Scarring trachoma is associated with increased expression of MMP9 and a coding SNP that is adjacent to the active binding site of the MMP9 enzyme [46,68,91], and with differential expression of MMPs 7, 9, 10 and 12 and tissue inhibitor of MMP (TIMP)-1; recurrence of trichiasis after surgery is associated with an altered MMP1/TIMP1 transcript ratio [55,67,68,92]. This evidence concerns the gene MMP9 and Trichiasis.