MMP1 and corneal ulcer: Polyinosinic-polycytidylic acid, a synthetic analog of viral double-stranded RNA, induced the expression and secretion of MMP-1 and MMP-3 by cultured human corneal fibroblasts; expression of MMPs by corneal fibroblasts could be responsible for collagen degradation in the corneal stroma, leading to corneal ulceration and perforation after viral infection126