Anything shorter or longer, including the fake eyelashes that are popular in Hollywood and make-up aisles, increases airflow around the eye and leads to more dust hitting the surface.

"Eyelashes form a barrier to control airflow and the rate of evaporation on the surface of the cornea," said Guillermo Amador from George W. Woodruff school of mechanical engineering who authored the study.

"When eyelashes are shorter than the one-third ratio, they have only a slight effect on the flow. Their effect is more pronounced as they lengthen up until one-third. After that, they start funneling air and dust particles into the eye," he cautioned.

To reach this conclusion, Amador and the research team sent a student to the American Museum of Natural History in New York to measure eyes and eyelashes of various animals.

A four-millimetre deep, 20-millimetre diameter aluminium dish served as the cornea.Mesh surrounded the dish to replicate the eyelashes.They discovered the ideal ratio while varying the mesh length during evaporation and particle deposition studies.

The study was published in the Journal of the Royal Society Interface.


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