猪眼LASIK术后角膜的应力-应变关系和本构方程

目的:研究LASIK术后角膜材料的应力—应变关系,建立其本构方程,分析其生物力学特性。方法:猪眼LASIK手术后,角膜试样单轴拉伸实验。结果:猪眼LASIK手术中,随基质切削深度的增加,角膜的弹性模量减少,各切削深度组均小于正常未做手术组,有显著的统计学差异(P<0.01);30%基质切削深度与单纯做瓣组比较,角膜的弹性模量接近,差异无统计学意义(P>0.05);角膜材料发生屈服的临界点对应的应变在30%左右。角膜材料没有明显的屈服阶段。基质消融50%以上时,角膜的垂直轴向屈服强度明显小于水平轴向的屈服强度(P<0.01)。结论:LASIK手术中,当30%整体角膜厚度的基质激光消融时,角膜仍维持其粘弹性材料特征。     

不同角膜切削深度的准分子激光原位角膜磨镶术对兔角膜的影响

目的 比较不同切削量的准分子激光原位角膜磨镶术（LASIK）术后眼角膜生物力学特性及角膜变形的情况.方法 选取成年新西兰白兔16只（32眼）随机分成A、B、C、D四个组.A、B、C组均行LASIK手术,使残留的基质床厚度分别为全层角膜厚度的30%、50%、70%;D组不行切削手术,作为对照组.术后6个月对兔眼行角膜地形图检查;对条状角膜在Instron试验机上进行单向拉伸和拉伸蠕变实验,用最小二乘法拟合得出不同切削量的角膜在蠕变实验中的弹性系数.结果 术后6个月,角膜地形图检测结果显示,A组角膜切削区的中央部较周边膨隆;B、C组均未发现角膜膨隆和圆锥角膜.与对照组比较,A、B组LASIK术后角膜的弹性模量有统计学意义（P〈0.05）,C组无统计学意义.结论 LASIK术后6个月,角膜刚度系数随角膜切削量的增加而减小,角膜抗拉能力也随之减小,但使剩余的基质床厚度保留至全层角膜厚度的50%时是否会造成继发性圆锥角膜尚需进一步的研究.     

PRK和LASIK对非接触眼压计测量值的影响

目的 :研究PRK和LASIK手术前后非接触眼压计 (NCT)测量值的改变及其与切削深度的相关性。方法 :对不同屈光度患者 673只眼 (PRK 3 2 5眼、LASIK 3 48眼 )术前、术后 3、 6、 12个月的眼压、角膜厚度及切削深度 ,应用统计学方法检验 ,并对眼压改变值与术中角膜切削深度作相关性分析。结果 :术后角膜厚度随屈光度增加而变薄 ,LASIK组大于PRK组 :NCT测量值均明显低于术前 ,差异有显著性 (P <0 0 5 ) ,但LASIK组与PRK组差异无显著性。术后一年眼压下降值与术中角膜切削深度存在统计学上的相关性 :PRK组r =0 2 85 6,LASIK组r =0 2 5 3 8。结论 :PRK和LASIK术后NCT测量结果下降 ,角膜变薄是其主要原因。     

飞秒激光LASIK术后早期不同部位角膜敏感性变化研究

目的 评估飞秒激光LASIK术后早期角膜中央和周边区敏感性的恢复情况.方法 观察飞秒激光LASIK手术的患者40例(71只眼),分别在术前、术后1周、1月、3月使用Cohet-Bonnet角膜知觉计检查角膜中央、上方、下方、鼻侧和颞侧五个部位的敏感性,统计方法采用Kruskal Wallis H秩和检验和Mann-Whitney检验,以P＜0.05表示有统计学意义.结果 飞秒激光LASIK手术后早期,在五个测量部位,术后1周、1月、3月角膜敏感性均低于术前,差异具有统计学意义(P＜0.05).术后1周、1月、3月各个时间段,角膜上方敏感性均高于其他部位,差异具有统计学意义(P＜0.05).术后3个月,中央区角膜敏感性小于其他部位,差异具有统计学意义(P＜0.05).中央角膜敏感性与角膜中央切削深度、中央角膜厚度、术前等效球镜度无相关性(r=0.005;-0.105;0.03,P=0.97;0.38; 0.80).结论 飞秒激光LASIK术后早期角膜敏感性明显下降,角膜瓣蒂所在位置的敏感性较其他位置下降程度低,中央区角膜敏感性的恢复慢于其他位置,角膜中央敏感性与中央切削深度、角膜中央厚度、术前等效球镜度无相关.     

飞秒激光在猪眼角膜板层切削中的实验研究

目的:探讨飞秒激光在离体猪眼角膜行板层切削的切削深度、平滑度及可行性。方法:新鲜离体猪眼及甘油保存复水猪眼各10只,利用飞秒激光进行板层切削。激光切削前后对角膜进行测厚,计算角膜瓣厚度。同时选择徒手制作同样直径角膜瓣,扫描电镜观察两种方法制瓣的角膜基质面的形态区别。结果:新鲜离体猪眼角膜瓣厚度为394.10±12.04μm,甘油保存复水后猪眼角膜瓣厚度为366.30±15.28μm。飞秒激光切削的角膜表面较徒手剥离的角膜表面光滑。结论:飞秒激光在离体猪眼表面切削深度与设定切削深度存在差异,其切削表面光滑,在角膜移植中具有广泛应用前景。     

LASIK和Epi-LASIK术中角膜切削误差及术后角膜地形图变化比较

目的 探讨准分子激光原位角膜磨镶术(LASIK)和准分子激光上皮下角膜磨镶术(Epi-LASIK)术中角膜切削误差及术后角膜地形图变化.方法 选取2012年2月至2014年8月我院行近视激光矫正手术患者211例(403只眼)作为研究对象,随机分为LASIK组和Epi-LASIK组,其中LASIK组110例(209只眼),Epi-LASIK组为101例(194只眼),分别采取相应手术,观察术后两组患者角膜切削误差及术前与术后1、3个月两组高度近视患者角膜地形图形态Simk差值、Simk等效值、CIM值及SF绝对值4个参数变化.结果 两组中轻中度近视患者角膜切削误差无显著差异(P＞0.05),Epi-LASIK组中高度近视患者的角膜切削误差显著小于LASIK组(P＜0.05);两组高度近视患者术前角膜图形均以对称领结型及非对称领结型为主,两组各形态间无显著差异(P＞0.05);两组高度近视患者术后角膜地形图形均以平滑型为主,LASIK组的平滑型显著低于Epi-LASIK组(P＜0.05),其余形态两组比较无显著差异(P＞0.05);在Simk差值、Simk等效值上,两组术后结果均显著低于术前(P＜0.05),两组间术后结果对比无显著差异(P＞0.05);在CIM值上,两组术后结果均显著高于术前(P＜0.05),LASIK组术后结果均显著高于Epi-LASIK组(P＜0.05);在SF绝对值上,两组术后结果均显著低于术前(P＜0.05),两组间术后结果对比无显著差异(P＞0.05).结论 Epi-LASIK可有效降低术中角膜切削误差及改善术后角膜地形图参数,有利于增强手术的效果,促进术后患者的恢复及改善患者预后,可在临床检查中广泛推广.     

近视眼二次LASIK手术临床疗效分析

目的:探讨近视眼二次LASIK手术病例临床特点、有效性和安全性。方法:回顾性系列病例研究。44例近视患者(72眼)接受二次LASIK,二次手术间隔时间为13.32±12.06(3～58)mo,二次LASIK术前平均残余屈光不正度为-2.56±1.56(-7.25～+1.13)D;分析年龄、屈光度、角膜中央厚度、角膜瓣厚度、残余角膜基质厚度的特点及其对残余屈光不正度的影响。结果:二次术后UCVA为0.89±0.19(0.5～1.2)μm,等效球镜度(SE)为0.05±0.57D。二次术前CCT为502.69±31.45μm,与理论残余的456.08±26.04μm差异有统计学显著性意义(t=-0.785,P=0.000);多元回归分析表明,在诸多因素中,术前预矫屈光度和切削深度对二次术前屈光度有显著性影响(F=73.442,P=0.000),回归方程:残余屈光不正度=-0.317+0.588×术前等效球镜+0.031×切削深度。结论:本组二次LASIK手术病例表明,预矫屈光度和切削深度是导致屈光回退的主要因素;术后角膜组织增生是LASIK远期屈光回退的机制之一;在严格控制角膜厚度和预矫屈光度的前提下,二次LASIK是安全、有效的。     

LASIK术中用飞秒激光制瓣的临床观察

目的 观察LASIK术中使用飞秒激光制作角膜瓣的临床效果及分析飞秒激光仪制作不理想瓣的处理方法.方法 将2402例(4697眼)应用飞秒激光制作角膜瓣后行LASIK的近视患者.根据术前设计角膜瓣厚度分成90 μm的255例(479只眼),110 μm 2091例(4138只眼),140 μm 56例(80只眼),术后1周使用傅立叶光学相干断层扫描测量角膜瓣的实际厚度进行分析.结果 术后1周实际角膜瓣厚度:90 μm角膜瓣平均厚度[90.54±6.06(82～ 101 )]μm,110 μm角膜瓣平均厚度[109.79±7.62(103～116)]μm,140μm角膜瓣平均厚度[138.85±5.68(129～147)]μm,术后实际角膜瓣厚度与术前预先设计角膜瓣厚度差异无统计学意义(P＞0.01).在制瓣过程中,出现5种不理想的角膜瓣问题:角膜切削基质面中心颗粒大、角膜切削面基质面有条纹、角膜切削基质面条形粘连、角膜切削基质面中心粘连、飞秒激光切削角膜后角结膜结合处出现气泡,并总结其处理方法.结论 飞秒激光制作角膜瓣行LASIK,切削精确、安全性高,在一定程度上可抑制手术造成的像差、提高对比敏感度.     

高度近视LASIK术后眼压值的变化

目的 探讨LASIK治疗高度近视术后眼压变化与角膜切削量的关系.方法 427例高度近视患者按屈光度分成A组(-6.0D至-10.00D)和B组(-10.0至-21.0D),施行LASIK术前后用非接触眼压计(NCT)测量眼压,并分析其与角膜切削量的关系.结果 两组眼压术后明显下降.A组为12.21±3.22 mmHg;B组为10.48±2.76mmHg(P＜0.001).角膜切削量占术前角膜中央厚度A组为12.4～18.9 %;B组为19.0～34.7 %(P＜0.01).结论 LASIK治疗高度近视术后NCT眼压值下降与角膜中央厚度变薄和抗压强度减弱有关.     

近视眼LASIK术后角膜不规则散光的临床分析

目的 :定量分析LASIK术后角膜不规则散光改变与激光切除量的关系。方法 :对近视眼行LASIK手术 ,术前和术后一个月测量角膜地形图 ,计算角膜不规则散光 ,采用傅立叶函数分析方法对数据进行分析。结果 :LASIK术后 ,角膜不规则散光的程度明显增高 (P <0 .0 0 0 1) ,不规则散光程度与切削的深度显著相关 (r =0 .44 0 ,P <0 .0 0 0 1)。结论 :LASIK手术明显增高角膜的不规则散光 ,其不规则散光的程度与激光切削量密切相关。     

Experimental assessment of corneal anisotropy

PURPOSE: To determine the variation of corneal biomechanical properties with anatomical orientation. METHODS: Strip specimens extracted from fresh porcine corneas were tested under uniaxial tension with strain rates representing static and dynamic loading conditions. The specimens were extracted from the vertical, horizontal, and 45 degrees diagonal directions. The load elongation results were used to derive the stress-strain behavior of each specimen. The average behavior for specimens taken in each anatomical direction was determined along with the effect of strain rate. Specimens from a small number of human corneas were included in the study to verify the findings. RESULTS: Specimens extracted from the vertical direction of porcine and human corneas demonstrated the highest strength (fracture stress) followed by horizontal then diagonal specimens. Vertical specimens were 10% to 20% stronger than horizontal specimens in porcine and human corneas. At low strain rates (1%/min), vertical specimens displayed similar stiffness (resistance to deformation) to horizontal specimens but greater stiffness than diagonal specimens. On increasing the strain rate to 500%/min, the stiffness behavior matched that of strength with vertical specimens being 10% to 20% stiffer than horizontal specimens in porcine and human corneas. CONCLUSIONS: The corneal anisotropic behavior is compatible with the preferential orientation of stromal fibrils in the vertical and horizontal directions. Quantifying the effect of this nonuniform fibril organization on corneal anisotropic behavior will be useful in developing numerical models of the cornea for applications where its integrity is compromised such as in simulating refractive surgery procedures.     

Change in corneal sensitivity following laser in situ keratomileusis

PURPOSE: To evaluate the change in corneal sensitivity following laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, Maryknoll Hospital, Pusan, Korea. METHODS: The corneal sensitivity in 40 eyes (32 patients) was measured before and 1 and 2 weeks and 1, 3, and 6 months after LASIK. Sensitivity measurements were made with an esthesiometer at central, temporal, inferior, nasal, and superior points on the corneal flap. The eyes were grouped by ablation depth: Group 1, corneal ablation depth less than 100 microns; Group 2, corneal ablation depth more than 100 microns. RESULTS: Corneal sensitivity did not recover to the preoperative level by 6 months after LASIK. Except at the hinge of the corneal flap, the pattern of sensitivity recovery was similar among the various points. Recovery was more rapid at the hinge than at other areas (P < .05). There was a trend toward a greater reduction in corneal sensitivity in Group 2, the group with deeper ablations, than in Group 1. CONCLUSION: The results suggest that lamellar cutting of the cornea during LASIK impairs corneal sensitivity and that the depth of the corneal ablation affects the extent of corneal sensitivity loss and recovery.     

兔眼准分子激光近视角膜切削术后角膜膨出的研究

目的：探讨兔眼在准分子激光近视角膜切削术（Excimer laser in-situ keratomileusis,LASIK)手术后在不同的眼压下角膜膨出的程度。方法：26兔52眼随机分为对照组，LASIK手术组，单盲法，术前，术后测量角膜厚度和角膜地形图后，再将两组随机交叉分为正常眼压组，低度高眼压组，高度高眼压组，并观察1个月，用角膜地形图对实验前后的角膜形态进行分析。并应用统计学方法将手术切削量和眼压两个因素对角膜扩张的影响做双因素方差分析。结果：LASIK手术的角膜切削量，术后高眼压以及两者的交互效应对角膜抵抗力都有显著影响。较大的切削量和术后持续高眼压后的兔眼角膜地形图经分析符合圆锥角膜模式，并出现前，后弹力膜断裂的形态学改变。结论：角膜较大的切削量和术后持续的高眼压是导致兔眼LASIK术后发生圆锥角膜的重要原因。     

Posterior corneal topographic changes after retreatment LASIK

PURPOSE: To evaluate posterior corneal topographic changes after retreatment after myopic laser in situ keratomileusis (repeat LASIK). DESIGN: Retrospective nonrandomized comparative self-controlled trial. PARTICIPANTS: Thirty-three eyes of 23 patients who underwent repeat LASIK for residual myopia. INTERVENTION: Retreatments were performed. Slit-scanning corneal topography was performed before and at 1, 3, and 6 months after repeat LASIK. MAIN OUTCOME MEASURES: Posterior corneal topographic changes before and after repeat LASIK were correlated with central corneal pachymetry (preoperatively, before repeat LASIK, after repeat LASIK), residual bed thickness (RBT) and ablation depth (after primary laser in situ keratomileusis (LASIK) and repeat LASIK). On the basis of the amount of posterior corneal elevation after repeat LASIK, the eyes were divided into two groups: group 1 (>66 micro m) and group 2 (< or =66 micro m). Student's t test/Mann-Whitney rank-sum test was used to determine the significant difference of mean level of each variable between the two groups. RESULTS: After primary LASIK, an increase in posterior corneal elevation had significant positive correlation with attempted correction (P = 0.02), ablation depth (P = 0.008), and significant negative correlation with preoperative central pachymetry (P = 0.0003), RBT (P = 0.0003), and postoperative central pachymetry (P = 0.00008). After repeat LASIK, the mean increase in posterior corneal elevation had significant negative correlation with preoperative central pachymetry (P = 0.03). However, its correlation with the ablation depth (P = 0.43) during repeat LASIK and RBT after repeat LASIK (P = 0.11) was statistically insignificant. On multiple linear regression analysis, the attempted correction (P < 0.01) and RBT after primary LASIK (P < 0.001) were two independent significant determinants of an increase in posterior corneal elevation after primary LASIK. However, for increase in posterior corneal elevation after repeat LASIK, preoperative central pachymetry (P < 0.01) and posterior corneal elevation increase after primary LASIK (P < 0.05) were the two significant determinants. Compared with group 2, group 1 had significantly high values of posterior corneal elevation both after primary LASIK (P = 0.0037) and after repeat LASIK (P = 0.0000). This group also had significantly low values of central pachymetry preoperatively (P = 0.0003) and after primary LASIK (P = 0.0001) and repeat LASIK (P = 0.0001) surgeries. The mean RBT after primary LASIK (P = 0.0006) and after repeat LASIK (P = 0.001) was also lower in group 1. CONCLUSIONS: Posterior corneal elevation increases after repeat LASIK. Eyes with an increase in posterior corneal elevation after primary LASIK and with thinner cornea are more predisposed.     

LASIK术中实际角膜切削深度的临床研究

目的:观察NIDEK EC5000准分子激光治疗系统准分子激光原位角膜磨镶术(Laser in situ kemtomileusis,LASIK)角膜切削深度的可预测性.方法:采用NIDEK EC5000准分子激光系统对79例近视和(或)近视散光患者进行标准LASIK手术,术中使用超声角膜测厚仪分别测量制瓣后和激光切削后的剩余角膜床厚度,计算实际角膜切削深度,比较实际角膜切削深度同理论预测角膜切削深度的差异.结果:LASIK术中实际切削深度(92.32±29.86)μm,预测切削深度(74.16±25.95)μm,两者差值(18.16±14.71)±m有统计学意义(P＜0.001).实际切削深度与预测切削深度具有较好的相关性,相关系数为0.87(P＜0.001),其直线回归方程为Y=18.06±1.001X.按术前角膜K值、术前等效球镜绝对值及术前中央角膜厚度值分组的实际切削深度与预测切削深度的差值均有统计学意义.实际切削深度与术前等效球镜有关,与术前中央角膜厚度和K值无关.实际切削深度与预测切削深度差值同K值、等效球镜、术前中央角膜厚度均无关.结论:NIDEK EC5000 准分子激光系统LASIK 术中实际角膜切削深度比预测角膜切削深度高(18.16±14.71)μm,在手术设计时要考虑实际切削与机器标示值存在偏差,应尽可能多的预留剩余角膜基质床厚度,以提高手术安全性.     

Corneal irregular astigmatism after laser in situ keratomileusis for myopia

AIMS: To quantitatively evaluate the changes in corneal irregular astigmatism after laser in situ keratomileusis (LASIK) in relation to the amount of laser ablation. METHODS: In 189 eyes of 116 patients undergoing LASIK for myopia, corneal topography was obtained before and 1 month after surgery. Using Fourier harmonic analysis of the topography data, corneal irregular astigmatism (asymmetry and higher order irregularity) was calculated. RESULTS: By surgery, asymmetry component significantly increased (p < 0.0001, Wilcoxon signed rank test), while higher order irregularity did not (p = 0.767). The increases in the asymmetry component significantly correlated with ablation depth (Spearman rank correlation coefficient r(s) = 0.440, p < 0.0001). No significant correlation was found between changes in higher order irregularity and ablation depth (r(s) = 0.137, p = 0.074). CONCLUSION: LASIK significantly increases the asymmetry component of the cornea which is dependent on the amount of laser ablation.     

传统与个体化LASIK术中实际角膜切削深度的对比研究

目的：对比研究传统与个体化准分子激光原位角膜磨镶术（laser in situ keratomileusis,LASIK）中实际角膜切削深度的差异。方法：前瞻性对照研究,随机选取采用Technolas 217z100型准分子激光机进行LASIK手术的中低度近视及近视散光患者87例161眼,分为传统切削组和个体化切削组。术中采用光学相干厚度测量仪（online optical coherence pachymetry,OCP）实时监测所有患者的角膜厚度,并记录掀瓣后激光切削前及切削后的角膜基质厚度,计算出实际角膜切削深度。比较各组实际角膜切削深度与理论切削深度的差异及两组实际角膜切削深度与理论切削深度差值的组间差异。结果：传统切削组实际角膜切削深度为94.37±22.76μm,理论切削深度为85.69±21.19μm,差异有统计学意义（P〈0.05）。个体化切削组实际角膜切削深度为90.08±15.98μm,理论切削深度为76.30±13.65μm,差异有统计学意义（P〈0.05）。传统切削组实际角膜切削深度较理论切削深度增加8.68±6.30μm,个体化切削组实际角膜切削深度较理论切削深度增加13.78±7.63μm,差异有统计学意义（P〈0.05）。个体化切削组实际角膜切削深度与理论切削深度差值较传统切削组切削深度差值增加5.10±1.10μm。结论：传统LASIK及个体化LASIK术中实际角膜切削深度均比理论切削深度增加。个体化LASIK中实际角膜切削深度偏差较传统LASIK切削深度偏差更大。     

Effect of lamellar flap location on corneal topography after laser in situ keratomileusis

PURPOSE: To investigate the effect of hinge position on corneal topography after laser in situ keratomileusis (LASIK) for myopia. SETTING: Academic center and refractive surgery practice. METHODS: Topography data obtained from 89 eyes of 46 patients after LASIK were analyzed. Using a system of Cartesian coordinates, data along the horizontal and vertical axes were analyzed, measuring sagittal height and power change at 1 mm intervals from the ablation zone center. Data points that were equidistant and on opposite sides of the ablation center were compared to find asymmetry along either axis relative to nasally hinged flaps. RESULTS: Along the horizontal axis, areas of the cornea closer to the hinge had a higher topography than areas farther from the hinge. Specifically, the points nearest and farthest from the hinge were significantly different in sagittal height (P <.034); the areas farthest from the hinge were reduced more after surgery (relatively lower topography). When results were stratified into low- and high-diopter corrections, this difference was significant in only the high-diopter group (P <.0006). Trends in power change were also observed. Areas of the cornea closer to the hinge were relatively flatter than areas farther from the hinge. Statistical significance was detected in only the low-diopter group at data points 2 mm from the ablation zone center in opposite directions (P <.008). No asymmetry was seen along the vertical axis in power change or sagittal height. CONCLUSIONS: The lamellar flap in LASIK may influence postoperative corneal topography. Hypothetically, the corneal flap may retract toward the hinge, producing axial asymmetry in the postoperative topography relative to the hinge. Understanding the influence of corneal flap characteristics on post-LASIK topography may improve optical results and may be particularly important in the development and effectiveness of topography-guided ablation techniques.