By Joanna Lyford, Senior medwireNews Reporter
Rubbing the eyes leads to an increase in protease activity and levels of protease and inflammatory mediators, a clinical study shows.
Noting that eye rubbing is the only known risk factor for keratoconus, the study authors speculate that persistent and forceful eye rubbing may drive the development or progression of the disease.
"Upregulated proteases and inflammatory molecules may be causal links between eye rubbing and keratoconus," write Sivaraman Balasubramanian (The University of New South Wales, Kensington, Australia) and co-authors in Clinical and Experimental Optometry.
Keratoconus is a progressive, debilitating ocular disease that is linked to abnormal or forceful eye rubbing, often with a characteristic circular motion that exerts pressure localized to the cornea.
In this study, Balasubramanian et al analyzed levels of proteolytic enzymes and inflammatory mediators in tears before and after rubbing in 17 healthy individuals.
Results showed that eye rubbing for 60 seconds led to a significant increase in tear levels of matrix metalloproteinase-13 (from 51.9 to 63.0 pg/mL), interleukin-6 (from 1.24 to 2.02 pg/mL), and tumor necrosis factor-α (from 1.16 to 1.44 pg/mL).
Eye rubbing did not alter collagenase activity or total protein levels, however.
The researchers hypothesize that the changes in tear composition induced by eye rubbing could be due to the mechanical effects of rubbing the upper palpebral conjunctiva against the corneal surface and bulbar conjunctiva.
"These proteases and inflammatory molecules have the potential to induce apoptosis of the keratocytes, which is the major form of cell death in keratoconic corneas," they remark.
Furthermore, persistent eye rubbing might cause a greater increase in the levels and activity of these molecules, with the potential to contribute to the development or progression of the disease.
The researchers conclude: "Elucidating the factors responsible for the habit of abnormal chronic central eye rubbing in some patients with keratoconus could help in the management of rubbing habits and in understanding the etiology of the disease."
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