MMP9 and keratoconus: Studies conducted by Sobrino et al. showed an increased expression of toll-like receptors (TLRs), in particular TLR2 and TLR4, in the blood of patients with keratoconus, which was associated with increased levels of inflammatory mediators in serum, such as nuclear transcription factor NF-kB, IL-6, IL-1B, TNF-α, and MMP-9 [16].