| Wound healing is critical to all corneal surgical procedures. Corneal wound healing also contributions to the efficacy and safety of refractive surgical procedures such as photorefractive keratectomy (PRK) and laser in situ keratomeliusis (LASIK), since it is a major factor in over-correction, under-correction, stromal opacity, and other complications that either myopia or hyperopia.In last decade, many ophthalmologists have paid attention to the wound healing response to the corneal refractive surgery. It was first demonstrated in 1996 that the early disappearance of keratocytes that follows epithelial injury is mediated by apoptosis. Apoptosis is a programmed cell death and plays a major role in modulating many physiological and pathological processes and apoptosis is gentle involutional form cell death that occurs without the release of lysosomal enzymes or other intracellular components that could damage the surrounding tissues or cells. Subsequent studies have suggested that apoptosis is mediated by cytokines such as IL-1, Fas-L, BMP-2, BMP-4, TNF-a released from the injured epithelium and the magnitude of keratocyte apoptosis at 4 hr time point paralleled the level of keratocyte proliferation and myofibroblast density in stroma.The keratocyte apoptosis response is most commonly detected with the terminal-deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay and electron microscopy. Keratocyte apoptosis is detected within minutes of epithelial injury by electron microscopy. Conversely DNA fragmentation detected by the TUNEL assay takes longer to develop (10-30min) and has been found to be most prominent at approximately 4hr after scrape injury in mice and rabbits~[8,9] Keratocyte apoptosis is the first observable stromal change following epithelial injury. Following initiation of keratocyte apoptosis other cellular processes occur in stroma. Remaining keratocytes begin to proliferate and myofibroblasts may be generated~[10,11]. The complex cellular response contributes to stromal remolding and modulated healing of the overlying epithelial cells.At present, laser in situ keratomeliusis (LASIK)and phtorefrective keratectomy (PRK) have become the most popular surgical technique for correcting myopia and myopic astigmatism, whereas the effect of LAS IK and PRK was influenced with some factors, the most important factor was corneal wound healing. The present study included 50 rabbits that had PRK and LASIK (low or high ablation) for myopia with qualitative and quantitative study of apoptosis, Transmission electron microscopy (TEM) was performed to confirm apoptosis in stroma following PRK and LASIK. Through these methods to investigate the character of the keratocyte apoptosis at each particular time point after surgery and to discuss the correlation between the level of apoptosis and the type of surgery and the deepness of laser ablation.[Objective]The aim of this study was to investigate the character of the keratocyte apoptosis at each particular time point following PRK and LASIK and to discuss the correlation between the level of apoptosis and the type of surgery and the deepness of laser ablation.[Methods]A total of 50 12- to 15- week-old New Zealand white rabbits weighting 3.5 -4.0 Kg each were included in the data analysis in this study. The 50 rabbits were divided into 2 groups(A and B) at random. Twenty-five of these rabbits were operated with PRK and other twenty-five rabbits were operated with LASIK. Each rabbit was corrected -4.0diopters on left eyes and -8.0 diopters on right eyes.Anesthesia was obtained by intravenous injection of Pentobarbital Sodium (30mg/Kg). In addition .topical Oxybuprocaine 0.4% was applied to each eye just before surgery. Group A: With the animal under general and local anesthesia, a 7mm-diameter area of epithelium overly the pupil was removed by scraping with a blade. A laser ablation the corresponding sphere correction with a 6.0mm-diameter optical zone was performed and correction of -4.0D on left eye and correction of -8.0D on right eye. Group B: A... |
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