TNF and keratoconus: Values below the LLOQ were observed rarely: 12.5% (n = 6, three in each group) for IFN-γ, 4.17% (n = 2, both in the keratoconus group) for IL-17A, 2.08% (n = 1 in the control group) for TNF-α and never for the remaining cytokines.