角膜厚度和角膜曲率对LASIK术后眼压测量值的影响

目的探讨准分子激光原位角膜磨镶术（LASIK）后角膜厚度和角膜曲率对眼压测量值的影响。方法150例（285眼）近视行LASIK并随访1年，对手术前后的角膜厚度、角膜曲率及眼压进行统计学分析。结果LASIK术后3、6、12个月的角膜厚度、角膜曲率及眼压测量值均较术前明显下降（P〈0．01）。术前及术后3、6、12个月的眼压测量值与角膜厚度、角膜曲率呈正相关。结论LASIK术后眼压测量值低于术前，眼压测量值与角膜厚度和角膜曲率均呈正相关，角膜厚度和角膜曲率是眼压测量值的影响因素。     

准分子激光原位角膜磨镶手术前后眼压测量值的多因素分析

目的通过对准分子激光原位角膜磨镶手术(LASIK)前后眼压变化的多因素分析,指导临床对眼压测量值进行正确评估。方法LASIK手术患者按屈光度分4组,每组随机选择患者50只眼,采用非接触式眼压计测量手术前后眼压,同时测角膜中央厚度、角膜曲率及屈光度,将所得数据应用统计学方法处理,分析影响眼压的因素。结果200例患者术前眼压值范围为(14.33±2.99)mmHg(9～22 mmHg),术后眼压值范围为(9.94±1.24)mmHg(8～14 mmHg),非接触式眼压与角膜中央厚度、屈光度呈正相关,与性别相关,与年龄无关(r=0.653,P<0.001;r=0.548,P<0.001;r=-0.159,P<0.01;r=-0.072,P=0.167),角膜曲率<42.0 D时与眼压呈正相关(r=0.422,P<0.001)。建立多元线性回归方程:Y=-3.571 0.034×角膜厚度(μm) A×角膜曲率(D) 0.199×屈光度(D)-0.58×性别(P<0.001,角膜曲率<42.0 D时A=0.021;角膜曲率≥42.0 D时,A= 0,性别:1=男性,2=女性)。结论影响LASIK患者手术前眼压计测量值的主要因素是角膜中央厚度、屈光度和性别,而对LASIK术后患者需同时考虑角膜曲率,在临床诊断时应考虑到以上影响因素,对眼压测量值进行修正,以免造成误诊及漏诊。     

LASIK术后角膜基质床厚度影响因素的析因设计研究

目的:采用析因设计法探讨LASIK术角膜基质床厚度的主要影响因素间的关联及实用性。方法:选取眼科门诊接受LASIK术患者30例60眼,以术前眼压、屈光度、术后角膜基质床厚度为研究因素进行析因设计试验。结果:术前屈光度间、术前眼压与术前屈光度之间差异无统计学意义(P>0.05);术前眼压间(P<0.05)、术前眼压与术后角膜基质床厚度之间(P<0.01)及术前屈光度与术后角膜基质床厚度之间(P<0.01)差异有统计学意义。术前眼压、屈光度、术后角膜基质床厚度间存在交互影响(P<0.01)。结论:析因设计法可用于眼科专业中多因素多水平的研究;术前眼压、屈光度、术后角膜基质床厚度是影响LASIK术成功与否的重要因素,在术前眼压<21mmHg、术前屈光度中度、术后角膜基质床厚度保留300μm以上较安全。     

LASIK术后非接触性眼压测定值的改变

目的:研究准分子激光原位角膜磨削术(laser·in situ keratomileusis,LASIK)术后非接触性眼压计(noncontact tonometer,NCT)测量值的准确性。方法:对180例(256只眼)近视患者行IASIK手术,手术前、后采用NCT测量患者的眼压,并测量角膜厚度和角膜曲率,进行统计学分析。结果:LASIK术后NCT测量值明显低于术前,差异有显著性(P<0.001),术后一年眼压下降(6.54±2.1)mmHg(1 mmHg=0.133 kPa)。术后一年眼压下降值与角膜厚度减少及角膜前表面曲率的降低有关(P<0.01),建立二元回归方程如下:Y=0.355+0.0342X1+0.365X2。Y:术前术后眼压差(mmHg),x1:术前术后角膜曲率差(D),x2:角膜切削厚度(μm)结论:LASIK术后NCT眼压测量值明显低于术前,术后所测量眼压与角膜切削厚度、角膜曲率有关。     

动态轮廓眼压计与非接触式眼压计的比较

目的探讨中央角膜厚度和角膜曲率对轮廓动态眼压计以及非接触式眼压计眼压测量结果的影响。方法接受准分子激光原位角膜磨镶术(LASIK)的近视患者27例(54只眼),分别于术前和术后第4周使用非接触式眼压计(NCT)和动态轮廓眼压计(DCT)进行眼压测量。多元线性相关分析研究NCT、DCT测量值和角膜曲率及角膜中央厚度(CCT)之间的相关性。结果LASIK术后NCT测量值降低,而DCT测量值和术前比较差异则无统计学意义。角膜曲率、CCT和NCT读数呈线性相关,而与DCT读数无关。结论DCT测量眼压不受角膜曲率和中央角膜厚度影响,因此更适合于正常眼以及曾经接受角膜屈光手术眼的眼压测量。     

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。     

PRK、LASIK术后非接触眼压测量值的准确性

目的 :评估准分子激光屈光性角膜切削术 (PRK)和准分子激光原位角膜磨镶术 (LASIK)后非接触眼压 (NCT)测量值的准确性。方法 :对 5 5例 (10 9只眼 )行PRK和 5 7例(113只眼 )行LASIK的近视患者进行回顾性分析 ,手术前、后采用非接触眼压计测量患者的眼压 ,并测量角膜厚度和角膜曲率 ,进行统计学分析。术后随访时间 >1年 ,停用激素至少半年以上。结果 :PRK和LASIK术后NCT测量值都低于术前 ,分别下降 (3.6 7± 1.6 5 )mmHg和 (5 .11± 1.5 1)mmHg ,差异有非常显著意义 (P <0 .0 0 1)。PRK和LASIK术前眼压测量值与角膜厚度均呈高度正相关 (P <0 .0 0 1) ;术后眼压测量值的降低与角膜厚度的减少高度正相关 (P <0 .0 5 ) ,其回归方程分别为 ^Y(手术前、后眼压差 ,mmHg) =1.36 1+0 .0 38X(手术前、后角膜厚度差 ,μm)和 ^Y =1.95 4 +0 .0 4 0X ;眼压测量下降值和角膜曲率的降低无关。结论 :PRK和LASIK术后眼压测量值均低于术前 ,角膜厚度是导致手术后眼压测量值减少的主要因素 ,且眼压测量值随角膜厚度的减少而下降。在临床工作中 ,应避免术后类固醇性青光眼因眼压测量值的下降而被漏诊。     

LASIK前后非接触性眼压测定值的分析

目的：探讨准分子激光原位角膜磨镶术（LASIK）手术前后非接触眼压计（NCT）测量值的变化及其屈光度矫正值和术中角膜切削厚度之间的关系。方法：LASIK392眼按等效球镜分为A,B,C,D4组,对术前术后的NCT测量值进行统计学分析,并对眼压改变值与预屈光度矫正值和术中角膜切削厚度作相关性分析。结果：⑴各组术前NCT测量值的改变无显著性差异（P＞0.05);⑵各组术前术后NCT测量值的改变差异有显著性意义（P＜0.01);⑶术后预屈光度矫正值与眼压下降值呈正相关关系。结论：为了避免延误LASIK术后青光眼的诊断,不能按传统的正常眼压值衡量术后结果。LASIK术后角膜厚度变薄是导致术后NCT测量值下降的直接原因。     

近视眼激光原位角膜磨镶术后眼压变化及真实眼压评估

目的 研究近视眼激光原位角膜磨镶术（LASIK）后的眼压变化并建立一个真实眼压估计的统计模型。方法 分别对47例（93眼）接受LASIK手术近视眼患者在术前和术后至少6月以上用非接触气动眼压计进行眼压测量,同时测量手术前后的中央角膜厚度和中央角膜曲率,比较手术前后的眼压变化,并利用术后眼压以及中央角膜厚度和角膜曲率的变化通过多变量线性回归法建立一个估计真实眼压的模型。结果 术后眼压测量值比术前下降（5.65±1.71）mmHg,差异有显著性,t=8.65,P=0.00。术前眼压（代表真实眼压）与术后眼压、术前后中央角膜厚度下降率和中央角膜曲率差显著相关,P=0.00,R2=0.73。结论 近视眼LASIK术后眼压测量值偏低,尽管可以利用术后眼压和角膜厚度及曲率的变化建立一个估计真实眼压的统计模型,但其它的相关影响因素仍需要进一步了解。     

动态轮廓眼压计与压平眼压计的比较

目的:评价和比较动态轮廓眼压计和Goldmann压平眼压计测得的LASIK手术后眼压值。方法:接受准分子激光原位角膜磨镶术(LASIK)的近视患者34例68眼,分别于术前和术后3mo使用动态轮廓眼压计(Pascal dynamic contour tonometer,PDCT)和Goldmann压平眼压计(the Goldmann applanation tonometer,GAT)进行眼压测量。比较手术前后两种测量方法测得的眼压值的差异。多元线性相关分析研究GAT,PDCT测量值和角膜曲率及角膜中央厚度(CCT)之间的相关性。结果:LASIK手术后GAT测量值较术前低,而PDCT值和术前比较差异则无统计学意义。角膜曲率、CCT和GAT读数呈线性相关,而与PDCT读数无关。结论:GAT测量得到的眼压低于实际值。PDCT测眼压不受角膜曲率和中央角膜厚度影响。     

Changes in corneal thickness and curvature after different excimer laser photorefractive procedures and their impact on intraocular pressure measurements

Background Excimer laser refractive surgery alters the shape and thickness of the cornea by removing central corneal tissue with submicrometer precision. The aim of the study was to analyze the changes in central corneal thickness (CCT) and curvature before and after different excimer laser photorefractive procedures and their possible impact on intraocular pressure (IOP) estimations with Goldmann applanation tonometry. Methods Data on CCT, corneal curvature and IOP readings with Goldmann applanation tonometry before and after excimer laser photorefractive surgery were analyzed retrospectively. The data was further analyzed separately in two subgroups; the photorefractive keratectomy /laser-assisted subepithelial keratomileusis (PRK/LASEK) group and the laser in situ keratomileusis (LASIK) group. Results The overall post-operative IOP readings were significantly lower than pre-operative values. There was a significant difference in the lowering of the IOP readings between the two subgroups: LASIK caused a lower IOP reading than PRK/LASEK. Conclusion The change in corneal thickness and curvature affects the estimation of IOP with Goldmann applanation tonometry after excimer laser photorefractive surgery. The amount of reduction in IOP reading might be influenced by the specific laser surgical procedure. This is of clinical importance in the evaluation of any future glaucoma in the increasing number of patients who undergo photorefractive laser surgery.     

Effect of corneal curvature and corneal thickness on the assessment of intraocular pressure using noncontact tonometry in patients after myopic LASIK surgery

PURPOSE: To evaluate the effect of corneal curvature and corneal thickness on the assessment of intraocular pressure (IOP) using noncontact tonometry (NCT) in patients after myopic LASIK surgery. METHODS: All patients who had myopic LASIK in a university-based eye clinic between February 2002 and May 2002 were retrospectively analyzed. Preoperative NCT was compared with postoperative NCT, postoperative corneal thickness, and postoperative corneal curvature. RESULTS: The difference between the mean preoperative NCT (15.46 +/- 2.50 mm Hg) and postoperative NCT (6.30 +/- 1.57 mm Hg) was significant (9.16 +/- 1.96 mm Hg, P < 0.010). Preoperative NCT significantly correlated with postoperative NCT (P < 0.001), postoperative corneal thickness (P = 0.006), and postoperative anterior corneal curvature (P < 0.010). CONCLUSIONS: Both corneal thickness and anterior corneal curvature affect IOP assessment in patients with myopic LASIK. Although correction formulas can be used to estimate the actual IOP, alternative methods should be investigated to assess IOP independent of corneal thickness and curvature.     

Changes in intraocular pressure after laser in situ keratomileusis for myopia,hyperopia, and astigmatism

PURPOSE: Reports have shown that photorefractive keratectomy changes intraocular pressure (IOP) in myopic eyes by changing the thickness and curvature of the cornea. Changes in intraocular pressure after laser in situ keratomileusis (LASIK) for hyperopia led the authors to evaluate IOP after LASIK for various refractive errors. METHODS: The measurement of intraocular pressure with a Goldman applanometer in the central cornea was evaluated before and 3 months after LASIK in 100 eyes of 55 patients with various refractive errors. Corneal thickness (pachymetry) and corneal topography were evaluated. RESULTS: After LASIK, a significant decrease of intraocular pressure was observed in most eyes: mean 11.9 +/- 3.2 mmHg before and 9.8 +/- 2.6 mmHg at 3 months after surgery (P < .001). Mean decrease in IOP was 2.75 +/- 3.3 mmHg (P < .0001) for myopic eyes, 2.28 +/- 2.43 mmHg (P < .001) for hyperopic eyes, and 1.47 +/- 2.5 mmHg (P < .0012) for astigmatic eyes. IOP reduction was not significantly correlated to the amount of ablation (r = 0.05) or to corneal thickness. CONCLUSION: Intraocular pressure decreased in myopic, hyperopic, and astigmatic eyes after LASIK. The reduction was not correlated to the amount of tissue removed or to flattening or steepening of the central cornea.     

Applanation tonometry in "normal" patients and patients after LASIK

BACKGROUND: Until now it was thought that morphological parameters of the eye such as corneal thickness, corneal curvature and axial length do not affect tonometry results. However, the aim of this study was to find out whether there actually is an influence of these parameters on applanation tonometry. PATIENTS AND METHOD: In this prospective study we examined 125 eyes of 125 normal patients with a corneal thickness of 568.8 +/- 43.79 microm, a corneal curvature of 7.72 +/- 0.27 mm and an axial length of 23.62 +/- 2.05 mm. Before performing a phacoemulsification, the anterior chamber was temporarily punctured. With a closed system the intraocular pressure (IOP) was manometrically set at 20, 35 and 50 mmHg using an H (2)O column. The IOP was then measured with a Perkins tonometer. With these patients we compared 102 eyes that had undergone LASIK due to a myopia of 6.3 +/- 2.17 D. Before and 6 months after surgery, IOD, k-values and central corneal thickness of these patients were measured. RESULTS: At all set pressure levels there was a highly significant correlation of measured IOP and corneal thickness. At all set pressure levels the measured IOP significantly depended on corneal thickness (r(2) = 0.78 - 0.83). After LASIK, IOP was reduced from 16.5 +/- 2.1 to 12.9 +/- 1.9 mmHg. There was a significant correlation between IOP and corneal curvature as well as corneal thickness (r(2) = 0.631; P < 0.001). The biomechanical characteristics of the cornea are changed so that the measured IOP has to be corrected by an additional 0.75 mmHg. CONCLUSION: Since corneal thickness does affect Goldmann applanation tonometry we recommend to use the "Dresden Correction Table" (Tab. ) to achieve the real IOP. Pressure measurements after LASIK are inaccurate because of a change in corneal biomechanics, corneal thickness and curvature and they should be corrected as follows: IOP (real) = IOP (measured) + (540 - CCT)/71 + (43 - K-value)/2.7 + 0.75 mmHg.     

Measurement of intraocular pressure in LASIK and LASEK patients using the Reichert Ocular Response Analyzer and Goldmann applanation tonometry

PURPOSE: To determine the efficacy of the Reichert Ocular Response Analyzer (ORA) to measure intraocular pressure (IOP) following corneal laser refractive surgery. METHODS: Intraocular pressure was measured using Goldmann applanation tonometry preoperatively and 3 months following LASIK and LASEK for all levels of myopia and low levels of hyperopia. In LASIK eyes, 120-microm flaps were cut using the Hansatome XP. The ORA was used to measure Goldmann correlated IOP and corneal compensated IOP 3 months postoperatively. Postoperative central corneal thickness, hysteresis, and corneal curvature were assessed to determine their relationship with postoperative change in Goldmann applanation tonometry IOP. Efficacy of ORA IOP measurement was analyzed by comparing Goldmann applanation tonometry IOP with Goldmann correlated IOP. RESULTS: LASEK was performed on 35 eyes, and LASIK was performed on 90 eyes. In the LASIK group, mean Goldmann applanation tonometry IOP decreased 3.7+/-2.3 mmHg postoperatively (P=.00). Postoperative Goldmann applanation tonometry did not differ significantly (P=.06) from postoperative ORA Goldmann correlated IOP (10.2+/-2.1 mmHg). In the LASEK group, mean Goldmann applanation tonometry IOP decreased 3.9+/-2.3 mmHg (P=.00). Postoperative Goldmann applanation tonometry did not differ significantly (P=.6) from postoperative ORA Goldmann correlated IOP (10.7+/-2.5 mmHg). Postoperative decrease in Goldmann applanation tonometry IOP did not correlate with age, ablation depth, pre- and postoperative central corneal thickness or corneal hysteresis, or postoperative decrease in corneal curvature. CONCLUSIONS: Intraocular pressure measurements were similar using both the ORA Goldmann correlated IOP and Goldmann applanation tonometry following keratorefractive surgery.     

Effects of antiglaucoma drugs on refractive outcomes in eyes with myopic regression after laser in situ keratomileusis

PURPOSE: To assess effects of antiglaucoma drugs on refractive outcomes in eyes with myopic regression after laser in situ keratomileusis (LASIK). DESIGN: Prospective, nonrandomized clinical trial. METHODS: We examined 27 eyes with mean myopic regression +/- standard deviation of -1.26 +/- 0.48 diopters (D; range, -0.50 to -2.25 D) after LASIK. Nipradilol 2.5% was administered topically twice daily to these regressive eyes. We obtained the refraction (spherical equivalent, astigmatism), intraocular pressure (IOP) measurements, pachymetry, geometry, and refractive power of the cornea before and three months after treatment. RESULTS: Mean manifest refraction was improved significantly from -1.02 +/- 0.52 D to -0.44 +/- 0.39 D (P < .001). However, mean manifest astigmatism was changed from -0.55 +/- 0.30 D to -0.49 +/- 0.22 D, but the difference was not significant (P = .23). The IOP was decreased significantly from 11.4 +/- 2.4 mm Hg to 9.4 +/- 1.3 mm Hg (P < .001). Central corneal thickness was not changed significantly from 505.2 +/- 39.3 microm to 503.6 +/- 38.7 microm (P = .61). The posterior corneal surface was shifted posteriorly by 9.1 +/- 8.2 microm, and the total refractive power of the cornea was decreased significantly, by 0.63 +/- 0.62 D (P < .001), at three months after application. CONCLUSIONS: The preliminary data show that antiglaucoma drugs are effective for the reduction of the refractive regression, especially of the spherical errors, after LASIK. It is suggested that backward movement of the cornea may occur, possibly flattening the corneal curvature by lowering the IOP. Reduction of the IOP may contribute to improving regression after keratorefractive surgery.     

Corneal power, thickness, and stiffness: results of a prospective randomized controlled trial of PRK and LASIK for myopia

PURPOSE: To compare the short-, medium-, and long-term changes in corneal optical power and corneal aberrations, central corneal thickness, and corneal "stiffness" assessed by pneumotonometry readings in patients having laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) for myopia. SETTING: Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark. METHODS: One eye of each of 45 patients with myopia ranging from -6.00 to -8.00 diopters (D) (spherical equivalent spectacle refraction [SER]) was randomized to LASIK (n=25; mean SER -7.12 D +/- 0.57 [SD]) or PRK (n=20; mean SER -6.91 +/- 0.57 D). Data were collected prospectively before and 1, 3, 6, 12, and 36 months after surgery. Measurements included corneal topography (TMS-1, Tomey), corneal thickness (ultrasound pachymetry), and apparent intraocular pressure (IOP) (pneumotonometry). Retreatments were not performed during the first year, and retreated eyes were excluded from the 3-year follow-up. Changes in corneal power and aberrations, thickness, and apparent IOP were calculated in a pair-wise manner for 3 time periods: short term (preoperative to 1 month after surgery), medium term (1 to 12 months after surgery), and long term (1 to 3 years after surgery). RESULTS: In the short term, corneal power decreased equally in LASIK and PRK eyes. Spherical aberrations and coma-like aberrations increased equally, while corneal thickness decreased significantly less in LASIK eyes than in PRK eyes. The apparent IOP decreased more in LASIK eyes than in PRK eyes. In the medium term, corneal power increased significantly in both groups. Spherical aberrations decreased significantly in PRK eyes but not in LASIK eyes. From 1 to 12 months, corneal thickness increased more in PRK eyes than in LASIK eyes. During this period, the apparent IOP increased significantly in LASIK eyes. In the long term, corneal power and corneal aberrations did not change significantly in either group. Corneal thickness increased slightly but significantly in both groups. The apparent IOP increased significantly more in PRK eyes. CONCLUSIONS: Differences between LASIK and PRK related to time-dependent events affecting corneal shape and structural integrity were present. Peripheral changes in flap hydration in LASIK eyes and epithelial and/or stromal thickening in PRK eyes appeared to be the most important factors in optical power changes in the first year after treatment. The changes in apparent IOP suggest that some interlamellar healing occurred during the first year after LASIK. After LASIK and PRK, corneal bending stiffness seemed permanently decreased, although some restiffening may occur in PRK eyes in the long term.     

Underestimation of intraocular pressure in eyes after laser in situ keratomileusis

PURPOSE: Retrospectively, we reviewed the records of 65 patients (115 eyes) regarding the intraocular pressure (IOP) after laser in situ keratomileusis (LASIK). METHODS: The mean patient age was 31.2 +/- 10.5 years. The average preoperative spherical equivalent was -6.85 +/- 2.54 diopters. A noncontact pneumatic tonometer and a Goldmann applanation tonometer were used in measuring the IOP. RESULTS: The IOP after LASIK was significantly lower than that before surgery (Mann-Whitney U-test). The IOP correlated significantly with the corrected diopter value, corneal thickness, and corneal curvature (Spearman rank correlation). CONCLUSIONS: The postoperative IOP can be underestimated due to decreased corneal thickness and curvature. When evaluating IOP after LASIK surgery, this possibility should be carefully investigated.