Immunohistochemical localization of EGF, TGF-alpha, TGF-beta, and their receptors in rat corneas during healing of excimer laser ablation

PURPOSE: Members of the epidermal growth factor (EGF) and transforming growth factor beta (TGF-beta) families of growth factors and receptors are known to regulate key aspects of corneal wound healing, including epithelial migration and scar formation. To further understand their roles, mRNA levels were measured and proteins were immunolocalized in rat corneas at multiple time points during healing of excimer laser ablation injury. METHODS: Excimer laser photoablation was performed to a depth of 50 microm on rat corneas. Levels of mRNAs for EGF, TGF-alpha, TGF-beta isoforms 1, 2, and 3, and their receptors (EGF-R and TGFbeta-IIR) were measured by quantitative RT-PCR on days 0, 1.5, 7, 21, 42, and 91 after ablation. Immunohistochemical localization of the growth factors and their receptors was performed on days 0, 7, and 21 in corneal sections. RESULTS: Levels of EGF mRNA remained stable in rat corneas after ablation (68 +/- 12 copies/cell, mean +/- SD), whereas levels of TGF-alpha mRNA progressively increased sixfold to a maximum at day 42 (300 copies/cell) then slightly decreased on day 91. Levels of EGF-R mRNA rapidly increased 60-fold on day 7 compared with day 0 (571 vs. 9 copies/cell) then decreased sixfold above baseline at day 91. Levels of TGF-beta1 mRNA remained stable (36 +/- 10 copies/cell), whereas levels of TGF-beta2 and TGF-beta3 mRNAs peaked on day 21 (300-fold and 25-fold increase) and remained elevated through day 91. Levels of TGFbeta-IIR mRNA showed a similar pattern. Immunostaining of all the growth factors and receptors was primarily in basal layers of epithelial cells in uninjured cornea and during healing. Intensity of immunostaining for TGF-beta1, TGFbeta-IR, and TGFbeta-IIR increased appreciably in the basal epithelial layers after ablation. CONCLUSIONS: Levels of mRNAs for several key members of the EGF and TGF-beta systems increase during corneal wound healing. In addition, the proteins are primarily localized in basal layers of epithelial cells, which suggest these cells are active in synthesizing autocrine and paracrine growth factors that modulate corneal wound healing.     

Connective tissue growth factor expression and action in human corneal fibroblast cultures and rat corneas after photorefractive keratectomy

PURPOSE: Connective tissue growth factor (CTGF) has been linked to fibrosis in several tissues. In this study, the interactions between CTGF and transforming growth factor (TGF)-beta were assessed in human corneal fibroblasts, and the levels and location of CTGF protein and mRNA were measured during healing of excimer laser ablation wounds in rat corneas. METHODS: Human corneal fibroblasts were incubated with TGF-beta1, -beta2, and -beta3 isoforms, and CTGF mRNA and protein were measured. CTGF was immunolocalized in the cultured fibroblasts by using a specific antibody. Regulation of collagen synthesis by TGF-beta and CTGF was assessed in human corneal fibroblasts with a neutralizing antibody and an antisense oligonucleotide to CTGF. CTGF mRNA and protein were measured in rat corneas up to day 21 after excimer ablation of the cornea. CTGF protein was immunolocalized in rat corneas after photorefractive keratectomy (PRK), and the presence of CTGF mRNA and protein in ex vivo rat corneal scrapings was established. RESULTS: All three TGF-beta isoforms stimulated expression of CTGF in human corneal fibroblasts, and CTGF was immunolocalized in the cells. Both TGF-beta and CTGF increased collagen synthesis in corneal fibroblasts. Furthermore, CTGF antibody or antisense oligonucleotide blocked TGF-beta-stimulated collagen synthesis. CTGF protein and mRNA increased in rat corneas through day 21 after PRK. CTGF expression was also detected in ex vivo scrapings of rat corneas. CONCLUSIONS: These data demonstrate that CTGF is expressed by corneal cells after stimulation by TGF-beta, that CTGF expression increases significantly during corneal wound healing, and that CTGF mediates the effects of TGF-beta induction of collagen synthesis by corneal fibroblasts. These data support the hypothesis that CTGF promotes corneal scar formation and imply that regulating CTGF synthesis and action may be an important goal for reducing corneal scarring.     

Relation between corneal haze and transforming growth factor-beta1 after photorefractive keratectomy and laser in situ keratomileusis.

PURPOSE: To investigate the relation between corneal haze formation and transforming growth factor-beta (TGF-beta) after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, University of Tokyo Graduate School of Medicine, Tokyo, Japan. METHODS: White rabbits were divided into 4 groups, with each group receiving 1 of the following surgeries: manual epithelial abrasion, PRK, lamellar keratotomy, or LASIK. The degree of corneal haze was quantitatively analyzed by measuring the light scattering intensity of corneas before and 4 and 12 weeks after surgery. The expression of type IV collagen and TGF-beta1 in the corneas at baseline and at 4 weeks was examined immunohistochemically. RESULTS: The light scattering intensity was significantly greater 4 and 10 weeks after PRK. In contrast, epithelial abrasion, lamellar keratotomy, and LASIK did not influence the light scattering intensity of the corneas. Type IV collagen was detected in the basal lamina of the corneal epithelium and in Descement's membrane in the normal cornea. After epithelial abrasion, there was no change in the distribution of type IV collagen. Four weeks after PRK, the expression of type IV collagen was detected in the subepithelial layer of the laser-ablated area. Four weeks after lamellar keratotomy, type IV collagen was linearly and fragmentarily detected in the corneal stroma. Four weeks after LASIK, type IV collagen was linearly and continuously detected in the corneal stroma and was detected slightly in the subepithelial region of the laser-ablated area. In the normal corneas, the expression of TGF-beta1 was not detected in the keratocytes. Four weeks after PRK, the expression of TGF-beta1 increased in the keratocytes that proliferated in the subepithelial fibrous layer. In contrast, epithelial abrasion, lamellar keratotomy, and LASIK did not change the expression pattern of TGF-beta1 in the keratocytes. CONCLUSION: The multiplier effect of epithelial abrasion and excimer laser ablation in PRK may increase the expression of TGF-beta1 in keratocytes and induce corneal haze.     

Effect of anti-inflammatory agents on corneal wound-healing process after surface excimer laser keratectomy

PURPOSE: To investigate the effect of anti-inflammatory agents on conjunctival inflammation and corneal haze formation after excimer laser keratectomy. SETTING: Department of Ophthalmology, University of Tokyo Faculty of Medicine, Tokyo, Japan. METHODS: After excimer laser keratectomy was performed in 21 rabbits (42 eyes), saline, betamethasone 0.1%, or diclofenac 0.1% was topically applied 6 times a day for 4 weeks and then 3 times a day for 8 weeks. The degree of conjunctival inflammation was determined 1, 2, 3, and 7 days after the keratectomy. The degree of corneal haze was quantitatively measured using a digital analyzer before and once a week after the keratectomy. The expression of type IV collagen in the corneas at baseline and 4 and 12 weeks after the keratectomy was examined immunohistochemically. RESULTS: Compared with saline, betamethasone and diclofenac significantly decreased early-phase conjunctival inflammation. Betamethasone significantly inhibited corneal haze formation compared with saline at 3 to 5 and 8 to 12 weeks. Diclofenac did not inhibit corneal haze formation significantly. Although betamethasone tended to be more effective in inhibiting corneal haze formation and deposition of type IV collagen than diclofenac, there was no statistical difference between the 2 anti-inflammatory agents. CONCLUSION: Topically applied betamethasone effectively suppressed corneal haze formation after excimer laser keratectomy. Diclofenac was not statistically effective in inhibiting corneal haze formation.     

准分子激光屈光性角膜切削术后兔眼角膜组织细胞外基质成分的变化

目的 动态观察准分子激光屈光性角膜切削术（photorefractive keratectomy,PRK) 后角膜组织细胞外基质（extracellular matrix,ECM)成分的变化,并探讨其与角膜雾状混浊（haze）的关系。方法 24只兔按术后即刻、24h、1周、2周、1个月、3个月、6个月及12个月不同处死时间分为8个实验组,每组3只,按设计矫正度数－10．00D行右眼PRK术,术后裂隙灯显微镜检查各组角膜的haze分级,并取角膜组织以及免疫组织化学方法检测ECM成分,包括Ⅰ型胶原蛋白、Ⅲ型胶原蛋白、Ⅳ型胶原蛋白、细胞纤维连接蛋白（cellular fibronectin,cFN)、细胞黏合素（tenascin,TN)以层黏连蛋白（laminin,LN)。结果 PRK术后haze的发生率为100％;角膜基质浅层内沉积新合成的Ⅰ、Ⅲ、Ⅳ型胶原蛋白及cFN、TN、LN等ECM成分,其表达量变化与haze分级变化基本一致。结论 PRK术后切削区角膜基质浅层ECM成分的沉积与角膜haze的出现密切相关。     

Biomechanical and wound healing characteristics of corneas after excimer laser keratorefractive surgery: is there a difference between advanced surface ablation and sub-Bowman's keratomileusis?

PURPOSE: To describe the biomechanical and wound healing characteristics of corneas after excimer laser keratorefractive surgery. METHODS: Histologic, ultrastructural, and cohesive tensile strength evaluations were performed on 25 normal human corneal specimens, 206 uncomplicated LASIK specimens, 17 uncomplicated sub-Bowman's keratomileusis (SBK) specimens, 4 uncomplicated photorefractive keratectomy (PRK) specimens, 2 uncomplicated advanced surface ablation (ASA) specimens, 5 keratoconus specimens, 12 postoperative LASIK ectasia specimens, and 1 postoperative PRK ectasia specimen and compared to previously published studies. RESULTS: Histologic and ultrastructural studies of normal corneas showed significant differences in the direction of collagen fibrils and/or the degree of lamellar interweaving in Bowman's layer, the anterior third of the corneal stroma, the posterior two-thirds of the corneal stroma, and Descemet's membrane. Cohesive tensile strength testing directly supported these morphologic findings as the stronger, more rigid regions of the cornea were located anteriorly and peripherally. This suggests that PRK and ASA, and secondarily SBK, should be biomechanically safer than conventional LASIK with regard to risk for causing keratectasia after surgery. Because adult human corneal stromal wounds heal slowly and incompletely, all excimer laser keratorefractive surgical techniques still have some distinct disadvantages due to inadequate reparative wound healing. Despite reducing some of the risk for corneal haze compared to conventional PRK, ASA cases still can develop corneal haze or breakthrough haze from the hypercellular fibrotic stromal scarring. In contrast, similar to conventional LASIK, SBK still has the short- and long-term potential for interface wound complications from the hypocellular primitive stromal scar. CONCLUSIONS: Ophthalmic pathology and basic science research show that SBK and ASA are improvements in excimer laser keratorefractive surgery compared to conventional LASIK or PRK, particularly with regard to maintaining corneal biomechanics and perhaps moderately reducing the risk of corneal haze. However, most of the disadvantages caused by wound healing issues remain.     

Plasminogen activator activity and inhibition in rabbit tears after photorefractive keratectomy

Plasminogen activator is a normal component of tear fluid that plays a role in corneal wound healing processes. This work examines whether inhibitor-induced low levels of plasminogen activator activity (PAA) during corneal re-epithelialization after excimer laser photorefractive keratectomy (PRK) correlates with the eventual occurrence of haze in rabbit eyes. Tear samples were collected with glass capillaries from 16 eyes of eight New Zealand rabbits, using i.m. injection of pilocarpine hydrochloride for stimulation. Tears were collected before and after PRK surgery, and then daily for 5 days, and every fourth day thereafter for 3 months. Both eyes underwent PRK treatment. One eye of each rabbit was treated as a control while the contralateral eye was treated with aprotinin, a serine protease inhibitor, over the first 7 days. PAA in the tear samples was measured by a spectrophotometric method using human plasminogen and chromogenic peptide substrate S-2251. For the eight control eyes after PRK, the PAA values were significantly lower (day 1) and higher (days 2 and 3) than the equilibrium PAA (p<0.001). The corneas remained clear in each of these control eyes. For the eight contralateral aprotinin-treated eyes after PRK, the PAA values on days 1-7 were significantly lower than the equilibrium PAA (p<0.001). All eight of these aprotinin-treated eyes developed corneal haze after 2 months. There was no significant difference (p=0.06) between control and aprotinin-treated eyes for the equilibrium PAA after 19 days. We conclude that a corneal wound healing abnormality (haze) develops in rabbit eyes after PRK when PAA levels are reduced using aprotinin for a week following PRK.     

Stromal haze, myofibroblasts, and surface irregularity after PRK

The aim of this study was to investigate the relationship between the level of stromal surface irregularity after photorefractive keratectomy (PRK) and myofibroblast generation along with the development of corneal haze. Variable levels of stromal surface irregularity were generated in rabbit corneas by positioning a fine mesh screen in the path of excimer laser during ablation for a variable percentage of the terminal pulses of the treatment for myopia that does not otherwise generate significant opacity. Ninety-six rabbits were divided into eight groups: [see table in text]. Slit lamp analysis and haze grading were performed in all groups. Rabbits were sacrificed at 4 hr or 4 weeks after surgery and histochemical analysis was performed on corneas for apoptosis (TUNEL assay), myofibroblast marker alpha-smooth muscle actin (SMA), and integrin alpha4 to delineate the epithelial basement membrane. Slit-lamp grading revealed severe haze formation in corneas in groups IV and VI, with significantly less haze in groups II, III, and VII and insignificant haze compared with the unwounded control in groups I and V. Analysis of SMA staining at 4 weeks after surgery, the approximate peak of haze formation in rabbits, revealed low myofibroblast formation in group I (1.2+/-0.2 cells/400x field) and group V (1.8+/-0.4), with significantly more in groups II (3.5+/-1.8), III (6.8+/-1.6), VII (7.9+/-3.8), IV (12.4+/-4.2) and VI (14.6+/-5.1). The screened groups were significantly different from each other (p < 0.05), with myofibroblast generation increasing with higher surface irregularity in the -4.5 diopter PRK groups. The -9.0 diopter PRK group VI had significantly more myofibroblast generation than the -9.0 diopter PRK with PTK-smoothing group VII (p < 0.01). Areas of basement membrane disruption were demonstrated by staining corneas for integrin alpha4 and were prominent in corneas with grade I or higher haze. SMA-positive myofibroblasts tended to be present sub-adjacent to basement membrane defects. Late apoptosis was detected at 1 month after surgery within clusters of myofibroblasts in the sub-epithelial stroma. In conclusion, these results demonstrated a relationship between the level of corneal haze formation after PRK and the level of stromal surface irregularity. PTK-smoothing with methylcellulose was an effective method to reduce stromal surface irregularity and decreased both haze and associated myofibroblast density. We hypothesize that stromal surface irregularity after PRK for high myopia results in defective basement membrane regeneration and increased epithelium-derived TGFbeta signalling to the stroma that increases myofibroblast generation. Late apoptosis appears to have a role in the disappearance of myofibroblasts and haze over time.     

Plasminogen activator activity in tears after excimer laser photorefractive keratectomy

PURPOSE: To quantify changes of plasminogen activator activity in tear fluid during corneal re-epithelialization after excimer laser photorefractive keratectomy (PRK). METHODS: Tear samples were collected with glass capillaries from 77 eyes of 42 patients immediately before and immediately after PRK treatment and on postoperative days 3 and 5. In 20 patients, the contralateral eye was similarly sampled to serve as control. Plasminogen activator activity in the tear samples was measured by a spectrophotometric method using human plasminogen and chromogenic peptide substrate, D-valyl-L-leucyl-L-lysine-p-nitroanilide (S-2251). RESULTS: In tears of all eyes that underwent PRK, the plasminogen activator activities were lower immediately after PRK than were the preoperative values. For patient eyes with normal wound healing, tear plasminogen activator activities were significantly elevated above the preoperative level on the third postoperative day and then returned to the preoperative level by the fifth postoperative day. In contrast, tear plasminogen activator activities remained low through the third postoperative day in all (six) eyes in which haze developed after 3 to 6 months. The contralateral control eyes showed no appreciable change in plasminogen activator activity over the 5-day period. CONCLUSIONS: Plasminogen activator activity levels measured in tears of excimer laser PRK-treated eyes may serve as a predictor of wound healing. Extended low levels of plasminogen activator activity through the third postoperative day correlate with the development of corneal healing abnormalities (haze). The low plasminogen activator activity could be not only an accompanying sign but also a cause of defective corneal wound healing.     

准分子激光角膜切削术与准分子激光原位角膜磨镶术角膜创口愈合的对比实验研究

比较准分子激光角膜切削术(photorefractive keratectomy,PRK)与准分子激光原位角膜磨镶术(1aser in situ keratomileusis,LASIK)后激光对角膜组织的切削效应及角膜的愈合情况,从组织学角度探讨角膜雾状混浊(Haze)及屈光度数回退的成因。方法24只新西兰白兔按预矫屈光度数随机分为-4.00 D组和-8.00 D组,每只兔右眼行PRK,左眼行LASIK。术后10d,1、3及6个月观察Haze情况并验光,每组随机处死3只兔取角膜行光镜、电镜及免疫组化检查,检测胶原Ⅲ、胶原Ⅳ、纤维连结蛋白(fibronectine,FN)及转化生长因子-β(transforming growth factor-β1,TGF-β2)的含量。结果行PRK术的右眼术后出现不同程度的Haze及屈光度数回退,其程度与预矫正屈光度数成正比。行LASIK术的左眼术后除少数角膜瓣周围半环形混浊外,手术区域角膜透明,屈光度数回退较右眼轻。-4.00 D组右眼与左眼术后屈光度数均稳定,-8.00 D组右眼较左眼屈光度数回退明显。右眼术后角膜愈合反应重,恢复慢。6个月时角膜基质仍处于修复阶段。左眼术后除形成角膜上皮栓及对应处基质轻度增生外,手术区域角膜瓣与基质床间界面清晰,无明显增生,角膜基质愈合反应轻、恢复快。术后所有兔眼角膜均有TGF-β1表达及活化,持续时间与角膜愈合时间一致。Haze及屈光度数回退组织学改变为：角膜上皮细胞增生,基底膜不成熟,前基质角膜细胞活化、增殖,新生胶原Ⅲ合成、排列紊乱,细胞外基质FN在角膜上皮下沉积。结论LASIK矫正近视尤其是高度近视优于PRK;角膜伤口愈合特别是基质愈合的反应程度,是。Haze及屈光度数回退的关键;TGF-β1是角膜愈合过程中重要调节因子,可通过介导角膜上皮一基质相互作用,调节胶原Ⅲ及FN的含量,参与瘢痕形成。     

Corneal haze after photorefractive keratectomy for myopia: role of collagen IV mRNA typing as a predictor of haze

PURPOSE: To develop a test based on the individual expression of collagen type IV synthesis in corneal epithelial cells to identify patients who have the potential for significant corneal haze after myopic photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology and the Institute of Microbiology, University of Regensburg, Germany. METHODS: The individual synthesis of collagen type IV alpha3 mRNA was quantitatively measured in corneal epithelial cells of 34 eye (34 patients) with myopia ranging from -1.5 to -10.0 diopters (D) by a polymerase chain reaction (PCR) test. The corneal epithelial cells were collected before the PRK procedure. Collagen type IV alpha3 mRNA levels were correlated to postoperative haze and regression at 12 months. RESULTS: In all samples, collagen type IV alpha3 mRNA was detected; the mean was 1.47 (range 0.11 to 6.42). There was a correlation between haze and the amount of collagen type IV alpha3 mRNA; that is, eyes with haze had more collagen IV expression. In contrast, no correlation was observed between regression and the amount of collagen type IV alpha3 mRNA. CONCLUSIONS: The results show that collagen type IV alpha3 is an important factor in the development of corneal haze after PRK. Based on a quantitative PCR test, the individual collagen IV mRNA concentration in corneal epithelial cells could be measured. Further development could establish a screening test by which eyes with pronounced synthesis of collagen IV could be identified as being at high risk for haze after PRK.     

Intact corneal epithelium is essential for the prevention of stromal haze after laser assisted in situ keratomileusis

AIMS: To determine the effect of intact corneal epithelium on stromal haze and myofibroblast cell formation after excimer laser surgery. METHODS: Denuded epithelium alone, photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), or LASIK with denuded epithelium was performed in rabbit eyes. Postoperative anterior stromal haze was assessed employing a standard scale. Immunohistochemical methods were used to detect alpha smooth muscle actin (alpha-SMA), a marker for myofibroblastic cells, and type III collagen in subepithelial corneal tissue. RESULTS: Three weeks after surgery, the presence of alpha-SMA positive long extended and spindle-shaped stromal cells, and synthesis of type III collagen were observed in the subepithelial stromal layer corresponding to corneal haze in PRK and LASIK with denuded epithelium, but not in denuded epithelium alone and LASIK. CONCLUSION: The intact corneal epithelium may play an important part curbing subepithelial haze and differentiation of myofibroblasts in corneal wound healing.     

Corneal haze after photorefractive keratectomy. Role of individual collagen type IV synthesis on postoperative corneal opacity

PURPOSE: Histological studies on human corneas have shown that collagen type IV plays a major role in the development of haze after photoreactive keratectomy (PRK). Currently, there is no clinically available pharmaceutical agent which can inhibit the synthesis of collagen IV. The aim of this study was to determine if there are individual differences in the expression of collagen IV and if there is a correlation between the amount of collagen IV and haze. This would give new options to prevent haze after PRK. PATIENTS AND METHODS: PRK was carried out on 26 eyes (26 patients) with a myopia ranging between -1.50 to -6.00 D. Prior to the surgery a small sample of epithelium was taken from the cornea and the individual concentration of collagen IV alpha 3 mRNA was quantitatively determined by a newly developed PCR test. RESULTS: In all samples collagen IV alpha 3 mRNA was measured with levels between 0.11 and 6.42 (mean: 1.68; SD: 1.64). There was a correlation between haze and the amount of collagen IV alpha 3 mRNA. (r = 0.92). CONCLUSIONS: With this quantitative PCR-based test we were able to measure the individual collagen IV mRNA concentration in corneal epithelial cells. Further development of this test could establish a screening test which identifies patients with a pronounced synthesis of collagen IV as high risk individuals in terms of haze.     

兔LASEK与PRK术后角膜Ⅰ、Ⅲ、Ⅴ、Ⅵ型胶原的Western Blot研究

目的:用WesternBlot法比较准分子激光上皮下角膜磨削术(LASEK)与准分子激光角膜切削术(PRK)术后角膜Ⅰ、Ⅲ、Ⅴ、Ⅵ型胶原的动态变化情况。方法:52只新西兰白兔分为8组,对每只兔右眼行LASEK,左眼行PRK。术后1d、7d、1个月、3个月、4个月、5个月、6个月观察Haze情况,处死动物取角膜行Ⅰ、Ⅲ、Ⅴ、Ⅵ型胶原的动态变化过程的免疫组织化学检查与WesternBlot检测。结果:经免疫组化和WesternBlot研究发现:LASEK组术后角膜基质中Ⅰ、Ⅲ型胶原开始增生的时间早于PRK组,表达的强度与PRK组有显著差异;两组的Ⅴ、Ⅵ型胶原动态变化曲线相似,达到表达高峰的时间一致,PRK组Ⅴ、Ⅵ型胶原的表达均明显高于LASEK组,术后6个月时LASEK组表达显著弱于PRK组。结论:PRK手术后角膜基质中Ⅰ、Ⅲ、Ⅴ、Ⅵ型胶原的表达强度、达到高峰及恢复正常的时间与LASEK相比存在显著差异,表明PRK术后基质内有胶原的过量沉积,可能是临床PRK术后Haze严重及屈光回退的组织学基础。WesternBlot法是一种可比较准确地半定量检测胶原含量动态变化的研究方法。     

Mitomycin C alters corneal stromal wound healing and corneal haze in rabbits after argon-fluoride excimer laser photorefractive keratectomy.

PURPOSE: To investigate the effects of mitomycin C (MMC) on rabbit cornea wound healing after photorefractive keratectomy (PRK). MATERIALS AND METHODS: Rabbit corneas were stained with dichlorotriazinyl aminofluorescein immediately after PRK. MMC was applied to the right eye and phosphate-buffered salt solution (PBS) to the left. Corneal epithelial wound healing rate and corneal haze were examined. Ultrasound pachymetry was performed. Stromal collagen regeneration was evaluated by fluorescent microscopy. We used terminal deoxyribonucleotidyl transferase-mediated D-uridine 5'-triphosphated-digoxigenin nick-end labeling (TUNEL) assay and transmission electron microscopy (TEM) to evaluate keratocyte apoptosis. RESULTS: In eyes treated with MMC, there was no delay to the healing rate of corneal epithelial wound, and less haze 4 weeks after PRK. Ultrasound pachymetry showed thinner corneal thickness in MMC-treated eyes at week 4. Corneal stromal thickness regression was less in MMC-treated eyes observed by fluorescent microscope at week 4. Keratocyte apoptosis was noted in both MMC- and PBS-treated eyes by TUNEL assay and TEM observation. This study discovered the phenomenon that MMC prolongs keratocyte apoptosis. CONCLUSIONS: Applying MMC after PRK is an effective method to decrease haze formation and corneal stromal thickness regression in rabbit corneas. The effect may be related to MMC prolonging keratocyte apoptosis.     

准分子激光术后大鼠角膜上皮下雾状混浊中Ⅰ型前胶原的测定

目的探讨准分子激光术后大鼠角膜中Ⅰ型前胶原的变化,比较角膜非手术区、手术野透明区与上皮下雾状混浊（haze）区的Ⅰ型前胶原含量的差异。方法32只6月龄清洁级SD大鼠按照手术前后被处死的时间不同平均分为8组。28只大鼠的一侧眼被施行准分子激光角膜切削术（PRK）。术后每日裂隙灯显微镜下观察术眼角膜情况,角膜haze的分级参照Seiler标准。分别于手术前和术后1、3、7、15d及1、2、3个月处死动物,行苏木精-伊红染色,观察手术区角膜的形态变化,采用免疫组织化学法检测角膜Ⅰ型前胶原在术眼角膜组织中的表达,并以光密度（OD）值表示。对不同时间采集的角膜非手术区、手术野透明区与haze区中Ⅰ型前胶原含量进行定量分析。结果臼术后3d起,术眼角膜上皮开始移行覆盖切削区并逐渐增厚,基质纤维细胞增生活跃;术后1个月时术眼角膜上皮基底膜开始形成,基质胶原纤维排列紊乱;术后3个月角膜基质胶原重塑过程基本完成,角膜结构趋于正常。大鼠角膜术后haze分级与Ⅰ型前胶原含量呈正相关（r=0．406,P〈0．05）;非手术区各时间段角膜平均OD值均无明显变化（t=5．719,P〉0．05）;手术区角膜中的Ⅰ型前胶原含量明显高于非手术区（P〈0．05）;haze区平均OD值明显高于非haze区（t=5．578,P〈0．05）。免疫组织化学检测表明,角膜上皮中Ⅰ型前胶原的阳性表达在术后7d最多,并终止于术后1个月,而角膜细胞间质中Ⅰ型前胶原持续至整个修复过程。结论Ⅰ型前胶原含量的增加可能是haze形成的主要因素之一,为进一步研究准分子激光术后角膜前胶原的变化提供理论支持。     

兔准分子激光角膜切削术后角膜血小板源性生长因子mRNA表达的变化

研究角膜上皮下混浊形成的发生机制,检测准分子激光屈光性角膜切削术后角膜上皮和基质血小板源性生长因子表达的变化。方法新西兰白兔施行ＰＲＫ后１,２,３月用裂隙灯显微镜观察ｈａｘｅ形成情况,并用原位酸分子杂交方法,检测角膜上皮和基质ＰＤＧＦ ｍＲＮＡ的表达。结果正常角膜上皮细胞有ＰＤＧＦ ｍＲＮＡ表达,基质层无表达;ＰＲＫ后角膜上皮细胞ＰＤＧＦｍＲＮＡ表达增加,术后２月表达最强,且基质中亦有轻微表达。上     

准分子激光屈光性角膜切削术后角膜上皮素mRNA的表达

目的：观察准分子激光屈光性角膜切削术（photorefractive keratectomy,PRK)术后，新西兰大白兔角膜组织愈合过程中角膜上皮素（keratoepithelin,KE)mRNA表达的变化，探讨KE与角膜雾状混浊（haze）的关系。方法：24只新西兰大白兔中的20只左眼按－10D行PRK术（另外4只为正常对照组），分别于术后7、14、28天、3个月和6个月行光镜、电镜和原位杂交检查。结果：正常角膜上皮和基质中未检测出KE mRNA；术后7、14、28天角膜上皮KE，mRNA表达阳性，术后3月和6月阴性；术后7天和14天基质中KE mRNA表达阳性，术后28天、3月和6月表达阴性。结论：角膜上皮素参与了PRK术后伤口愈合中细胞外基质的形成，可能在角膜组织的重建中起着重要的作用。     

The Changes of TGF—α,TGF—β1 and Basic FGF Messenger RNA Expression i

OBJECTIVE: To study the mechanism of haze formation and investigate the expression changes of transforming growth factor-alpha (TGF-alpha), transforming growth factor-beta 1(TGF-beta 1) and basic fibroblast growth factor (bFGF) mRNA in corneal epithelium and stroma after photorefractive keratectomy (PRK). METHODS: Sixteen white rabbits were randomly divided into 4 groups, and PRK was performed on each eye of 12 rabbits. The haze formation was examined under a slit-lamp microscope at the 1st, 2nd and 3rd month after PRK, and the expressions of TGF-alpha, TGF-beta 1 and bFGF mRNA were detected with in situ hybridization. RESULTS: The corneal haze formed at the 1st month after PRK. The most prominent haze formation was observed at the 2nd month, and declined gradually at the 3rd month after ablation. TGF-alpha mRNA expression was presented on the normal corneal epithelium and not on the corneal stroma. TGF-beta 1 and bGFG mRNA were expressed by both corneal epithelium and stroma. The capacities for cornea tissue expression of three growth factors mRNA increased after PRK, and the peaks appeared on the 1st, 2nd month. The extent for expressions of three growth factors related proportionally to the haze formation. CONCLUSION: Three growth factors took part in promoting corneal wound healing after PRK, and might contribute to corneal haze formation and development.     

氧化剂对准分子激光兔角膜切削术后细胞凋亡的影响

目的探讨氧自由基对准分子激光屈光性角膜切削术（PRK）后凋亡机制介导的角膜创伤愈合反应的作用,以及局部应用抗氧化剂维生素C（Vit C）、维生素E（Vit E）对术后角膜的影响。方法将28只兔分成3组,其中4只为正常对照;其余24只实验兔分成2组,每组12只,行双眼-5．0 DPRK。一组术后左眼每日结膜下注射VitC 0．1g,右眼为对照;另一组术后左眼每日结膜下注射VitE 25mg,右眼为对照。于术后1、3、7、14d测定角膜组织超氧化物歧酶（SOD）、丙二醛（MDA）及谷胱甘肽过氧化物酶（GPx）的变化,同时术后定期制作病理切片,检测角膜基质细胞数量,采用脱氧核苷酸末端转移酶介导的缺口末端标记法（TUNEL）检测角膜细胞凋亡,光镜观察凋亡细胞形态,定量统计比较凋亡水平差别。结果（1）PRK术后1、3d角膜SOD、GPx活性小于对照组（P〈0．05）,MDA的水平高于对照组（P〈0．05）。局部应用抗氧化剂组其角膜SOD、GPx活性高于单纯激光组（P〈0．05）,MDA水平低于单纯激光组（P〈0．05）。（2）角膜基质细胞凋亡在1～14d均与正常对照组有差别（P〈0．01）,在应用抗氧化剂组角膜基质细胞凋亡较单纯激光组减少（P〈0．05）。（3）术后角膜基质细胞数增加,应用抗氧化剂组角膜基质细胞增生较单纯激光组减少（P〈0．05）。结论准分子激光屈光性角膜切削术后早期,角膜存在着脂质过氧化形式介导的自由基性的组织损伤破坏,促进角膜细胞的凋亡;局部应用抗氧化剂VitC、VitE能早期减轻PRK术后炎性反应,降低角膜过氧化损伤,阻止术后细胞凋亡,减轻角膜基质反应性过度增生,降低术后屈光回退和haze形成。