Eyelashes are typically one-third the length of the eye’s width. This is not simply due to chance for this length is the ideal length for eyelashes to do their job. A length of one-third in relation to the eye is sufficient to create an air buffer above the cornea. The buffer reduces the air flow, to prevent the eye from excessively drying out. In addition to this, the eyelash also cuts down on the number of airborne particles that could potentially land on the eye.
For the research, scientists measured the eyelash and eye lengths of 22 mammalian species, ranging from armadillos and hedgehogs and to giraffes and kangaroos. To add to the mix, people were also included. In each case it was found that the lengths of the animals’ eyelashes were proportional to eye size. Here, the length averaged one-third of the eye’s width.
The study was performed by scientists working at the Georgia Institute of Technology. The new findings have been reported to the Journal of the Royal Society Interface. The research study is titled “Eyelashes divert airflow to protect the eye.”
Using these data, The New York Times recounts that the scientists constructed computational models and went on to demonstrate that lashes of the length seen in nature reduced the incoming air flow to the eye surface by half compared to having no lashes at all. Here, the optimal-length lashes created the greatest boundary layer of air around the eye’s surface, while longer lashes directed air into the eye.
Next, as National Geographic has noted, to show whether the computer predictions were correct, the scientists tested the theory by using a wind tunnel and an eye model. For this, a small water-filled aluminum dish with the same dimensions as the surface as a human eye, surrounded by lashes of synthetic mesh, which behaved comparably to commercially available human hair lashes, was deployed.
With the model, the research group measured eye evaporation during 10 minutes of wind tunnel exposure using a sensitive scale and found the same protective effect their models had predicted. At the same time, the researchers tested how lashes protected the eye from airborne particles by filling the wind tunnel with fluorescent dust-sized particles floating in heavy humidifier fog. Optimal-length lashes were again shown to protect the eye by reducing the number of particles captured on absorbent paper on the eye model’s surface by 50 percent.
