MMP9 and dry eye syndrome: Indeed, increased levels of pro-inflammatory cytokines such as interleukin 1 (IL-1), IL-6, and tumor necrosis factor-α (TNF-α), chemokines such as IL-8 and monocyte chemotactic protein-1 (MCP-1), and matrix metalloproteinase-9 (MMP-9) have been demonstrated to be associated with ocular surface diseases [1,4,18,19] including dry eye [20,21].