Long eyelashes adds beauty to eyes, but it’s bad according to a new study.
Eyelashes are ubiquitous features of the eyes of mammals and have been speculated to act as ’dust catchers’ to protect the moist and sensitive cornea.
In this study, we discover the aerodynamic mechanism whereby eyelashes minimize air flow across the ocular surface without obstructing vision.
Measurements of 22 phylogenetically diverse species of mammals, from hedgehogs to giraffes, indicate eyelash length is tuned to a length of approximately one-third the eye width.
Wind tunnel experiments using eyelash-inspired synthetic meshes show eyelashes of the appropriate length reduce both evaporation rates and particle deposition by 50 percent.
Numerical simulations and viscous flow theory reveal two competing aerodynamic resistances for incoming flow: airflow through the lashes is resisted by viscous drag, or alternatively, airflow turns to flow around the lashes and is resisted by the pressure of the incoming flow.
Our modeling shows that at the observed optimal eyelash length, these two resistances are equal and at a local maximum, suggesting a minimal flow rate at the eye surface.
The ability for eyelashes to protect the eye can motivate bio-inspired solutions for passive and scalable dust control of optical sensors.