Epithelial Responses to Rubbing-Related Mechanical Forces

Abstract

To examine for epithelial thickness changes in response to compressive and shear forces associated with eye rubbing. The Holden-Payor optical pachometer was used to measure total and stromal-endothelial thickness, at central (right eye) and midperipheral (left eye) locations, for 12 subjects with normal corneas. Epithelial thickness was determined by subtraction. Baseline measurements were compared with measurements recorded immediately after 15 seconds of circular pattern rubbing over the cornea, using an index finger pad, and light to moderate force. Four subjects in each of 3 groups with mean ages of 19.5, 45.3, and 70.2 years were assessed. Measurement continued at 15-minute intervals until baseline thickness was restored. An 18.4% reduction in epithelial thickness was recorded immediately after rubbing for central right eye and midperipheral left eye assessments. Both findings were statistically significant (P < 0.05). Recovery to baseline thickness occurred between 15 and 30 minutes centrally and between 30 and 45 minutes midperipherally. These results indicate a statistically significant mechanical trauma to the epithelium after 15 seconds of light to moderate rubbing. With reference to the rheological properties of the cytoskeleton, an attempt to explain how the epithelium could lose and recover thickness has been made. Apart from cell flattening, displacement from the rubbed area of intercellular water, cytoplasm from ruptured cells, chains of wing cells, and mucin are suggested as possible thinning mechanisms. Extraneous eye rubbing may adversely alter the results obtained with pachymetry, videokeratography, wavefront aberrometry, refraction, and results obtained with orthokeratology contact lenses.