72th Annual Meeting of the APS Division of Fluid Dynamics (November 23, 2019 — November 26, 2019)

P0033: Tear Dynamics: Happy or Sad?

  • Ekaterina Brovina, Penn State University
  • Cooper Kovar, Penn Sate University
  • Heidi Reuter, Penn State University
  • Azar Eslam-Panah, Penn Sate University
DOI: https://doi.org/10.1103/APS.DFD.2019.GFM.P0033

A salty, clear liquid full of protein, water, mucus, and oil from your eye, which flows down across your face is better known as “tear”. There are three types of tears. First is basal tears, which keep your eyes from drying out completely. Basal tears are omnipresent in our eyes. These constant tears are what keep our eyes from drying out completely. Second type is reflex tears, which serve to protect the human eye and cornea. Your eyes release them in larger amounts than basal tears, and they may contain more antibodies to help fight bacteria. The last type of tears is emotional tears. It all starts in the cerebrum where sadness is registered. Emotional tears contain additional hormones and proteins not present in basal or reflex tears. Scientists have showed that the human tear film has non-Newtonian properties. The shape and motion of millimeter-sized tear drops sliding down the face in a situation of partial wetting is studies here. The tear drops start moving at a steady velocity. However, gravity and viscosity effects are wrestling with each other in this situation. Therefore, the tear drops change their aspect ratio: they become longer and thinner, but maintain a constant, millimeter-scale height. As their aspect ratio changes, a threshold is reached at which the drops are no longer rounded but develop a ‘corner’ at their rear.

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