Background/Aims: Tissue degradation in corneal thinning disorders, such as keratoconus (KC), involves the expression of inflammatory mediators. The purpose of this study was to determine the levels of proinflammatory cytokines and matrix metalloproteinase 9 (MMP-9) in tears from both eyes of unilateral keratoconus (KC) patients.
Methods: Thirty patients diagnosed with asymmetric KC (30 KC eyes, and 30 subclinical KC eyes) and 20 normal control subjects (1 eye) were studied in a prospective, cross sectional study.
Keratoconus screening programs were performed on these participants. Ten microliters of tears were collected from each eye. The concentrations of cytokines (interleukin-6 [IL-6] and tumor necrosis factor α [TNF-α]), and MMP-9 were measured by ELISA.
Results: Mean values for IL-6 levels were similar in KC and subclinical KC samples (5.5 [4.9 - 6.9] vs. 5.7 [4.5 - 6.2] pg/mL, p= 0.131), but significantly higher in relation to the control group (2.2 [1.0 - 4.1] pg/ml, p<0.0001). Significant differences were found in TNF-α levels between KC and subclinical KC eyes (5.4 [4.1 - 6.8] vs. 4.8 [4.2 - 6.0] pg/mL, p= 0.032) and control group (1.8 [1.5 - 2.3] pg/mL, p<0.0001). Increased values of MMP-9 were found in KC (59.4 [50.6-66.1] ng/mL) vs. subclinical KC eye (7.0 [4.8-8.6] ng/mL) (p<0.0001). MMP-9 levels in the control group (6.1 [3.9 - 8.3] ng/mL) and subclinical KC were similar (p= 0.203).
Conclusions: IL-6 and TNF-α are overexpressed in the tears of subclinical and KC eyes. Increased MMP-9 levels were found only in the KC eye. These results indicate that the pathogenesis of KC may involve chronic inflammatory events.