HISTOLOGICAL, IMMUNOHISTOCHEMICAL, AND ULTRASTRUCTURAL FINDINGS IN HUMAN CORNEAS AFTER PHOTOREFRACTIVE KERATECTOMY

BACKGROUND: Four human corneas that had undergone photorefractive kera tectomy (PRK) and subsequent penetrating keratoplasty were examined by means of light and electron microscopy in an attempt to detect possib le causes for complications after PRK. METHODS: Four eyes with a centr al corneal leukoma resulting from a previous PRK treatment underwent p enetrating keratoplasty respectively 3 days, 3 months, 5 months, and 1 3 months after the refractive procedure. Different excimer laser instr uments (Meditec MEL 50, Summit UV200, and VISX 20/20) had been used. T he corneal buttons removed were submitted for light microscopy, electr on microscopy and immunohistochemistry. RESULTS: An immature (one to t wo layers, basement membrane anomalies) but continuous epithelium was present even in the 3-day specimen; between six and eight epithelial l ayers could be seen in the 13-month specimen, which still presented an undulated aspect of the otherwise normal basement membrane. A continu ous acellular collagen layer underlying the epithelium of the ablated area was detected in the superficial stroma of all examined corneas. N o Descemet's membrane or endothelial alterations could be seen. CONCLU SIONS: Despite recovery of a continuous epithelial layer as early as 3 days after PRK, abnormalities of both epithelium and superficial stro ma could be detected in all specimens, including the one obtained 13 m onths after the refractive procedure.