title: Eyelashes divert airflow to protect the eye.
abstract: Eyelashes are ubiquitous, although their function has long remained a mystery. In this study, we elucidate the aerodynamic benefits of eyelashes. Through anatomical measurements, we find that 22 species of mammals possess eyelashes of a length one-third the eye width. Wind tunnel experiments confirm that this optimal eyelash length reduces both deposition of airborne particles and evaporation of the tear film by a factor of two. Using scaling theory, we find this optimum arises because of the incoming flow's interactions with both the eye and eyelashes. Short eyelashes create a stagnation zone above the ocular surface that thickens the boundary layer, causing shear stress to decrease with increasing eyelash length. Long eyelashes channel flow towards the ocular surface, causing shear stress to increase with increasing eyelash length. These competing effects result in a minimum shear stress for intermediate eyelash lengths. This design may be employed in creating eyelash-inspired protection for optical sensors.
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Guillermo J
authors.initials: GJ
authors.lastname: Amador
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Mao
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: DeMercurio
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Carmen
authors.initials: C
authors.lastname: Montero
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Joel
authors.initials: J
authors.lastname: Clewis
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Alexeev
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA School of Biology, Georgia Institute of Technology, Atlanta, GA, USA hu@me.gatech.edu.
authors.forename: David L
authors.initials: DL
authors.lastname: Hu
mesh_terms: D000392:Air Movements; D000818:Animals; D001696:Biomechanical Phenomena; D005123:Eye / Q000033:anatomy & histology*; D005140:Eyelashes / Q000502:physiology*; D006801:Humans; D008322:Mammals / Q000033:anatomy & histology*; D008962:Models, Theoretical; D009799:Ocular Physiological Phenomena; D013045:Species Specificity; D014870:Water Loss, Insensible / Q000502:physiology*
keywords: bristles; evolution; filter; porous