MMP9 and allergic disease: Importantly, biomarker-guided patient stratification is gaining traction—ocular surface inflammation has been implicated in KC progression [38]; a pathogenic triad comprising allergy, eye rubbing, and elevated IgE–MMP-9 levels has been proposed [39]; and MMP-9 positive allergic patients have been shown to be at increased risk of progression, as documented by Mazzotta et al. [11].