Eyelashes grow in ideally protective proportion, study finds
The mysterious function of eyelashes has been revealed at last – thanks to science.
After measuring the dimensions of nearly two dozen mammal eyes, performing a series of wind tunnel experiments and engaging in some complex fluid dynamic modeling, researchers determined that most mammal eyelashes are one-third the length of their eyes – just the right length to minimize the flow of air over the eyeball.
This reduction of airflow is important because less moving air across the eye keeps evaporation at bay and stops irritating dust from getting deposited on the eye surface, the scientists report in a study published this week in the Journal of the Royal Society Interface.
“All mammals have wet eyes, and airflow is the enemy of that,” said Guillermo Amador, a doctoral student at the Georgia Institute of Technology, and the first author on the paper.
The comprehensive research into eyelash function began in 2012, after senior author David Hu’s daughter was born with long, batting eyelashes, leading him to wonder about their function.
Hu, a mechanical engineer at the Georgia Institute of Technology, has been inspired by his young children before. The idea for a previously published study that found most mammals take 21 seconds to urinate, came to him while changing a diaper.
To find out what made the one-third ratio so special, the researchers built a wind tunnel to mimic the airflow an animal would encounter while moving at a walking pace. They also constructed a fake eye out of a shallow aluminum pan 2 centimeters across. Over a series of experiments, they surrounded the eye with a plastic mesh, then fake eyelashes made from human hair.
Mesh and fake eyelashes gave the same result. The researchers found that the protection these “eyelashes” gave to the eye increased as they grew longer, until they hit the optimum length of one-third the width of the eye. Beyond that length, evaporation and the deposition of dust particles went up.
There may be practical applications to this work. For example, the authors say solar panels or sensors that take in light could benefit from being surrounded by eyelash-inspired filters to keep dust from landing.