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

To investigate the role of acute inflammation in keratocyte death, which may influence corneal haze after photorefractive keratectomy (PRK).

Transepithelial PRK was performed on both eyes of 30 rabbits. Twenty-six rabbits were divided into 4 groups receiving autologous blood, suturing alone, suturing with amniotic membrane graft, or no treatment as the control. Twenty-four hours later, the ablated zone was analyzed for keratocyte death by TdT-dUTP terminal nick-end label (TUNEL) staining and transmission electron microscopy, for polymorphonuclear cell (PMN) infiltration by hematoxylin-eosin staining, and for oxygen radical-induced lipid peroxidation by malondialdehyde immunohistochemistry. The remaining four rabbits were subjected to PRK or mechanical scraping and analyzed immediately or after culturing for 24 hours.

Compared with the control group where TUNEL-positive keratocytes were found only in the superficial ablated stroma, blood application or suturing 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). There was a strong correlation between keratocyte death and PMN infiltration (P: < 0.01, correlation factor = 0.786). Transmission electron microscopy revealed that the majority of keratocyte death was due to necrosis. Amniotic membrane stroma trapped and prevented PMN infiltration into the stroma. Malondialdehyde-modified antigen was found on the ablated surface and around infiltrated PMN.

Transepithelial PRK causes oxygen radical-mediated lipid peroxidation on the superficial stroma and may contribute to superficial keratocyte death even in the absence of inflammation. Mechanical scraping leads to apoptosis without the participation of inflammation. Keratocyte death by necrosis spreads to the deeper part of the stroma and correlates with additional acute inflammation. Amniotic membrane precludes PMN infiltration and decreases 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.