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]

FDA Recalls Thyroid Medications Due to Contamination Risk

iStock
iStock

Hypothyroid medications manufactured by Westminster Pharmaceuticals have been recalled after it was discovered that one of the company’s Chinese suppliers failed to meet U.S. Food and Drug Administration (FDA) standards, CNN reports.

The oral tablets contain levothyroxine (LT4) and liothyronine (LT3), which are both synthetic hormones used to treat thyroid conditions.

The medicine was recalled as a precaution after it was discovered during a 2017 FDA inspection that the Chinese supplier in question, Sichuan Friendly Pharmaceutical Co., was not practicing good manufacturing practices.

However, patients with serious thyroid conditions shouldn’t throw out their pills just yet. No adverse effects from the medication have been reported, and the risk of not taking the medication outweighs the risk of taking a recalled pill.

According to the FDA, “Because these products may be used in the treatment of serious medical conditions, patients taking the recalled medicines should continue taking their medicine until they have a replacement product.”

For more information on the specific lots and products in question, visit the FDA’s website.

[h/t CNN]

A 'Zombie Gene' Might Be the Reason Elephants Rarely Get Cancer

iStock
iStock

When it comes to cancer rates in the animal kingdom, elephants are an anomaly. As Popular Science notes, cancer should be more common among larger species, but with elephants, that simply isn’t the case. Only about 5 percent of elephants die from cancer, compared to 11 to 25 percent of humans.

In a new study, published in Cell Reports, University of Chicago researchers found what’s believed to be the genetic source of elephants’ cancer immunity. Elephants, like all mammals, have a gene called LIF that is known to suppress tumors. Humans have one copy of this gene, but elephants have 10 copies, which have developed over 80 million years of evolution. However, only one of those copies, called LIF6, is functional in elephants.

The other LIF copies are essentially dead because they lack a specific piece of DNA to make them function. At some point during the evolutionary process, the LIF6 gene copy turned back on, but scientists don’t know why or when this occurred. This “zombie gene” helps kill mutated cells, in true Night of the Living Dead fashion.

“This reanimation of LIF6 occurred perhaps over 59 million years,” Joshua Schiffman, who studies cancer in elephants but was not involved in the study, told Popular Science. “That’s an amazingly long period of time for nature to modify and perfect an anticancer mechanism.”

Scientists aren’t yet sure how this could be applied to cancer research in humans, but they say it’s a promising start and a creative approach to the problem. While these findings are still fresh and need to be duplicated, it raises the possibility of creating a drug that mimics the function of LIF6.

[h/t Popular Science]

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios