ABSTRACT
INTRODUCTION The ability to produce tear fl uid to protect the eye from physical, chemical or pathogenic harm is found in almost every species, including mammals, birds, and reptiles. A human being produces between 0.5 and 2.0 μl of tear
1Martin Luther University Halle-Wittenberg, Department of Anatomy and Cell Biology, Grosse Steinstraße 52, 06097 Halle (Saale), Germany; E-mail: julia@dieckow.de 2Schepens Eye Research Institute, Massachusetts Eye and Ear, Harvard Medical School, 20 Staniford Street, Boston, MA 02114; E-mail: pablo.argueso@schepens.harvard.edu *Corresponding author
fl uid per minute (Clinch et al. 1983). It is spread over the ocular surface during blinking, which happens every three to six seconds while awake (Sforza et al. 2008). The permanently renewed tear fi lm has to fulfi ll a variety of tasks. In the following chapter, the structure, composition and functions of this unique fl uid will be further described.
