F. oxysporum invasion into human corneas incubated at pH 7.3 (periodic acid-Schiff; original magnification, ×200). A, Wild-type fungi invaded the superficial corneal surface within one day. B, The wild-type strain progressed into the deeper corneal stroma by the third day following inoculation. C, The loss-of-function mutant pacC+/-12 produced no fungal hyphae within corneal tissue on day 1. D, On the third day after inoculation the F. oxysporum pacC+/-12 mutant produced hyphae that invaded into the anterior stroma. E, The dominant-activating strain pacCc9 formed hyphae in the superficial stroma on day 1. F, The pacCc9 strain proliferated on the corneal surface and continued to extend into the corneal stroma on day 3.