MMP9 and keratoconus: Elevated levels of interleukin- (IL-) 1b, IL-4, IL-5, IL-6, IL-8, and IL-17; tumor necrosis factor (TNF)-α, -β; interferon- (IFN-) γ; matrix metalloproteinase- (MMP-) 1, MMP-3, MMP-7, MMP-9, and MMP-13; Cathepsin B; and Lipocalin-1 have been found in the tears of patients with keratoconus [4–11].