The Math Behind the Classic Eye Chart Is Surprisingly Complex


Next time you're forced to take a vision exam at the DMV, take a moment to appreciate the complex math that went into the eye chart. What seems like a fairly straightforward way to assess eyesight is actually the result of specific calculations that can tell you a lot about how the human eye works.

As The Verge explains in the video below, eye charts measure one aspect of healthy vision: visual acuity. This is our ability to make out fine details in our surroundings—kind of like the resolution of a computer screen, but instead of pixels, it's measured in degrees. It's easy for our eyes to tell the difference between two points of light coming from different directions, but if those points start to move closer together they will eventually blur into one. The angle created just as two lines of light become too close for our eyes to distinguish them is called the resolution limit. In healthy adults, it measures one-sixtieth of a degree, or one arcminute wide.

When a doctor asks you to read an eye chart, the resolution limit is what they're looking for. The letters in the middle of an eye chart are all designed to be exactly one arcminute thick. If your vision is sharp, you should be able tell the difference between the white spaces and the black lines of the text from 20 feet away. 

A perfect 20/20 score on an eye chart test doesn't mean you have perfect vision: Visual acuity, along with color, contrast, and depth perception, are all important parts of healthy eyesight. And a higher resolution limit isn't always a sign of a permanent problem: For people who spend their days staring at a screen, it may be caused by the eye fatigue brought on by Computer Vision Syndrome. If this is a problem for you, here are some ways to tweak your behavior.

[h/t The Verge]

One Good Reason Not to Hold in a Fart: It Could Leak Out of Your Mouth


The next time you hold in a fart for fear of being heard by polite company, just remember this: It could leak out of your mouth instead of your butt. Writing on The Conversation, University of Newcastle nutrition and dietetics professor Clare Collins explains that pent-up gas can pass through your gut wall and get reabsorbed into your circulation. It's then released when you exhale, whether you like it or not.

“Holding on too long means the build up of intestinal gas will eventually escape via an uncontrollable fart,” Collins writes. In this case, the fart comes out of the wrong end. Talk about potty mouth.

A few brave scientists have investigated the phenomenon of flatulence. In one study, 10 healthy volunteers were fed half a can of baked beans in addition to their regular diets and given a rectal catheter to measure their farts over a 24-hour period. Although it was a small sample, the results were still telling. Men and women let loose the same amount of gas, and the average number of “flatus episodes” (a single fart, or series of farts) during that period was eight. Another study of 10 people found that high-fiber diets led to fewer but bigger farts, and a third study found that gases containing sulphur are the culprit of the world’s stinkiest farts. Two judges were tapped to rate the odor intensity of each toot, and we can only hope that they made it out alive.

Scientific literature also seems to support Collins’s advice to “let it go.” A 2010 paper on “Methane and the gastrointestinal tract” says methane, hydrogen sulfide, and other gases that are produced in the intestinal tract are mostly eliminated from the body via the anus or “expelled from the lungs.” Holding it in can lead to belching, flatulence, bloating, and pain. And in some severe cases, pouches can form along the wall of the colon and get infected, causing diverticulitis.

So go ahead and let it rip, just like nature intended—but maybe try to find an empty room first.

[h/t CBS Philadelphia]

A Chemical in Spider Venom Could Be a Key to Killing Skin Cancer Cells

Alan Couch, Flickr // CC BY 2.0
Alan Couch, Flickr // CC BY 2.0

Despite their formidable reputation in the eyes of arachnophobes, spiders contribute to human society in a number of positive ways. On a practical level, they can reduce the population of insects in your home by trapping them for meals. Outdoors, they keep pests from destroying gardens and crops, making sure we don't slip into a period of famine and anarchy. In the lab, scientists have identified a number of chemicals in their venom as possible building blocks for medicines treating everything from pain to muscular dystrophy.

That field of study has led to a promising discovery. In Australia, researchers have isolated one particular compound in a funnel-web spider's venom that can diminish skin cancer cells.

Scientists at QIMR Berghofer and the University of Queensland began studying the Australian funnel-web spider known as Hadronyche infensa after a similar Brazilian arachnid, Acanthoscurria gomesiana, was shown to carry a peptide in its venom called gomesin that has cancer-fighting properties. Identifying a similar peptide in the Australian spider, the researchers demonstrated that the chemical was effective in killing skin cancer cells while leaving healthy skin cells alone.

The peptide was tested on human melanoma cells, eradicating the majority of them. In mice, it also slowed the growth of the melanomas. The peptide was even effective in killing cells found in facial tumors of Tasmanian devils, a marsupial susceptible to an aggressive form of skin cancer transmittable through biting. The results were published in the journal Scientific Reports.

These peptides are able to be manipulated, taking on different properties as scientists alter amino acids to create new and potentially more potent versions. It’s hoped that this line of research will lead to the development of treatments for skin cancer in humans.

It's something to think about the next time you consider swatting a spider—though if you happen to reside in Australia and see the funnel-web variety, you might not have a choice. While there are 35 different species of funnel-webs of varying potency, some are so formidable that their fangs can pierce fingernails, and their venom is able to kill a human in less than 15 minutes.

[h/t New Atlas]