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. This evidence concerns the gene MMP3 and corneal ulcer.