A recent study suggests that eyelashes have an optimum length and evolved for keeping the eyes from drying out.
The actual purpose of having eyelashes has long been unknown. Some theories believe that eyelashes protect the eye from dust in the air, while some suggest that they identify foreign particles before they enter the eye and make the eye blink before any damage is done.
However, David Hu at the Georgia Institute of Technology, who is co-author of the study, said that the delicate hair on the eyelids also have a purpose to keep the eyes moist.
Hu explained that the latest study involved studying the eyelashes of about 22 mammals. The study measured the size of eyelashes in these mammals and found that the length of eyelashes was normally about a third of the width of the eyes. This ratio of the eyelashes keeps the eye moist.
"We found that there's a pretty good trend for how lashes change with eye width," said Hu. "That's quite striking because in the mammal-hair literature, you don't see many trends. Hair is usually a function of habitat, activity, things like that."
The researchers also conducted experiments to find how quickly moisture evaporates from the eyes with different sizes of eyelashes. The study found that an optimal size of eyelashes prevents moisture evaporation from the eyes by about 50 percent.
Hu reported that people who do not have eyelashes suffer from a higher rate of eye infection in comparison to people who do have eyelashes, suggesting that these delicate hairs have some protective function for the eyes. It is important to have the optimal size of eyelashes to ward off particles that may be harmful to the eye. Extra-long eyelashes are also not good as they may funnel air to the eyes, which may cause faster drying of eyes.
Hu also said that denser eyelashes of an optimal size are more beneficial to the eyes. False eyelashes, for instance, have been used for long by women to look beautiful and attractive. Fake lashes are usually available in various sizes and colors.
Researchers therefore suggest that people who suffer from frequent dry eyes use false eyelashes to keep their eyes moist.
The study was published in The Royal Society's journal Interface.
