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Objectives: (1) To explore the role and significance of Matrix Metalloproteinase 9 (MMP-9), a proteolytic enzyme, in various ocular surface diseases of inflammatory, infectious, and traumatic etiology (2), to further elucidate the molecular mechanisms responsible for its overexpression in ocular surface disease states, and (3) to discuss possible targets of therapeutic intervention. Methods: A literature review was conducted of primary sources from 1995 onward using search results populated from the US National Library of Medicine search database. Results: MMP-9 overexpression has been found in in vitro and in vivo models of dry eye disease (DED), corneal ulceration, microbial keratitis, corneal neovascularization, ultraviolet light-induced radiation, and a host of additional surface pathologies. MMP-9 is involved in an intricate signal transduction cascade that includes induction by many proinflammatory molecules including interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-a), nuclear factor kappa light chain enhancer of activated B cells (NF-kB), platelet-activating factor, activator protein 1 (AP-1), and transforming growth factor beta (TGF-B). MMP-9 expression is blunted by a diverse array of molecular factors, such as tissue inhibitors of metalloproteinases, cyclosporine A (CyA), PES_103, epigalloccatechin-3-gallate (EGCG), N-acetylcysteine (NaC), ascorbate, tetracyclines, and corticosteroids. Inhibition of MMP-9 frequently led to improvement of ocular surface disease. Conclusions: Novel insights into the mechanistic action of MMP-9 provide potential for new therapeutic modulations of ocular surface diseases mediated by its overexpression.