高度近视患者LASIK术后角膜后表面曲率变化的析因分析研究

目的观察准分子激光原位角膜磨镶术（LASIK）术后角膜后曲率的变化,并研究角膜后表面曲率变化与术前眼压及承载因子（术前角膜中央厚度/残留角膜基质床厚度）的关系。方法采用ORBSCANⅡ裂隙扫描角膜地形图系统对高度近视患者40例（80只眼）LASIK术前和术后1、2、3个月及6个月的角膜后表面曲率进行测定,分析LASIK术后角膜后表面曲率的变化,并按术前眼压及承载因子分成4组,对LASIK术后角膜后表面曲率变化与术前眼压、承载因子进行析因分析研究。结果高度近视眼LASIK术后角膜后表面均有不同程度的向前膨隆,LASIK术后1个月较术前角膜后表面曲率半径变化为（0.135±0.098）μm,LASIK术后2个月较术后1个月角膜后表面曲率半径变化为（0.022±0.034）μm。结论高度近视眼LASIK术后早期角膜后表面均有不同程度的向前膨隆,LASIK术后2个月时角膜后表面曲率基本稳定。且术前眼压越高、承载因子越大,术后角膜膨隆越明显。     

准分子激光原位角膜磨镶术术后早期角膜空间变化

目的研究和分析近视性准分子激光原位角膜磨镶术(laser in stitu keratomileusis,LASIK)术后角膜空间变化规律。方法采用眼前节扫描系统(ORBSCANⅡ)观察48例(89眼)LASIK术前及术后1~3 d、第1周、第1个月、第3个月、第6个月的角膜前后表面高度和角膜最薄厚度的变化。结果术后角膜前表面高度迅速变平,到第1周时达最大量,此后至术后第6个月缓慢回升;术前等效球面镜度数和角膜基质床厚度与术后第3个月的角膜前表面高度变化呈直线正相关,切削比百分数(切削厚度占最薄角膜厚度比)与之呈直线负相关。LASIK术后角膜后表面即前凸,并达最大量,术后第1周时较快回落,此后至术后第6个月缓慢回落;术前等效球面镜度数、术前最薄角膜厚度、角膜基质床厚度与术后第3个月角膜后表面高度变化呈直线负相关,切削比百分数与之呈直线正相关。术后1~3 d角膜最薄,厚度最小,随着时间延长至术后第6个月均逐渐增厚,但速度逐渐减慢;术后1~3 d的实际角膜最薄厚度平均为(424±65.0)μm,比预计角膜最薄厚度平均值(463.9±42.1)μm低,差异有显著性(t=3.218,0.001相似文献   

LASIK后角膜后表面曲率变化

目的观察LASIK术后角膜后曲率的改变,并研究其与残留角膜床厚度的关系.方法采用ORBSCAN裂隙扫描角膜地形图系统对32只眼LASIK手术前和手术后三个月角膜后表面曲率进行测定.结果LASIK术后角膜后表面均有不同程度的向前突出,残留角膜床厚度大于250μm者,平均前突7±6μm,而在高度近视患者剩余角膜床厚度小于250μm,术后角膜后表面中央前突达22±9μm.结论LASIK术后角膜后表面前凸增加,残留角膜床小于250μm者术后发生角膜扩张的危险性可能增加.     

准分子激光原位角膜磨镶术后角膜后表面Diff值的变化

目的 探讨近视患者准分子激光原位角膜磨镶术（LASIK）术后角膜后表面Diff值变化规律及其对术后视力的影响.方法 对62例（123眼）近视患者于LASIK术前、术后1 d、1周、1个月行角膜地形图检查.分别按照残余基质床厚度、残余基质床厚度占术前角膜厚度的比例及术前屈光度的不同分组,分析各组间及同一组不同时期角膜地形图后表面Diff值的改变及其与术后视力的关系.结果 术后后表面Diff值较术前增大,且随原屈光度增大而增加,随基质床厚度增大而减小.当残余基质床厚度〉300μm或残余基质床厚度占术前角膜厚度的比例≥55%时,后表面Diff值明显减小.术后后表面Diff值与视力呈一定程度负相关.结论 LASIK术后角膜后表面前凸是影响术后视力的原因之一.后表面前凸的主要影响因素包括术前屈光度的高低、残余基质床厚度等,残余基质床厚度在300 μm以上或残余基质床厚度占术前角膜厚度的比例≥55%也许更安全.     

准分子激光原位角膜磨镶术后角膜后表面高度研究

目的 观察准分子激光原位角膜磨镶术(LASIK)术后角膜后表面高度的改变,探讨角膜后表面膨隆与剩余角膜基质床厚度(RBT),以及与激光切削所占角膜厚度比例(AP/TCT)的关系.方法 回顾分析LASIK 157例(157眼),根据RBT分组:组1为79眼,RBT≥350 μm;组2为52眼,300 μm≤RBT＜ 350 μm;组3为26眼,250 μm≤RBT＜ 300 μm.根据AP/TCT分组:组A为44眼,AP/TCT≤10%;组B为84眼,10%＜AP/TCT≤20%;组C为29眼,AP/TCT＞ 20%.术前、术后1周、术后1个月、术后3个月、术后6个月应用OrbscanⅡ行角膜地形图检查,分析比较各组各个不同时间点的角膜后表面膨隆程度.结果 角膜后表面高度各组术后1周、术后1个月、术后3个月、术后6个月与术前比较,差异均有统计学意义(P均＜0.05);术后同一时间点,组1、组2、组3组间及组A、组B、组C组间角膜后表面高度差异值( PED)两两比较差异有统计学意义(P均＜0.05).术后6个月PED值与RBT呈线性负相关(r= -0.77,P=0.00);与AP/TCT呈线性正相关( r=0.90,P=0.00),且与AP/TCT相关性更好.结论 LASIK术后角膜后表面均有不同程度的膨隆,并与RBT和AP/TCT相关;RBT不应为LASIK术后评价角膜后表面膨隆风险的唯一指标,AP/TCT是重要补充指标.(中国眼耳鼻喉科杂志,2011,11:215-218)     

准分子激光原位角膜磨镶术后角膜后表面的改变

目的 :研究准分子激光原位角膜磨镶术 (LASIK)后角膜后表面的改变 ,分析角膜后表面变化的相关影响因素。方法 :对 5 3例 96只眼施行LASIK手术 ,术前与术后 1个月使用裂隙扫描角膜地形图系统检测角膜后表面的高度及屈光度差异 ,分析角膜后表面前凸量与术前等效球镜度数、角膜中央厚度、术前眼压、激光切削量、切削百分比等因素的关系。结果 :LASIK术后 ,角膜后表面平均前凸量为 (33.4±2 4 .4 ) μm ,平均屈光度变化量为 (- 0 .6 7± 0 .4 2 )D ,术前术后的变化均具有显著性。与前凸量相关的可解释变量为术前角膜厚度 (偏回归系数B =- 0 .4 4 7,P <0 .0 0 0 1)、切削比 (B=15 4 .77,P =0 .0 0 1)和术前眼压 (B =2 .0 31,P =0 .0 2 4 )。结论 :LASIK术后角膜后表面普遍存在轻微的前凸 ,角膜较薄、眼压较高及切削比较大的受试眼术后角膜后表面前凸程度更大。     

LASIK术后5年内角膜后表面曲率和中央角膜厚度变化

目的 采用OrbscanⅡ角膜地形图仪对准分子激光原位角膜磨镶术（LASIK）后角膜后表面曲率和中央角膜厚度进行5年随访测量,探索其变化规律。方法 回顾性系列病例研究。LASIK手术患者48例（48眼）,平均屈光度（-6.25±2.87）D。术前及术后1个月、3个月、6个月、9个月、1年、2年、3年、5年,采用OrbscanⅡ测量其角膜后表面曲率（中央6 mm区域）和角膜厚度。采用重复测量的方差分析和LSD法比较角膜后表面曲率和中央角膜厚度的变化,并对两者关系作Pearson相关分析。结果 ①角膜后表面曲率变化：术后1个月,角膜后表面曲率较术前升高（t=8.211,P<0.01）;术后1~9个月,数值无明显变化,前后差异无统计学意义;术后9个月至2年,角膜后表面曲率逐渐下降,前后比较差异有统计学意义（t=-4.640、-2.659,P均＜0.01）;2年后,角膜后表面曲率趋于稳定,前后差异均无统计学意义。②中央角膜厚度变化：术后1个月,中央角膜厚度较术前下降（t=10.08,P<0.01）;术后1~9个月,中央角膜厚度逐渐上升,前后差异有统计学意义（t=-5.402、-4.428、-2.334,P均＞0.05）;术后9个月,中央角膜厚度趋于稳定,前后差异无统计学意义。③LASIK术后角膜后表面曲率与中央角膜厚度呈负相关（r=-0.703,P<0.01）。结论 LASIK术后早期角膜后表面中央区前凸,中央角膜厚度增加,此后两者均趋于稳定。随访期内角膜后表面曲率与中央角膜厚度呈负相关。     

准分子激光原位角膜磨镶术后角膜后表面曲率的改变

LASIK术后角膜层间反应轻,角膜瓣与瓣下基质之间不形成瘢痕组织,角膜的愈合方式虽然保留了清晰的视觉光区,但是角膜的组织结构发生改变可能是导致角膜强度发生变化的主要原因。LASIK术后角膜后表面曲率均有不同程度的向前凸,这与角膜中央厚度、残余角膜基质床的厚度、矫正的屈光度数、术前眼压、角膜瓣厚度、切削深度、切削区的直径、年龄等有关。本文就LASIK术后角膜后表面曲率的变化及影响因素展开综述。     

Sirius角膜地形图仪测量LASIK和LASEK术后角膜后表面的研究

目的通过Sirius角膜地形图仪测量LASIK和LASEK术后角膜后表面,分析其变化特点．评价各因素对角膜后表面变化的影响。方法前瞻性临床研究。人选2012年5月至2013年7月在宁波第一医院行准分子激光屈光手术患者,其中LASIK手术37例（74眼）,LASEK手术26例（52眼）,术前应用Sirius角膜地形图仪测量每眼．并完善术前常规检查,记录相关数值。记录患者术中的切削深度、切削比例、残留基质厚度,术后1周、1个月、3个月复查。各时间点之间数据比较应用重复测量资料方差分析．各变量与角膜后表面高度变化量之间的影响程度应用多元线性回归。结果LASIK与LASEK术后1周、1个月和3个月角膜后表面高度与术前比较稍增高,差异有统计学意义（F=43.58、7.51,P〈0.01）;残留基质对LASIK术后1周、1个月和3个月后表面高度变化量有影响（f=-3.421、-3.376、-3.116,P〈0.01）,对LASEK术后1个月和3个月后表面高度变化量有影响（t=-3.077、-2.872,P〈0.01）。结论Sirius角膜地形图仪测定显示LASIK、LASEK术后均表现为角膜后表面微量前移。残留基质厚度对角膜后表面变化影响较大。     

用Pentacam系统研究LASIK术后角膜后表面高度及曲率变化

目的应用Pentacam眼前节分析系统研究准分子激光原位角膜磨镶术(LASIK)术后角膜后表面高度及曲率的变化,探讨准分子激光手术对角膜后表面高度及曲率变化的影响因素。方法对200例(398只眼)施行LASIK的完整患者资料进行回顾性分析,分别于术前及术后3个月应用Pentacam系统对患者的角膜后表面高度及曲率进行检查并分析。结果角膜后表面高度变化在轻度近视组、中度近视组及高度近视组各组间比较差异具有统计学意义(P<0.05);后表面曲率变化在轻度近视组与中度近视组、高度近视组间比较差异均具有统计学意义(P<0.05),而中度近视组、高度近视组间比较差异无统计学意义(P>0.05)。角膜后表面高度及曲率变化在角膜床厚度250～280μm组与281～320μm组间、250～280μm组与>320μm组间比较差异具有统计学意义,在281～320μm组与>320μm组间比较差异无统计学意义(P>0.05)。结论 LASIK术后角膜后表面向前突,后表面高度增加,曲率负值增加,术前等效球镜越小、角膜床厚度越厚,角膜后表面高度及曲率变化越小。     

Long-term stability of the posterior cornea after laser in situ keratomileusis

PURPOSE: To study long-term changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) using Scheimpflug topography (Pentacam, Oculus, Inc.) in eyes 1 year after LASIK. SETTING: Department of Ophthalmology, Albany Medical Center, and a private practice, Albany, New York, USA. METHODS: One hundred two myopic eyes of 52 consecutive patients presenting for their 1-year follow-up were prospectively evaluated using the Pentacam to determine elevation changes to the posterior corneal surface between preoperative and 1-year postoperative measurements. Changes in posterior elevation were performed by comparing the best-fit sphere preoperatively and postoperatively with a fixed reference sphere determined by the central 9.0 mm preoperative cornea. Statistical and graphical analyses were performed. RESULTS: One hundred two post-LASIK eyes (mean correction -4.33 diopters; mean ablation depth 68.70 microm; mean estimated residual bed thickness 327 microm) had a mean posterior displacement of -0.47 microm +/- 3.48 (SD) (range -10.0 to +7 microm). The mean follow-up period was 13.6 months (range 8.8 to 19.3 months). CONCLUSIONS: In this population, no patient had significant forward protrusion of the posterior corneal surface a mean of 14 months after LASIK. The posterior cornea in post-LASIK myopic eyes was very stable. Contrary to results in previous studies, progressive changes to the posterior corneal surface did not routinely occur after LASIK performed within established parameters.     

Delayed ectasia following LASIK with no risk factors: is a 300-microm stromal bed enough?

PURPOSE: To report a case of ectasia occurring > 4 years following LASIK with no risk factors and a residual stromal bed > 300 microm. METHODS: A 33-year-old woman presented 4 years after LASIK with mild blurring in the left eye. Uncorrected visual acuity (UCVA) had been 20/20 in both eyes previously. RESULTS: Uncorrected visual acuity was 20/20 and 20/40 in the right and left eyes, respectively. Best spectacle-corrected visual acuity (BSCVA) was 20/20 with -0.75 +2.25 x 70 degrees refraction in the left eye, which matched topography. Preoperative corneal thickness was 595 microm, and topography showed no risk factors preoperatively or immediately postoperatively. Calculated residual stromal bed was 342 microm and measured 400 microm with ultrasound microscopy. One year postoperatively, UCVA decreased to 20/400, and BSCVA decreased to 20/60 with refraction of -4.50 +5.00 x 90 degrees. The patient was intolerant of contact lens wear and is considering collagen cross-linking, Intacs, or corneal transplantation. CONCLUSIONS: Ectasia can occur more than 4 years after LASIK. Its etiology is unknown and management is challenging.     

Differences between regressive eyes and non-regressive eyes after LASIK for myopia in the time course of corneal changes assessed with the Orbscan

The aim of this study was to compare regressive eyes with non-regressive eyes after laser in situ keratomileusis (LASIK) for myopia with regard to the time course of biomechanical changes of the cornea and to evaluate the possible roles of these changes in refractive regression following surgery. 15 eyes of 9 patients with refractive regression and 15 eyes of 11 patients with no refractive regression after LASIK for myopia were enrolled in this study. The time courses of central corneal thickness (CCT) and anterior/posterior corneal curvature radiuses (CCR) were measured with Orbscan slit scanning before and 1 week, 1 month and 3 months after LASIK for myopia. The regressive and non-regressive eyes had similar time courses of CCT before and after LASIK, whereas the 2 groups differed in the time courses of corneal shifting movements. In the regression group, the posterior CCR after LASIK was relatively stable (all p > 0.05). By contrast, in the non-regression group, the postoperative posterior CCR at week 1 had a significantly steeper curvature than that at month 3 (p = 0.000). The anterior CCR in the regression group at week 1 had a significantly flatter curvature than that at month 3 (p = 0.002) postoperatively. In contrast, there was no significant change of anterior CCR postoperatively (all p > 0.05) in the non-regression group. Taken together, these data suggest that refractive regression after LASIK might be mainly induced by corneal protrusion rather than central corneal thickening.     

Changes in the posterior cornea after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To study the changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) using Scheimpflug topography with the Pentacam anterior segment imaging system (Oculus, Inc.). SETTING: Department of Ophthalmology, Albany Medical Center, and a private clinical practice, Albany, New York, USA. METHODS: In this prospective study, 121 consecutive myopic eyes (103 LASIK and 18 PRK) were evaluated preoperatively and postoperatively with the Pentacam to determine elevation changes in the posterior corneal surface. Changes in posterior elevation were calculated by comparing the best-fit sphere preoperatively and postoperatively to a fixed reference sphere using the central 9.0 mm preoperative cornea. Statistical and graphic analyses were performed. RESULTS: The 103 LASIK eyes had a mean correction of -3.76 diopters (D) and a mean ablation depth of 62.1 microm. The mean estimated residual bed thickness (RBT) (329 microm) demonstrated a mean posterior displacement of 2.64 +/- 4.95 microm. The 18 PRK eyes had a mean correction of -2.69 D and a mean ablation depth of 53.2 microm. The mean estimated RBT (464 microm) had a mean posterior displacement of -0.88 +/- 4.64 microm. The difference in the mean posterior corneal displacement between the LASIK and the PRK eyes was not statistically significant (P>.05, Student t test). CONCLUSIONS: There was no statistically significant difference in posterior corneal displacement between the LASIK and PRK patients. The changes in PRK and LASIK eyes appeared to be within acceptable measurement variation. Contrary to previous reports, ectatic changes to the posterior corneal surface did not routinely occur after LASIK surgery.     

准分子激光原位角膜磨镶术后5年的疗效观察

目的 观察近视眼患者准分子激光原位角膜磨镶术（laser in keratomileusis, LASIK）后5年中央角膜厚度及角膜曲率等的变化情况,并分析LASIK的安全性和远期疗效.方法 接受LASIK手术的近视患者52例（104只眼）,检查患者术后5年的视力、屈光状态、中央角膜厚度及角膜曲率,并与术前及术后早期数据进行比较.结果 术后5年均未发生继发性角膜扩张或医源性圆锥角膜;最佳矫正视力均无下降;平均等效球镜度数为（0.043±0.502）D,其中94眼为0～0.50 D,占90.38%.术后各阶段视力较稳定,等效球镜度数3个月时渐趋稳定.术后1年与术后5年中央角膜厚度差异无统计学意义（P〉0.05）,而各自与术后预计角膜厚度相比差异有统计学意义（P〈0.05）,均较术后预计角膜厚度厚;术后1～5年角膜曲率差异无统计学意义（P〉0.05）.结论 LASIK治疗近视具有良好的预测性和稳定的远期疗效.     

Early spatial changes in the posterior corneal surface after laser in situ keratomileusis

PURPOSE: To evaluate the forward shift of the posterior corneal surface after myopic laser in situ keratomileusis (LASIK) relative to the residual stromal bed thickness and the ablation percentage of the total corneal thickness. SETTING: Department of Ophthalmology, Ilsan Paik Hospital, Inje University, Ilsan, Korea. METHODS: Three hundred sixty-three eyes of 182 consecutive patients who had LASIK were examined retrospectively. The range of the refractive errors was -1.5 to -12.0 diopters. Corneal topography using Orbscan II (Bausch & Lomb) and pachymetry were obtained preoperatively and 1 week and 1, 2, and 3 months postoperatively. The patients were divided into 4 groups based on the residual stromal bed thickness: Group 1, 145 eyes with less than 250 microm; Group 2, 129 eyes with 250 to 300 microm; Group 3, 76 eyes with 300 to 350 microm; and Group 4, 13 eyes with more than 350 microm. They were also grouped by the ablation percentage per total corneal thickness: Group A, 16 eyes with less than 10%; Group B, 166 eyes with 10% to 20%; Group C, 146 eyes with 20% to 30%; and Group D, 35 eyes with more than 30%. RESULTS: The increase in the forward shift of the posterior corneal surface postoperatively correlated with the residual corneal bed thickness and the ablation ratio per total corneal thickness. There were no statistically significant changes in the postsurgical forward shift of the posterior corneal surface if the residual corneal thickness remained greater than 350 microm or the ablation percentage was less than 10%. CONCLUSIONS: Increased forward shift of the posterior corneal surface is common after myopic LASIK and correlates with the residual corneal thickness and the ablation percentage per total corneal thickness. An excessively thin residual corneal bed or a large ablation percentage may increase the risk of iatrogenic complications.     

Residual bed thickness and corneal forward shift after laser in situ keratomileusis

PURPOSE: To prospectively assess the forward shift of the cornea after laser in situ keratomileusis (LASIK) in relation to the residual corneal bed thickness. SETTING: Miyata Eye Hospital, Miyazaki, Japan. METHODS: Laser in situ keratomileusis was performed in 164 eyes of 85 patients with a mean myopic refractive error of -5.6 diopters (D) +/- 2.8 (SD) (range -1.25 to -14.5 D). Corneal topography of the posterior corneal surface was obtained using a scanning-slit topography system before and 1 month after surgery. Similar measurements were performed in 20 eyes of 10 normal subjects at an interval of 1 month. The amount of anteroposterior movement of the posterior corneal surface was determined. Multiple regression analysis was used to assess the factors that affected the forward shift of the corneal back surface. RESULTS: The mean residual corneal bed thickness after laser ablation was 388.0 +/- 35.9 microm (range 308 to 489 microm). After surgery, the posterior corneal surface showed a mean forward shift of 46.4 +/- 27.9 microm, which was significantly larger than the absolute difference of 2 measurements obtained in normal subjects, 2.6 +/- 5.7 microm (P<.0001, Student t test). Variables relevant to the forward shift of the corneal posterior surface were, in order of magnitude of influence, the amount of laser ablation (partial regression coefficient B = 0.736, P<.0001) and the preoperative corneal thickness (B = -0.198, P<.0001). The residual corneal bed thickness was not relevant to the forward shift of the cornea. CONCLUSIONS: Even if a residual corneal bed of 300 microm or thicker is preserved, anterior bulging of the cornea after LASIK can occur. Eyes with thin corneas and high myopia requiring greater laser ablation are more predisposed to an anterior shift of the cornea.     

Keratectasia after laser in situ keratomileusis (LASIK): evaluation of the calculated residual stromal bed thickness

PURPOSE: To report corneal histopathology associated with keratectasia after laser in situ keratomileusis (LASIK) and to evaluate the thickness of the calculated residual stromal bed in two cases and those in the literature. DESIGN: Interventional case reports. METHODS: Three eyes of two patients developed keratectasia after LASIK. Corneal specimens after penetrating keratoplasty in one eye of each patient were studied histopathologically, and the residual stromal bed was directly measured. For comparison, residual stromal bed thicknesses were calculated from published cases of keratectasia. RESULTS: Two eyes of a 26-year-old woman and one eye of a 22-year-old woman developed keratectasia after LASIK. Calculated residual stromal bed thicknesses were 210, 213, and 261 microm. Histologic sections revealed focal scarring in the flap plane. The cornea specimens measured 75 and 118 microm thinner than calculated values immediately after LASIK. Transmission electron microscopy of one case revealed an average lamellar thickness of 0.94 microm. In 28 (49%) of 57 previous cases of keratectasia, the calculated residual stromal bed thicknesses were greater than 250 microm. CONCLUSIONS: Both the flap and the stromal bed of the cornea may thin after LASIK. A residual stromal bed thickness of 250 microm does not preclude the development of keratectasia after LASIK.     

Evaluation of apparent ectasia of the posterior surface of the cornea after keratorefractive surgery

PURPOSE: To calculate the apparent posterior corneal changes after keratorefractive surgery and reevaluate corneal ectasia displayed by Orbscan (Orbtek). SETTING: Department of Ophthalmology, Nara Medical University, Nara, Japan. METHODS: Postoperative:preoperative magnification ratio of the posterior surface of the cornea was calculated in a theoretical eye model. RESULTS: Assuming the preoperative corneal thickness is 600.00 microm, the preoperative refractive power of the anterior corneal surface is 48.0 diopters (D), the refractive power of the cornea is 1.376, the ablation diameter is 6.0 mm, the postoperative corneal thickness is 480.00 microm, the postoperative refractive power of the anterior corneal surface is 38.0 D, and the posterior surface of the cornea does not change postoperatively, the apparent image of the posterior surface of the cornea becomes 0.778% smaller postoperatively. If the posterior radius of curvature of the cornea is 6.2 mm, it becomes smaller by 48.24 microm. If this change directly affects the difference map, the posterior surface of the cornea moves forward by 48.24 microm. CONCLUSION: The results correspond to the amount of ectasia in previous reports. This artifact may explain the apparent ectasia detected by Orbscan.