MMP9 and keratoconus: Another study reports elevated levels of estradiol in the plasma of men with keratoconus with respect to the control population, which could be related to the increase in proinflammatory cytokines (IL-6, IL-1β, IL-8 and GM-CSF) and in the activity of MMP-2 and MMP-9 involved in the etiology of keratoconus.