The effect of a shear force on the cell shedding rate of the corneal epithelium

Abstract

ABSTRACT.Purpose: During blinking the lids apply a shear force to the corneal epithelium. The aim of this study was to determine if a shear force applied to the epithelial surface increases the rate at which cells shed. Methods: The shedding rate was studied in perfused whole rabbit eyes, and the effect of a shear force examined by exposing the corneas to a stirred solution. Control corneas were exposed to a static solution. The shedding rate and size of shed cells were measured, and the number of terminally differentiated cells on the corneal surface determined after 6 h of perfusion using ethidium bromide. Results: Compared with controls, the shear force increased the cell shedding rate from the corneal surface significantly (p < 0.01, paired t-test). The increase was due to small cells with a longest dimension less than 25 pm. The number of terminally differentiated cells on the epithelial surface did not increase. Conclusiom Because of the decrease in size, and the change in appearance of shedding cells, it is proposed that the increase in cell shedding rate was due to an increase in the number of apoptotic cells, and not to an increase in terminally differentiated cells. It is suggested that in the human eye, under adverse conditions, shear forces due to blinking may play a role in creating apoptotic cells.

Formulation and process factors influencing product quality and in vitro performance of ophthalmic ointments

“…More recent view on the structure of the tear film, however, combines the aqueous layer and mucin layer into one (aqueous-mucin layer) that exhibits a progressively low mucin concentration towards anterior lipid/air interface (Rolando and Zierhut, 2001). Nevertheless, this layer of tear film is widely considered as to not only supply all the necessary nutrients to the beneath cornea, but also to reduce friction during eyelid blinking motion (Inatomi et al, 1995), where the eyelid moves across the ocular surface at a very high speed (maximum of 17-20 cm/s (Doane, 1980)) and frequently (15-20 times per minute (Ren and Wilson, 1997)). The reported value for the thickness of the tear film varies depending on the principle of measurement, but is in the range of 3 to 40 µm (Bron et al, 2004;Werkmeister et al, 2013).…”

Elastohydrodynamics of the Eyelid Wiper

“…The rate of shedding of epithelial cells on the cornea is related to the magnitude of the shear forces (Ren and Wilson, 1997). Hence, the model provides a connection between blink dynamics and corneal cell shedding rates.…”

“…Nevertheless, the surface shear stress may still play a role in cell shedding of the corneal epithelium (Ren and Wilson, 1997). Hence, in the following, expressions for the surface shear stress are given.…”

Corneal epithelial cells exposed to shear stress show altered cytoskeleton and migratory behaviour

“…However, while corneal epithelial cells are known to be exposed to shear stresses caused by eyelids during blinking and eye rubbing [23], little is known about its effects on cell phenotype. Using an “ in vitro whole-eye perfusion” model, applying shear stress to the surface of rabbit corneas led to changes in corneal epithelial cell morphology and increased shedding rate [24]. Additionally, using a cone and plate model, rabbit corneal epithelial cells exposed to shear stress were found to have increased ATP release [25].…”