Cell Biology of Spontaneous Persistent Epithelial Defects After Photorefractive Keratectomy in Rabbits

PURPOSE: To evaluate wound healing in rabbit corneas that developed a spontaneous persistent epithelial defect (PED) after photorefractive keratectomy (PRK). METHODS: Forty-eight 10- to 15-week-old female New Zealand White rabbits weighing 2.5 to 3.0 kg underwent either –3 diopter (D) or –9 D PRK to generate a series of corneas to study wound healing after injury. During that series, seven corneas developed a PED detected with 1% fluorescein staining at a slit lamp that either did not have epithelial closure by 1 week after surgery or subsequently had the closed epithelium break down to form a PED 2 to 3 weeks after surgery. The corneas had slit-lamp photography, with and without 1% fluorescein, and were removed from the normal PRK series. Each PED cornea was evaluated using immunohistochemistry for the myofibroblast marker α–smooth muscle actin (α-SMA), keratocyte marker keratocan, and mesenchymal cell marker vimentin, as well as basement membrane components perlecan and collagen type IV. RESULTS: All seven corneas that had PRK with a PED, even the two evaluated at only 1 week after PRK, had α-SMA–positive myofibroblasts populating the anterior stroma within the PED, along with comingled α-SMA–negative cells that were likely corneal fibroblasts and possibly bone marrow–derived fibrocytes. Both perlecan and collagen type IV accumulated in the anterior stroma of the epithelial defects without an epithelial basement membrane, likely produced by corneal fibroblasts to modulate transforming growth factor–β entering the stroma from the tears and peripheral epithelium. CONCLUSIONS: Corneas with a PED that occurred following PRK (a procedure that produces a transient neurotropic state in the cornea) had myofibroblasts populating the superficial stroma within the epithelial defect as early as 1 week after the surgery. TRANSLATIONAL RELEVANCE: Pharmacologic treatments that trigger myofibroblast apoptosis, including topical losartan, could facilitate decreased scarring fibrosis in corneas with a PED.