iStock
iStock

The Math Behind the Classic Eye Chart Is Surprisingly Complex

iStock
iStock

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]

nextArticle.image_alt|e
iStock
Netherlands Officials Want to Pay Residents to Bike to Work
iStock
iStock

Thinking about relocating to the Netherlands? You might also want to bring a bike. Government officials are looking to compensate residents for helping solve their traffic congestion problem and they want businesses to pay residents to bike to work, as The Independent reports.

Owing to automobile logjams on roadways that keep drivers stuck in their cars and cost the economy billions of euros annually, Dutch deputy infrastructure minister Stientje van Veldhoven recently told media that she's endorsing a program that would pay employees 19 cents for every kilometer (0.6 miles) they bike to work.

That doesn't sound like very much, but perhaps citizens who need to trek several miles each way would appreciate the cumulative boost in their weekly paychecks. For employers, the benefit would be a healthier workforce that might take fewer sick days and reduce parking needs.

Veldhoven says she also plans on designing a program that would assist employers in supplying workers with bicycles. The goal is to have 200,000 people opting for manual transportation over cars. If the program proceeds, it might find a receptive population. The Netherlands is already home to 22.5 million bikes, more than the 17.1 million people living there. In Amsterdam, a quarter of residents bike to work.

There's no timeline for implementing the pay-to-bike plan, but early trial studies indicate that the expense might not have to be a long-term prospect. Study subjects continued to bike to work even after the financial rewards stopped.

[h/t The Independent]

nextArticle.image_alt|e
iStock
New Health-Monitoring Litter Box Could Save You a Trip to the Vet
iStock
iStock

Unsure if your cat is sick or just acting aloof per usual? A “smart toilet” for your fur baby could help you decide whether a trip to the vet is really necessary.

Enter the Pet Care Monitor: More than a litter box, the receptacle is designed to analyze cat urine for health issues, The Asahi Shimbun in Tokyo reports. Created by the Japan-based Sharp Corporation—better known for consumer electronics such as TVs, mobile phones, and the world's first LCD calculator—the product will be available for purchase on the company’s website starting July 30 (although shipping limitations may apply).

Sensors embedded in the monitor can measure your cat’s weight and urine volume, as well as the frequency and duration of toilet trips. That information is then analyzed by an AI program that compares it to data gleaned from a joint study between Sharp Corp and Tottori University in Japan. If there are any red flags, a report will be sent directly to your smartphone via an application called Cocoro Pet. The monitor could be especially useful for keeping an eye on cats with a history of kidney and urinary tract problems.

If you have several cats, the company offers sensors to identify each pet, allowing separate data sets to be collected and analyzed. (Each smart litter box can record the data of up to three cats.)

The Pet Care Monitor costs about $225, and there’s an additional monthly fee of roughly $3 for the service. Sharp Corporation says it will continue developing health products for pets, and it has already created a leg sensor that can tell if a dog is nervous by measuring its heart and respiratory rates.

[h/t The Asahi Shimbun]

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios