Effects of eye rubbing on the levels of protease, protease activity and cytokines in tears: relevance in keratoconus

Background Proteases, protease activity and inflammatory molecules in tears have been found to be relevant in the pathogenesis of keratoconus. We sought to determine the influence of eye rubbing on protease expression, protease activity and concentration of inflammatory molecules in tears. Methods Basal tears were collected from normal volunteers before and after 60 seconds of experimental eye rubbing. The total amount of matrix metalloproteinase (MMP)-13 and inflammatory molecules interleukin (IL)-6 and tumour necrosis factor (TNF)- in the tear samples were measured using specific enzyme-linked immunosorbent assays (ELISA). Tear collagenase activity was investigated using a specific activity assay. Results The concentrations of MMP-13 (51.9 +/- 34.3 versus 63 +/- 36.8pg/ml, p = 0.006), IL-6 (1.24 +/- 0.98 versus 2.02 +/- 1.52pg/ml, p = 0.004) and TNF- (1.16 +/- 0.74 versus 1.44 +/- 0.66pg/ml, p = 0.003) were significantly increased in normal subjects after eye rubbing. The experimental eye rub did not alter significantly the collagenase activity (5.02 +/- 3 versus 7.50 +/- 3.90 fluorescent intensity units, p = 0.14) of tears. Conclusion Eye rubbing for 60 seconds increased the level of tear MMP-13, IL-6 and TNF- in normal study subjects. This increase in protease, protease activity and inflammatory mediators in tears after eye rubbing may be exacerbated even further during persistent and forceful eye rubbing seen in people with keratoconus and this in turn may contribute to the progression of the disease.