Fake eyelashes may be damaging eye health

Wearing long, fake eyelashes may lead more air and dust to hit the eyes causing them to dry out, a new study suggests.
Scientists have found that 22 species of mammals - from humans to giraffes - have evolved eyelashes that are one third the width of their eye to protect from dust and moisture evaporation.
Eyelashes shorter or longer than one third the width of the eye increase airflow around the eye and lead 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, a Georgia Tech PhD candidate in the 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 funnelling air and dust particles into the eye," Amador said.
Amador and the research team led by Assistant Professor David Hu, sent a student to the American Museum of Natural History in New York in 2012 to measure eyes and eyelashes of various animals.

Aside from an elephant, which has extremely long eyelashes, every species studied had evolved to the same ratio of lash length to eye width.

The team then built the wind tunnel to re-create air flows on a mimic of an adult, human eye.
A 4-millimetre deep, 20-millimetre diameter aluminum dish served as the cornea. It sat on top of an acrylic plate, which imitated the rest of the face. Mesh surrounded the dish to replicate the eyelashes.
"As short lashes grew longer, they reduced air flow, creating a layer of slow-moving air above the cornea," said Hu.
"This kept the eye moist for a longer time and kept particles away. The majority of air essentially hit the eyelashes and rolled away from the eye," Hu added.

The opposite process occurred with longer eyelashes. The lashes extended further into the airflow and created a cylinder. The air and its molecules channelled toward the eye and led to faster evaporation.
"This is why long, elegant, fake eyelashes aren't ideal. They may look good, but they're not the best thing for the health of your eyes," said Amador.
The research team noted that people who can't grow eyelashes could wear fake ones, if they're the correct length, for extra protection and to reduce dry eye.
"Even if they're not the correct length, more eyelashes are always better than less," said Alexander Alexeev, an associate professor in the School of Mechanical Engineering.

"If fake eyelashes are dense enough, they may give the same overall effect in protecting the eye even if they are longer than one-third," Alexeev said.
The study is published in the Journal of the Royal Society Interface.