MMP13 and keratoconus: Moreover, the increased expression of MMP-1, MMP-3, MMP-7, MMP-9, MMP-13, IL-4, IL-5, IL-6, IL-8, IL-17, TNF-α, and TNF-β in the tears of KC patients indicates that inflammatory and subsequent tissue degenerative processes play a significant role in the thinning and weakening of corneal connective tissue, contributing to the progressive degeneration observed in KC corneal structure (Balasubramanian et al., 2012b; Jun et al., 2011; Marques et al., 2023; Nichani et al., 2023; Peyman et al., 2021; Taurone et al., 2021).