Modulation of acute inflammation and keratocyte death by suturing, blood, and amniotic membrane in PRK

PURPOSE. To investigate the role of acute inflammation in keratocyte death, which may influence corneal haze after photorefractive kerarectomy (PRK). METHODS. Transepithelial PRIG was performed on both eyes of 30 rabbits. Twe nty-six rabbits were divided into 4 groups receiving autologous blood, sutu ring alone, suturing with amniotic membrane graft, or no treatment as the c ontrol. Twenty-four hours later, the ablated zone was analyzed for keratocy te death by TdT-dUTP terminal nick-end label (TUNEL) staining and transmiss ion electron microscopy, for polymorphonuclear cell (PMN) infiltration by h ematoxylin-eosin staining, and for oxygen radical-induced lipid peroxidatio n by malondialdehyde immunohistochemistry. The remaining four rabbits were subjected to PRK or mechanical scraping and analyzed immediately or after c ulturing for 24 hours. RESULTS. Compared with the control group where TUNEL-positive keratocytes w ere found only in the superficial ablated stroma, blood application or sutu ring caused more and deeper keratocyte death and PMN infiltration (P < 0.05 ). The amniotic membrane graft group had less keratocyte death and PMN than the control or the suture group (P < 0.05 and P < 0.01, respectively). The re was a strong correlation between keratocyte death and PMN infiltration ( P < 0.01, correlation factor = 0.786). Transmission electron microscopy rev ealed that the majority of keratocyte death was due to necrosis. Amniotic m embrane stroma trapped and prevented PMN infiltration into the stroma. Malo ndialdehyde-modified antigen was found on the ablated surface and around in filtrated PMN. CONCLUSIONS. Transepithelial PRK causes oxygen radical-mediated lipid perox idation on the superficial stroma and may contribute to superficial keratoc yte death even in the absence of inflammation. Mechanical scraping leads to apoptosis without the participation of inflammation. Keratocyte death by n ecrosis spreads to the deeper part of the stroma and correlates with additi onal acute inflammation. Amniotic membrane precludes PMN infiltration and d ecreases lipid peroxidation and keratocyte death. Future studies are needed to discern whether prevention of inflammation-mediated keratocyte necrosis can reduce unwanted scarring caused by PRK.