get creative. This list should help you get started, and many drugstores will tell you which items are FSA-eligible when you shop online.

10. Go to the dentist.

While basics like toothpaste and cosmetic procedures like whitening treatments aren’t FSA eligible, most of the expenses you incur at your dentist’s office are. That includes co-pays and deductibles as well as fees for cleanings, x-rays, fillings, and even the cost of braces. There are also some products you can buy over-the-counter without ever visiting the dentist. Some mouthguards that prevent you from grinding your teeth at night are eligible, as are cleaning solutions for retainers and dentures.

11. Try some new gadgets.

If you still have some extra cash to burn, it’s a great time to try some expensive high-tech devices that you’ve been curious about but might not otherwise want to splurge on. The list includes light therapy treatments for acne, vibrating nausea relief bands, electrical stimulation devices for chronic pain, cloud-connected stethoscopes, and smart thermometers.

12. Head to Amazon.

There are plenty of FSA-eligible items available on Amazon, including items for foot health, cold and allergy medication, eye care, and first-aid kits. Find out more details on how to spend your FSA money on Amazon here.

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How Much Is the Earth Worth?

The New York Public Library, Unsplash
The New York Public Library, Unsplash

Our home planet may be the most precious place we know, but it isn't priceless. The Earth's resources and the value it offers to humans add up to some unknown, tangible cost. The species may never have to worry about buying or selling the world, but thinking of it in terms of concrete numbers can help us better understand its value. Now, as Treehugger reports, one scientist has developed a special formula that allows us to do just that.

According to the calculations of Greg Laughlin, an assistant astronomy and astrophysics professor from the University of California, Santa Cruz, the Earth is worth roughly $5 quadrillion (or $5,000,000,000,000,000). He came up with that price after gauging the planet's mass, temperature, age, and other factors that directly correlate to its ability to sustain life.

To emphasize just how valuable the Earth is, Laughlin also estimated the worth of other planets in our solar system. Our nearest neighbor Mars costs about the same as a used car at $16,000. That's a fortune compared to Venus, which he appraised at the meager value of one cent.

Laughlin doesn't expect these numbers to have applications in the real world. Rather, he hopes they will inspire people to better appreciate the only home they know. He's not the first person to put a massive, hypothetical price tag on something just for fun. The cost of the Death Star from Star Wars has been calculated at $852 quadrillion—many times Laughlin's estimate for Earth.

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