Pentacam和Sirius地形图系统与超声测厚仪角膜厚度的对比研究

目的:探讨Sirius与Pentacam及超声测厚仪测量中央角膜厚度的一致性.方法:对51例102眼正常人采用Pentacam和Sirius及超声角膜测厚仪三种仪器测量角膜厚度,记录并比较三种方法测量所得中央角膜厚度结果,同时运用Bland-Altman法绘制图表分析两两间一致性.结果:A超中央角膜厚度平均值低于 Pentacam的平均值,Sirius中央角膜厚度的平均值最接近A超平均值.Sirius与Pentacam一致性的比较:其Bland-Altman图中3.92%的点在95%一致性界限以外.在一致性界限以内,Sirius与Pentacam中央角膜厚度差值的绝对值最大为19.5μm.Sirius与A超一致性的比较:其Bland-Altman图中2.94%的点在95%一致性界限以外.在一致性界限以内,Sirius与A超中央角膜厚度差值的绝对值最大为18.667μm.Pentacam与A超一致性的比较:其Bland-Altman图中5 82%点在95%一致性界限以外.在一致性界限以内,Pentacam与A超中央角膜厚度差值的绝对值最大为25 33μm.结论:Sirius系统与Pentacam系统具有良好的一致性,且Sirius系统比Pentacam系统更接近A超角膜测厚的结果.     

Repeatability and agreement of central corneal thickness measurements with a new handheld non-contact pachymeter

Purpose

To compare the repeatability of central corneal thickness (CCT) measurements taken with a new handheld pachymeter (Occuity PM1 pachymeter) and to assess its agreement with ultrasound biometry and two commercially available optical biometers in participants with normal eyes.

Methods

Three consecutive CCT measurements of the right eye of 105 participants with normal corneas were acquired by the PM1 pachymeter, Lenstar LS 900 and Oculus Pentacam HR in a random order. This was followed by three measurements with a handheld ultrasound pachymeter (UP) (Pachmate 2). Repeatability and the repeatability limit were calculated for each device and Bland–Altman limits of agreement (LoA) were determined for the PM1 pachymeter compared to the other devices.

Results

The mean CCT (±SD) was 551.04 ± 33.43, 558.62 ± 31.46, 549.41 ± 31.00 and 539.73 ± 29.50 μm for the PM1 pachymeter, UP, Lenstar and Pentacam, respectively. The repeatability limits (expressed as the within subject SD for repeat measurements) were 14.02, 13.68, 4.99 and 9.90 μm, respectively. The closest agreement was between the PM1 and Lenstar (mean difference = −1.63 μm with LoA 10.72 μm below and 13.97 μm above the readings obtained with the Lenstar). The PM1 underestimated CCT compared to UP (mean difference = 7.58 μm, LoA 24.63 μm below and 9.47 μm above UP). The agreement was lowest between the PM1 and Pentacam (mean difference = −11.30 μm, LoA between 4.29 and 26.89 μm).

Conclusions

The PM1 pachymeter shows excellent precision for CCT measurements across a range of corneal thicknesses in normal eyes and provides a safe and easy-to-use alternative to ultrasound pachymetry.     

Orbscan—II、Pentacam及超声测厚仪角膜厚度测量值的比较

目的探讨Orbscan-II、Pentacam及超声角膜测厚仪三种仪器测量角膜中央厚度的差异及其临床意义。方法对预行准分子激光角膜手术的近视患者159例（318眼）,采用0rbscan—II、Pentacam及超声角膜测厚仪三种仪器测量角膜中央厚度,并对测量结果进行统计学分析。再根据超声角膜测厚仪所测得的角膜厚度进一步将患者分为三组（〈500um组、500～570um组和≥570um组）,在每个组中对三种方法所测得的结果进行统计学分析。结果Orbscan-II、Pentacam、超声角膜测厚仪测得的角膜中央厚度平均值分别为（527．9±43．0）um、（526．3±38．4）um、（522．6±37．8）um。经方差分析,三者差异无统计学意义（F=1．491,P=0．226）。分组后,角膜厚度〈500um和500—570um组,三种方法所得数据差异无统计学意义（F=1．546,P=0．215;F=2．107,P=0．123）;而≥570um组,三种方法测量结果差异存在统计学意义（F=5．396,P=0．006）,进一步采用Bonferroni检验分析组间差异,Orbcan—II组测量值明显高于Pentacam组（P=0．029）和超声测厚仪组（P=0．010）,Pentacam组和超声测厚仪组之间无差异（P〉0．05）。结论三种方法用于测量准分子激光角膜手术前近视患者的角膜中央厚度时虽然存在一定差异,但总体上无统计学意义,具有很好的协同性,但相互间还不能完全替代。     

Pentacam分析仪测量近视眼患者角膜厚度及影响因素分析

目的使用Pentacam眼前节分析系统测量近视患者角膜中央最薄点厚度,并探讨与A型超声角膜测厚仪测量结果的差异及可能影响因素。方法对预行准分子激光角膜手术的近视患者150例(300眼),分别采用Pentacam系统及A型超声角膜测厚仪测量角膜中央最薄点厚度,对测量结果进行统计学分析。结果 Pentacam、A型超声角膜测厚仪测得的中央角膜最薄点厚度平均值分别为(543.7±26.3)μm、(539.2±27.4)μm,二者高度相关(r=0.97,P=0.0001)。Pentacam测得角膜厚度值偏厚,二者差值平均(4.4±7.0)μm,差异有统计学意义(t=10.94,P=0.0001),该差值与A型超声测量角膜厚度值、年龄有关(P=0.0001),而与屈光度、性别、角膜直径、角膜曲率等无关。结论 Pentacam测量近视患者角膜厚度值略高于A型超声角膜测厚仪,尽管二者有很好的协同性,但相互间还不能完全替代。     

不同测厚仪角膜厚度测量值的对比研究

目的：探讨超声及Schempflug原理测量中央角膜厚度(CCT)的差异及其临床意义。

方法：对2011-07我院门诊角膜正常的患者86例150眼分别用非接触式眼压/角膜厚度测量仪NT-530P和Pentacam眼前段分析仪、超声角膜测厚仪三种仪器测量CCT。用SPSS 17.0统计学软件对不同方法测量的结果进行单因素方差分析和Pearson相关性分析,并绘制Bland-Altman散点图,分析不同测量方法之间的一致性。

结果：三种仪器所测得CCT测量结果分别为：NT-530P 541.19±32.47μm,Pentacam 542.76±32.40μm,超声角膜测厚仪539.88±31.98μm。三种检查仪测量结果差异无统计学意义(F=0.290,P=0.748),且两两之间高度相关(r₁=0.954, r₂=0.973, r₃=0.948)。以A超角膜测厚仪测量的CCT为基准把患者分为3组：CCT≤520μm,520μm570μm,对三种仪器测量的结果进一步对比分析,三组中的各仪器测量结果均无统计学差异(P>0.05)。

结论：三种方法测量的CCT差异无统计学意义(P>0.05),且具有很好的相关性。     

Pentacam系统与A超角膜测厚仪测量中央角膜厚度的一致性和重复性

目的 探讨Pentacam三维眼前节分析诊断系统测量角膜厚度的可重复性,比较其结果与A型超声角膜测厚仪测量结果的一致性。方法 112例拟行准分子激光角膜屈光手术的受检者,只选取右眼作为研究对象,分别由两位检查者肓法使用Pentacam系统和A超角膜测厚仪测量中央角膜厚度3次,将结果进行对比分析。角膜厚度值的比较采用配对t检验进行统计学分析;一致性检验采用Bland-Altman法。结果 角膜厚度均值分别为Pentacam系统(538.63±31.55) μm,超声测厚仪(541.02±30.45) μm,两者差异具有统计学意义（t=- 3.414,P=0.001）,两者的差值平均为（-2.39±7.42）μm。两法具有较好的一致性,95％的一致性界限为（- 16.93 μm,12.15 μm）。Pentacam系统与超声测厚仪测量值的组内相关系数分别为0.86和0.88,两种仪器的测量结果都比较稳定、重复性好。结论 Pentacam系统与超声测厚法具有较好的一致性,测量结果的重复性也较好,但要注意增加测量次数。     

Reproducibility and repeatability of central corneal thickness measurement in keratoconus using the rotating Scheimpflug camera and ultrasound pachymetry

PURPOSE: To assess repeatability, reproducibility, and agreement of rotating Scheimpflug camera (Pentacam Oculus, Wetzlar, Germany) and ultrasound pachymetry in measuring central thickness of keratoconic corneas. DESIGN: Method-comparison study. METHODS: In 33 patients with keratoconus (one eye per patient), two examiners each used both pachymetric methods to measure central corneal thickness (CCT); in the same session, measurements then were repeated by examiner 1 (A.M.). The difference between two examiners, and between first and second measurements by examiner 1, with both methods and the difference between the two pachymetric methods in measuring central thickness of keratoconic corneas were noted. RESULTS: With the rotating Scheimpflug camera, interexaminer correlation was higher (intra-class correlation coefficient [ICC], 0.98 vs 0.76) and inter-examiner variability was lower (95% limits of agreement [95% LoA], -14.8 to 13.8 microm vs -18.0 to +49.5 microm) than with ultrasound pachymetry. Both methods showed close first- to second-measurement correlation (ICC, > 90), but the rotating Scheimpflug camera had lower variability (95% LoA, -14.5 to 14.2 microm vs -27.4 to 26.0 microm). Mean CCT was 478.9 +/- 34.6 microm with the rotating Scheimpflug camera and 486.6 +/- 30 microm with ultrasound pachymetry. Although the mean difference was small (-7.8 microm), the 95% LoA (-43.8 to 28.2 microm) showed that the difference between the two methods can be considerable. CONCLUSIONS: In keratoconic corneas, the rotating Scheimpflug camera provides measurements of central thickness that are more reproducible and repeatable than those obtained with ultrasound pachymetry. The rotating Scheimpflug camera seems to be suitable for disease staging and follow-up, when corneal thickness measurements may be repeated over time by different examiners.     

Central corneal thickness in patients with meibomian gland dysfunctiona

Purpose: The aim was to evaluate central corneal thickness in patients with meibomian gland dysfunction. Methods: The study group was made up of 40 eyes of 20 patients with meibomian gland dysfunction (mean age, 40.55 ± 10.7 years). Forty eyes of 20 healthy individuals (mean age, 39.25 ± 11.1 years) without any ophthalmic or systemic pathology were used as a control group. The central corneal thickness was measured with ultrasonic pachymetry. Results: The mean central corneal thickness was 541.45 ± 24.68 µm in the study group and 544.30 ± 22.16 µm in the control group. There was no statistically significant difference in the mean central corneal thickness measurements in the meibomian gland dysfunction group in comparison with the control group (p > 0.05). Conclusion: Central corneal thickness measurements do not differ in patients with meibomian gland dysfunction compared with healthy control subjects.     

Pentacam pachometry: comparison with non‐contact specular microscopy on the central cornea and inter‐session repeatability on the peripheral cornea

Purpose: Our aim was to compare specular microscopy (SM) and a new corneal topographer with rotating Scheimpflug camera (Pentacam) for non‐contact pachometry of the central cornea. The repeatability of Pentacam for topographic pachometry was also studied. Methods: Thirty‐nine subjects were recruited and one eye was selected randomly for non‐contact pachometry by SM and by Pentacam, in random order. The corneal thickness (CT) was monitored at 30‐second intervals for 10 minutes. Baseline CT was defined as the average of all measurements taken over the 10 minutes. Subjects were required to return within one to two weeks for a second corneal evaluation by Pentacam. Comparisons were made on the central CT between the two devices and on the topographic CT from Pentacam between the two visits. Results: The spontaneous variation of central CT was similar for the two instruments. Central CT varied within ±2.3 µm during the 10 minutes. The 95% limits of agreement between SM and Pentacam were within ±15 µm for the central CT. The spontaneous variation of peripheral CT was within ±3.1 µm. There was no significant difference (p > 0.05) between the two visits on CT at different regions. Further analysis found that with Pentacam three measurements should be taken to obtain topographic CT measurement of one per cent precision. Conclusion: Non‐contact specular microscopy and Pentacam have good agreement for central CT measurement. Topographic pachometry from Pentacam requires three repeated measurements for one per cent precision.     

四种仪器测量中央角膜厚度的比较

目的 分析Orbscan Ⅱ、AS-OCT和Pentacam测量术前检查患者中央角膜厚度(CCT)同超声测厚仪的差异和一致性.方法 连续选取行术前检查的屈光不正患者90例(180只眼),对每位患者分别用超声测厚仪、Orbscan Ⅱ、AS-OCT和Pentacam四种仪器测量其CCT,数据统计分析采用了配对t检验、简单线性相关和Bland-Ahman分析.结果 超声测厚仪、Orbscan Ⅱ、AS-OCT和Pentacam测量CCT平均值分别为(542.1±30.4)μm、(541.1±37.1)μm、(530.3±29.3)μm和(544.9±28.7)μm.超声测厚仪和Orbscan Ⅱ之间的比较没有统计学意义(P>0.05).超声测厚仪和AS-OCT、Pentacam之间的差别分别为(11.7±8.9)μm(P<0.01)、(-2.8±11.0)μm(P<0.01).线性相关显示超声测厚仪和Orbscan Ⅱ、AS-OCT、Pentacam三者间分别存在正相关(P<0.01).Bland-Altman分析显示超声测厚仪与Orbscan Ⅱ、AS-OCT、Pentacam三者间有较好的一致性,95%一致性界限分别为-37.4～+39.3μm、-5.6～+29.1μm、-24.4～+18.8μm.结论 对于准分子激光术前患者角膜厚度的测量,三种方法同超声的一致性好,都可用来测量角膜厚度,其中Orbscan Ⅱ的测量值大小受其声速系数的影响、AS-OCT同超声的一致性最好、Pentacam的测量值同超声最接近.但完全替代使用还须慎重.     

Determining corneal power using Pentacam after myopic photorefractive keratectomy

Purpose: To assess the accuracy of Pentacam Scheimpflug camera for corneal power measurement in eyes with previous photorefractive keratectomy for myopia. Methods: In this comparative interventional case series, 35 eyes of 35 patients who had myopic photorefractive keratectomy were studied. Corneal power was measured by conventional topography and Pentacam Scheimpflug camera, and equivalent keratometry readings (EKR) in different central corneal rings (0.5 to 4.5 mm), true net power and simulated keratometry (K) measurements as well as those obtained using Shammas no‐history, Koch‐Maloney and Haigis methods were compared with clinical history method. Results: All corneal power measurements except for the topography simulated K and true net power values were statistically similar to the clinical history values. Simulated keratometry and 4.5‐mm EKR values were more closely correlated with clinical history method. Shammas formula, Pentacam simulated K and 3‐, 4‐ and 4.5‐mm EKR provided a 95% confidence interval within ±0.50 D of the mean clinical history method value, among these, the width of the 95% limits of agreement (LoA) was narrower for Shammas and Pentacam simulated K and 4.5‐mm EKR values; however, considerably large 95% LoA were found between each of these values and those obtained with the clinical history method. Estimated preoperative keratometry was statistically similar to the preoperative measurement; however, estimated refractive change was different from actual value. Conclusions: The Pentacam 4.5‐mm EKR and simulated keratometry may be used as an alternative to clinical history method to predict corneal power when pre‐keratorefractive surgery data are unavailable; however, wide LoA should be considered in the calculations.     

Repeatability and agreement of CCT measurement in myopia using entacam and ultrasound pachymetry

AIM: To evaluate the repeatability of central corneal thickness (CCT) measurement by entacam, and agreement of CCT measured by Pentacam and ultrasound pachymetry (USP) in Chinese myopia. Thereby investigate the possibility of Pentacam as a substitute for USP in CCT measurement before refractive surgery. The effects of corneal curvature measured by Pentacam on CCT were also evaluated. METHODS: One hundred and forty-eight right eyes of 148 individual with myopia were included in this study. Three successive Pentacam CCT measurements followed by 10 successive ultrasound pachymetry were carried out in the 148 eyes. Mean of CCT taken by each device was calculated for comparison. According to the CCT measured by USP, all the 148 eyes were divided into 3 groups: <520μm, 520-560μm, >560μm. For all eyes and each group the CCT obtained by Pentacam and USP were compared. Anterior corneal curvature of the 148 eyes was also adopted for correlation analysis with CCT obtained by ultrasound pachymetry. In addition, CCT measurement using 60 random selected Scheimpflug images was performed by 3 skilled investigators at different time, and this was repeated for 3 times by a forth investigator to assess repeatability of Pentacam CCT measurement using Scheimpflug images. RESULTS: Intraclass correlation coefficient (ICC) analysis revealed high intraobserver repeatability (ICC=0.994, F=158.60, P<0.001) for CCT measurement by Pentacam. The interobserver (ICC=0.998, F=494.73, P<0.001) and intraobserver (ICC=0.997, F=383.98, P<0.001) repeatability for Pentacam CCT measurements using Scheimpflug images were also excellent. There was high positive correlation between the CCT values measured by Pentacam and ultrasound pachymetry (r=0.963, P<0.001). Bland-altman plots showed that the Pentacam underestimate the CCT by 8.02μm compared with ultrasouond pachymetry. The differences between Pentacam and USP increased as the CCT readings by USP increased (Pentacam vs USP: slope=-0.04, P<0.05). The 95% upper and lower limits of agreement between CCT values obtained from the two devices were +9.33μm and -25.37μm. No significant association could be found between CCT and anterior corneal curvature. CONCLUSION: Inter- and intraobserver variability for CCT measurements by Pentacam was considerably below clinically significant levels. CCT of myopia obtained by Scheimpflug camera, Pentacam, were highly correlated to that by ultrasound pachymetry. However, the values obtained are not directly interchangeable between Pentacam and ultrasound pachymetry as the 95% limits of agreement are relatively wide. Pentacam can be a useful instrument for measuring CCT in candidates to refractive surgery in clinic.     

Pentacam、IOLmaster和A型超声测量仪测量前房深度的比较

目的：比较Pentacam、IOLMaster和A型超声测量仪测量前房深度(anterior chamber depth,ACD)的准确性。

方法：观察性对照研究。对69例(138眼)近视患者由同一操作者分别使用Pentacam、IOLMaster和A型超声测量仪进行ACD测量,并对所得数据进行统计学分析。3种仪器的测量值一致性比较采用Bland-Altman检验,且用组内标准差及计算重复性系数来评价3种方法的重复性。

结果：Pentacam,IOLMaster和A型超声测量仪测得ACD值分别为(3.77±0.24)、(3.73±0.23)、(3.69±0.22)mm。Bland-Altman分析显示,3种方法测量ACD的平均值一致性较好(Pentacam vs IOLMaster：CoA 0.04mm,LoA -0.05～0.13mm; A超 vs IOLMaster：CoA 0.04mm,LoA -0.17～0.08mm; Pentacam vs A超：CoA 0.08mm,LoA -0.06～0.22mm)。组内标准差及计算重复性系数显示3种方法测量ACD的重复性好(S_w=0.03、0.02、0.03; 2.77 S_w=0.08、0.06、0.08)。3种仪器测量ACD值相互正相关(r=0.946,0.987,0.951,P<0.001)。

结论：Pentacam、IOLMaster和A型超声3种方法测量ACD的可重复性均很好、变异小、高度相关。Pentacam测得的ACD值稍大于A型超声,但由于3组数据可重复性好,变异系数小,故此差异没有重要的临床意义。     

Interocular differences of the Pentacam measurements in normal subjects

Purpose: The aim of this study was to determine the interocular differences of the Pentacam corneal measurements in a normal population. Methods: A retrospective analysis was performed on 550 eyes of 275 consecutive subjects evaluated for refractive surgery at the Rassoul Akram Hospital, Iran University of Medical Sciences. A Pentacam Scheimpflug camera was used for corneal measurements. Statistical analysis was performed to determine the normal levels of the difference between the two eyes. Results: One hundred and four men and 171 women with a mean age of 29.1 ± 7.73 years were evaluated. The mean (range) interocular difference was 2.17 (zero to 21) µm for maximum anterior elevation (AEmax), 3.62 (zero to 31) µm for maximum posterior elevation (PEmax), 8.42 (zero to 30) µm for minimum corneal thickness (CTmin), 0.06 (zero to 0.4) mm³ for three millimetre corneal volume (CV3), 0.19 (zero to 1.2) mm³ for five millimetre corneal volume (CV5), 0.44 (zero to 2.9) mm³ for seven millimetre corneal volume (CV7), 0.24 (zero to 2.5) dioptres for the mean keratometry (Km) and 0.39 (zero to 2.5) D for measurements of the corneal dioptric power in the steepest meridian (Kmax). Conclusions: Individuals with differences greater than 17.4 µm in AEmax, 29.1 µm in PEmax, 29.6 µm in CTmin, 2 D in Km, 2.27 D in Kmax, 0.32 in CV3, 1.05 in CV5, and 2.6 in CV7 between eyes represent less than 0.5 per cent of the population. An interocular difference outside the normal range should alert the clinician to examine for other parameters that are more predictive of post‐refractive surgical ectasia.     

Stability of posterior corneal elevation one year after myopic laser in situ keratomileusis

Purpose: The aim was to describe the forward shift of the posterior corneal surface one year after myopic laser in situ keratomileusis (LASIK) relative to the estimated residual stromal bed thickness (RBT) and to correlate RBT with the ablation percentage per total corneal thickness (CT) in eyes without significant changes in anterior best‐fit sphere (BFS) and corneal thickness one year after LASIK. Methods: The anterior and posterior BFS and central and peripheral corneal thickness were measured in 86 eyes from 43 patients (mean age 32.07 ± 7.01 years), who underwent uneventful LASIK for myopia using Orbscan before and one, six and 12 months after LASIK. The patients were divided into three groups based on estimated RBT (Group 1 with 16 eyes [19%], RBT less than 250 µm, Group 2 with 52 eyes [58%], RBT from 250 to 300 µm and Group 3 with 20 eyes [23%], RBT greater than 300 µm) and into two groups based on ablation percentage (Group A, 52 eyes [60%], less than 20% and Group B, 34 eyes [40%], more than 20%). Results: The mean posterior forward shifting was 9.4 ± 14.3 µm (range ‐27 to 80 µm) (p < 0.05), 4.0 ± 9.8 µm (range ‐34 to 24 µm) (p > 0.05) and 3.1 ± 8.8 µm (range ‐37 to 21 µm) (p > 0.05) at one, six and 12 months following LASIK, respectively. The posterior corneal forward shift was higher and showed an increasing trend in Group 1 (r²= 0.111), Group 2 (r²= 0.185) and Group B (r²= 0.156). Non‐significant (p > 0.05) posterior elevation was found in Group 3. The anterior BFS and central and peripheral corneal thickness did not show statistically significant differences (p > 0.05) for all post‐LASIK follow‐up visits. Conclusions: The posterior corneal displacement measured with Orbscan after LASIK was time dependent, with a different trend between estimated residual stromal bed thickness that protruded at an early stage but then returned to original levels 12 months after LASIK in eyes without post‐LASIK anterior topographic or pachymetric changes.     

Central corneal thickness measurements in unoperated eyes and eyes after PRK for myopia using Pentacam, Orbscan II, and ultrasonic pachymetry

PURPOSE: To compare central corneal thickness measurements obtained in unoperated eyes and eyes after myopic photorefractive keratectomy (PRK) using a rotating Scheimpflug camera (Pentacam), a scanning slit corneal topography system (Orbscan II), and ultrasonic pachymetry. METHODS: Corneal thickness was measured using Pentacam, Orbscan II, and ultrasonic pachymetry in 25 unoperated eyes (unoperated group), 24 eyes 1 to 3 months after myopic PRK (early postoperative PRK group), and 21 eyes 4 months or more after myopic PRK (late postoperative PRK group). RESULTS: In the unoperated group, corneal thickness measurements were similar for all three methods (P=.125). In the early postoperative PRK group, Orbscan measurements were thinner than Pentacam and ultrasonic measurements by a mean of 69.4 microm and 63.4 microm (P<.001 and P=.002, respectively). In the late postoperative PRK group, Orbscan measurements were thinner than Pentacam measurements by a mean of 36.0 microm (P=.017). Pentacam and ultrasonic pachymetry measurements were similar for all three groups with a mean difference of approximately 10 microm. CONCLUSIONS: Following myopic PRK, Pentacam was comparable to ultrasonic pachymetry in measuring corneal thickness, whereas Orbscan measurements were thinner.     

Agreement and repeatability of central corneal thickness measurements made by ultrasound pachymetry and anterior segment optical coherence tomography

PurposeTo evaluate repeatability within and between examiners and to assess agreement in corneal thickness measurements obtained by anterior segment optical coherence tomography (ASOCT) and ultrasonic pachymetry (USP).MethodsThis was a prospective, observational study. Fifty-one patients who visited a glaucoma service with suspected glaucoma, glaucoma, or cataract were enrolled. Patients with a history of corneal surgery or abnormalities and those who were uncooperative for examinations were excluded. Each patient underwent ASOCT followed by USP, with each test performed by two different examiners. Measurement repeatability was evaluated using intraclass correlation coefficient (ICC) values. Agreement in corneal thickness measurements was evaluated by the Bland and Altman plot method. Linear regression analysis was used to assess the relationship between ASOCT and USP measurements.ResultsUSP and ASOCT corneal thickness measurements revealed high intraexaminer and interexaminer repeatability (ICCs ≥ 0.978). ASOCT corneal thickness measurements of a central 2-mm zone showed higher intraexaminer (ICC = 0.999) and interexaminer (ICC = 0.999) repeatability than USP measurements or ASOCT measurements of the vertex. The 95% limit of agreement (LoA) between the vertex-centered ASOCT and the USP scan was between 3.68 and 24.76 μm. The 95% LoA between the central 2-mm zone ASOCT and the USP scan was between 3.75 and 23.39 μm. Average ASOCT corneal thickness was less than USP measurements, but ASOCT thickness could be converted to USP thickness through linear regression equations.ConclusionBoth devices have good intraexaminer and interexaminer repeatability, though ASOCT has slightly better interexaminer repeatability. ASOCT accurately and reliably measures corneal thickness in a noninvasive manner.     

The relationship between central corneal thickness and Goldmann applanation tonometry

Background: The aim of this study was to investigate the relationship between Goldmann applanation tonometry and central corneal thickness in a large sample of healthy eyes. Method: Five hundred eyes of 500 subjects (253 women, 50.6 per cent and 247 men, 49.4 per cent) were analysed in a prospective healthy population study. Mean age of the sample was 31 ± 8 years. Goldmann applanation tonometry was carried out by one physician. Tonometric values were the mean of three consecutive readings. Subsequently, another physician carried out ultrasonic pachymetry with the DGH 2000 AP ultrasonic pachymeter (DGH Technology Inc, San Diego, USA). Ten measurements were made at the centre of the cornea of each eye. The lowest value was used for analysis. Results: Applanation tonometry and central corneal thickness were correlated (r = 0.184, p < 0.001). There was no significam correlation between corneal thickness and age (r = 0.083, p = 0.065), mean spherical equivalem refraction (r = 0.083, p = 0.065) or visual acuity (r = 0.036, p = 0.187). Conclusion: In normal eyes, there is no statistically significant correlation between changes of intraocular pressure and changes of central corneal thickness but they suggest a relationship between intraocular pressure and central corneal thickness. Goldmann applanation tonometry has a systematic error in accuracy of intraocular pressure readings of healthy eyes caused by its dependence on central corneal thickness. Measurement of corneal thickness by optometrists should be the first step in diagnosing intraocular pressure pathologies.     

Pentacam系统与A超角膜测厚仪测量瞳孔中心角膜厚度的比较

目的比较Pentacam三维眼前节分析诊断系统与A型超声角膜测厚仪在正常人与近视眼患者瞳孔中心角膜厚度的测量结果,为临床使用提供依据。方法首先对正常人50只眼连续进行3次Pentacam系统检查,以评价该系统对角膜厚度测量的重复性。进而选取217例(433只眼)拟行准分子激光原位角膜磨镶术(LASIK)的屈光不正患者和LASIK术后6个月以上患者63例(126只眼),分别应用Pentacam系统和A超进行角膜厚度测量,并对检查结果进行统计学分析。结果50只正常眼瞳孔中心角膜厚度重复测量结果差异无统计学意义(P>0.05),表明Pentacam系统检查结果重复性很好。在对角膜厚度的测量结果中,术前A超测厚和Pentacam系统测量的瞳孔中央角膜厚度分别为(537.26±31.61)和(538.08±32.72)μm,术后分别为(464.21±41.04)和(465.17±42.65)μm,术前后两种测量方法的结果之间差异均无统计学意义(P>0.05),两种测量结果之间具有密切的线性相关(P<0.001),其中术前两种仪器测量结果的差值在20μm以内的达95.38%。角膜最薄点多位于距角膜顶点周围1mm范围内稍偏颞下方。结论用Pentacam三维眼前节分析诊断系统进行LASIK术前后角膜厚度的测量,结果准确、全面、方便,具有较好的临床应用价值。(中华眼科杂志,2006,42985-988)     

Measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients

AIM: To evaluate the measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients.METHODS:A hundred and one eyes of 55 keratoconus patients were enrolled in this study. The mean age was 26.2±8.9 years. The inclusion criteria were keratoconus stage I to III according to the Amsler-Krumeich keratoconus classification. All the measurements were done by the same operator, under the mesopic light condition and repeated with three different optical methods; Visante , Orbscan and Pentacam. The evaluated anterior segment parameters were anterior chamber depth (ACD), central and thinnest corneal thickness (CCT and TCT) and pupil diameter (PD).RESULTS: The mean CCT measured by Visante, Orbscan and Pentacam were as follows:462.0±48.1μm, 463.9±60.9μm, 476.5±45.3μm, respectively (P=0.873). The mean ACD values were 3.34±0.33mm, 3.26±0.33mm, 3.49±0.40mm, respectively (P=0.118). The mean PD measurements were 5.11±1.14mm, 4.80±0.85mm, 3.80±1.38mm, respectively (P<0.001). The mean TCT measurements of Visante, Orbscan and Pentacam were 437.9±48.2μm, 447.6±60.6μm and 459.9±44.0μm, respectively (P=0.214). The Visante and Orbscan measured CCT similarly, while Pentacam measured CCT thicker than the other two. The Visante measured TCT thinner than the other two devices. In ACD measurements, Orbscan was the one giving the lowest values. PD was measured differently by the devices.CONCLUSION: Although TCT, CCT and ACD measurements acquired by Visante, Orbscan and Pentacam in keratoconus patients are similar, PD measurements show large differences among the devices.