MMP1 and corneal ulcer: Corneal fibroblasts (activated keratocytes) produce MMPs in response to certain stimuli [11,12], with collagenase (MMP-1), stromelysin (MMP-3), and gelatinase (MMP-2) enzymes having been shown to be secreted by these cells in response to stimuli associated with corneal ulceration [13-17].