NOX4 and keratoconus: Next, we examined the expression of Nox-2, Nox-4, Nrf-2 and HO-1 in HKs in the 106 kPa, 34.88 kPa and 16.70 kPa groups treated with H2O2 by immunofluorescence staining to evaluate the levels of proteins associated with oxidative stress in HKs in the KC mechanical microenvironment after H2O2 treatment (Fig. 8).