Clinical features: Symptoms: decreased best-corrected vision. Signs: corneal epithelial cells invade and grow under the corneal flap. Possible causes: implantation of epithelial cells during surgery, poor-quality blade, improper repositioning of the flap or gap between stromal bed and flap. Complication: irregular astigmatism, flap melting. Treatment: re-elevating the flap and irrigation with scraping of the stromal bed as well as the flap undersurface.