Through experiments, we observed that eyelashes reduce evaporation of the tear film and deposition of particles onto the eye by 50%. With the tear film being only 3 micrometers thick, protecting it from drying out is critical. Additionally, airborne pathogens, spread through pollen, animal dander, dust mites or droplets spread through sneezing and coughing, can cause eye infections, like pink eye or conjunctivitis.

Below we show two videos generated by our collaborators Wenbin Mao and Alexander Alexeev. In the videos we show the trajectories of particles following the streamlines of airflow moving towards the eye surface. The top video shows an eye without eyelashes, and the one below shows an eye with eyelashes of optimal length. We see that fewer particles reach the eye surface when eyelashes are present.

Eyelashes and eyelash-inspired porous arrays can help protect sensitive surfaces from dirty airflows, like the dust storm shown below.

Mammals possess an array of hairs surrounding their eyes, commonly referred to as eyelashes. We have investigated the role of eyelashes in protecting the wet eye of mammals from drying and accumulating particles. From anatomical measurements of 22 physiologically diverse mammals, we find that eyelashes have a length of approximately one-third the eye’s width. Wind tunnel experiments show that this particular length results in a minimum value for tear film evaporation and contamination. Numerical simulation and aerodynamic theory reveal two competing aerodynamic effects from which this optimum arises: short lashes create a stagnation zone above the eye surface, whereas long lashes channel flow towards the eye. Eyelashes serve as the eye’s first line of defense, complementing the sophisticated tear duct system, and possibly reducing the frequency of blinks.