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Eyelashes Grow To Just The Right Length To Shield Eyes

A calf sports platinum blonde lashes.

Attaching fake eyelashes might make give you a few extra millimeters to bat at your date, but they could also be channeling dust into your eyes. That's because the ideal eyelash length is about one third the width of an eye. And that goes for 22 different animals, not just humans.

A group of researchers at Georgia Tech found the ideal eyelash ratio after measuring pelts at the American Museum of Natural History. "They take great pride in their preservation of the pelt, all the hair and all the fur," says Guillermo Amador, a doctoral student in fluid mechanics at Georgia Tech and the lead author of the study, published Wednesday in the Journal of the Royal Society Interface.

One of his collaborators carefully measured the width of each eye and the length of the eyelashes on 22 different mammals, including species of camel, kangaroo, panda and armadillo.

The mammals measured included rabbit, goat, elephant, warthog, possum, elephant shrew, Baird's tapir, red kangaroo, leopard and porcupine.

So what happens when a fluid mechanics lab embarks on an eye study? They salvage the fan from a desktop computer and use it to build an adjustable wind tunnel, of course! "We used two different airflows that are right in the range that animals will experience when they're just walking at cruising speed in the air," Amador tells Shots.

To see how quickly an eye dries out, the researchers measured the mass of a small eye-sized dish to see how quickly water evaporates.

For the dust test, they added fluorescent dye to a humidifier and measured how much dye landed on an eye-sized piece of absorbent paper.

They tested false eyelashes and a porous mesh, and found that they both behaved the same way. Then they tested varying lengths of mesh to determine how the length of an animal's eyelashes affects how fast the eye dries out and how much dust gets in.

"As [the eyelashes] get longer you get less evaporation and less deposition," says Amador. This means wetter, cleaner eyes. "But if they get too long they start to channel more airflow towards the eye and that increases the evaporation and increases the deposition of the particles."

The curvature of the eyelashes doesn't seem to matter as much. Animal eyelashes vary greatly: camel lashes, for instance, angle downward, almost parallel to the surface of the eye. Amador and his colleagues measured length perpendicular to the surface of the eye to control for these differences.

But don't go trying to extend or trim your eyelashes to the perfect length. "Nature's kind of taken care of that for us," says Amador.

Eyelashes allow animals to keep their eyes open when they need to watch for predators or prey, so it makes sense that most eyelashes would reach a perfect length to minimize drying and dust.

"If women use false eyelashes they could actually dry out their eyes a little faster and have to blink more frequently," Amador says. Maybe all the flirtatious eyelash-batters of the world just have seriously dry eyes.

Still, Amador is enthusiastic about the potential applications of his findings for people with madarosis, which means loss of eyelashes due to health problems. "They do get eye infections more often," he says. In this case, donning false eyelashes could help. "It would give them a kind of protection from the elements."

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

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