Measuring corneal thickness with a rotary scanning system

PURPOSE: Recently the authors presented a technique that allows measurement of the corneal thickness along a vertical meridian from optical sections obtained using a slit-lamp microscope. We present a new system that allows rotary scanning of the cornea and consequent measurement of the corneal thickness along any meridian. METHOD: The corneal thickness along two perpendicular meridians was measured from optical sections obtained with a new rotary scanning system. To obtain the optical sections, the cornea is illuminated with a light beam that is previously expanded in a fan by a small cylindrical lens rotated on a plane-containing axis to explore the cornea. The light diffused by both corneal surfaces is collected by two video cameras placed at an angle with the light beam. The axes of the two cameras define, with the visual axis, two planes normal to each other. After image acquisition, a processing algorithm is applied in order to compute the corneal thickness along the two meridians. RESULTS: Some preliminary results for the vertical and the horizontal meridians of one eye are shown, as well as all the intermediate computations. CONCLUSIONS: With this system, we expect to be able to measure corneal topography and thickness along an arbitrary meridian. The rotary scanning of the cornea is mechanically simple and will eventually allow automated scanning.     

Comparison of central corneal thickness measurements between optical and ultrasound pachometers.

The central corneal thickness measured by 2 methods was compared in 31 normal subjects. At each of the two examinations, central corneal thickness was evaluated by an ultrasonic and an optical method. Reliability was assessed by an analysis of variance (ANOVA) between repeated measurements for the electronic digital and the Humphrey ultrasonic pachometers. The former revealed a systematic right-left difference, the left cornea being significantly thicker. This phenomenon has been observed in many studies and has been attributed to a measurement not done perpendicularly to the cornea. Angle lambda measured on eight subjects was nasal in all cases. A very high correlation coefficient was obtained between the two methods of central pachometry and the results obtained for the right eye by these two methods were not significantly different. Also, a small but significant negative correlation was observed between the central corneal curvature and the corneal thickness as evaluated by either pachometer.     

正常人中央角膜厚度与Goldmann压平眼压的关系

目的:了解正常人中央角膜厚度(central corneal thickness,CCT)的分布特点并探讨其与压平眼压测量值的关系。方法:采用光学角膜测厚仪及Goldmann压平眼压计检测169名正常人CCT和压平眼压。结果:169名受检者右眼平均CCT为0.547mm(95%可信区间0.443~0.651mm),左眼0.551mm(95%可信区间0.453~0·649)。压平眼压右眼平均15.8mmHg,左眼15.5mmHg。CCT与年龄无相关关系,但与压平眼压测量值显著相关。线性回归分析表明,CCT每增加0.018mm,压平眼压增加1mmHg。结论:CCT变异是眼压测量误差的主要来源。CCT较厚的正常个体可表现"眼压增高"被误诊为高眼压症,而CCT偏薄的原发性开角型青光眼患者则可能因眼压测量"正常"被误诊为正常眼压性青光眼。在诊断青光眼或高眼压症时,特别是在眼压值与其他临床表现不符时,应考虑CCT有无变异。     

Silicone-acrylate contact lenses for myopia control: 3-year results

One hundred myopic children between the ages of 8 and 13 years were fitted with Paraperm O2plus silicone-acrylate contact lenses. After 3 years of lens wear, the mean increase in myopia for the 56 subjects remaining in the study was 0.48 D (+/- 0.70) D as compared with 1.53 (+/- 0.81) D for a group of spectacle-wearing myopes matched for initial age and initial refractive error. The mean change in corneal refracting power for the contact lens wearers was a decrease (corneal flattening) of 0.37 (+/- 0.32) D. Assuming that little or no corneal change would have occurred in the absence of the contact lenses, we may conclude that corneal flattening (as measured by the keratometer) accounts for less than half of the effect of contact lenses in controlling myopia progression. A possible explanation for this disparity is that although the keratometer provides a valid measurement of corneal refracting power for a "normal" cornea, it fails to provide a valid measurement for a cornea that has been flattened by wearing a contact lens.     

Interlamellar adhesive strength in human eyebank corneas

The interlamellar biomechanical properties of stromal collagen are relatively unknown, yet may be highly significant with respect to wound healing and the efficacy of certain keratorefractive surgical procedures. Interlamellar adhesive strength was measured as the tearing force required to separate corneal lamellae at a 50% stromal depth in 16 human eyebank corneas. The mean value for the central cornea was found to be 14.2 (+/- 0.5 SEM) g-wt/mm of tissue width. Histology showed a smooth separation between the lamellae along the tearing plane in the central cornea. We believe that the adhesive strength measured in the central cornea may be primarily the force needed to break interlamellar proteoglycan bonds between collagen lamellae, because no torn lamellae were found in this region. The mean adhesive strength and the SEM increased toward the periphery in a symmetrical fashion. The mean adhesive strength in the far periphery was 31.6 (+/- 3.7 SEM) g-wt/mm at 5 mm nasally, and 28.4 (+/- 3.2 SEM) g-wt/mm at 5 mm temporally, and was approximately twice the mean central value. The rising value of the mean adhesive strength with increasing distance from the central cornea was believed to be due to a more highly disorganized collagen network in which greater numbers of lamellae passed obliquely in depth through the tearing plane. These lamellae would contribute their tensile strength to the adhesive strength measurement along the tearing plane. Histology from the peripheral cornea confirmed the existence of depth-varying collagen lamellae and the torn ends of lamellae that passed across the tearing plane.     

Corneal thickness in eyes with diabetic and nondiabetic neovascularisation.

The corneal thickness was measured in 20 patients with ocular neovascularisation of diabetic and nondiabetic aetiology. Mean corneal thickness (+/- SD) was 0.561 mm (+/- 0.027) and 0.499 mm (+/- 0.029) in the diabetic (n = 11) and the nondiabetic groups (n = 9), respectively (2p less than 0.001). The increased corneal thickness in the diabetic group is comparable to that previously reported in diabetics with proliferative retinopathy. These results indicate that the increased corneal thickness found in diabetics is peculiar to the diabetic eye and not secondary to the process of ocular neovascularisation as such.     

Corneal and epithelial thickness in keratoconus: a comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography

PURPOSE: To compare corneal thickness measurements in individuals with keratoconus using optical coherence tomography (OCT), Orbscan II, and ultrasonic pachymetry and to measure epithelial and stromal thickness in these individuals using OCT. METHODS: Twenty individuals with keratoconus and 20 controls (without keratoconus) were enrolled. The Orbscan II was used to locate the steepest area of the cornea, which was taken to represent the cone apex. Each instrument was used to obtain four total corneal thickness measurements-from the cone apex, corneal center, mid-nasal, and mid-temporal cornea. Optical coherence tomography scans were analyzed to provide epithelial and stromal thickness readings. RESULTS: In individuals with keratoconus, mean central corneal thickness (CCT) measured by ultrasonic pachymetry, Orbscan, and OCT was 494.2 +/- 50.0 microm, 438.6 +/- 47.7 microm, and 433.5 +/- 39.7 microm, respectively. The central keratoconic cornea was 57.7 microm thinner than the normal cornea (post-hoc P<.001). The cone apex was thinner than the central cornea (P<.001). Keratoconic epithelium was 48.2 +/- 5.5 microm centrally and 42.1 +/- 4.5 microm at the apex. Central keratoconic epithelium was 4.7 microm thinner and central keratoconic stroma was 57.8 microm thinner than the normal cornea (P<.001, respectively). Comparing instruments, Orbscan and OCT correlated in CCT measurement (r=0.890) and apical thickness (r=0.846). All instruments produced similar readings for mid-nasal and mid-temporal corneal thickness in participants with keratoconus (P>.05). CONCLUSIONS: Ultrasonic pachymetry produced the highest corneal thickness readings in the center and apex, compared to Orbscan II and OCT. Centrally, the total cornea, epithelium, and stroma were thinner in individuals with keratoconus than in normal individuals.     

近视眼角膜上皮厚度分布特点及其与角膜生物力学性能的关系

目的分析近视眼角膜不同区域的上皮厚度分布特点及其与角膜生物力学等因素的关系。方法 横断面研究。选取拟行准分子激光角膜屈光手术的近视及近视散光患者198例（198眼）,年龄18～41岁,等效球镜度-0.75～-10.38 D,将右眼数据纳入分析。应用RTVue眼前节OCT测量角膜中央0～2 mm直径区域平均上皮厚度,周边>2～5 mm及>5～6 mm 2个区域角膜上方、颞上方、颞侧、颞下方、下方、鼻下方、鼻侧、鼻上方等象限的上皮厚度。将角膜中央上皮按照厚度不同分为3组,应用眼反应分析仪（ORA）测量角膜滞后量（CH）、角膜阻力因子（CRF）,分析其与上皮厚度的关系。应用Mann-Whitney U检验、Kruskal-Wallis检验、多元线性回归分析、Spearman相关分析等方法对所测结果进行分析。结果角膜0～2 mm,>2～5 mm,>5～6 mm区域上皮厚度分别为54.0（52.0～56.0）μm,54.1（52.6～56.4）μm,53.8（52.2～55.8）μm,区域之间差异无统计学意义（Z=3.860,P＞0.05）。角膜8个象限之间的上皮厚度差异有统计学意义（Z>2-5 mm=279.482,P＜0.01;Z>5-6 mm=210.442,P＜0.01）,其中,上方（颞上方、上方、鼻上方）的上皮厚度明显比下方（颞下方、下方、鼻下方）薄（Z>2-5 mm=-5.243,P＜0.01,Z>5-6 mm=-8.101,P＜0.01）,鼻侧与颞侧差异无统计学意义（Z>2-5 mm=-0.481,P＞0.05,Z>5-6 mm=-0.381,P＞0.05）。随着角膜上皮厚度的增加,角膜的生物力学性能会相应地增强;不同角膜中央上皮厚度组间CH与CRF差异均有统计学意义（CH：Z=8.945,P＜0.05;CRF：Z=9.225,P＜0.05）。角膜中央上皮厚度与年龄呈负相关,即年龄越大,角膜上皮厚度越薄（r=-0.185,P＜0.01）;与屈光度不相关（r=-0.092,P＞0.05）。结论近视眼角膜上皮呈非均匀分布,除上方较下方偏薄外,各象限也存在厚度差异;角膜上皮对角膜生物力学性能有一定影响,角膜上皮越厚,相应的生物力学性能越强。     

Corneal thickness is reduced in dry eye.

PURPOSE: To evaluate and compare corneal thickness in normal and dry eyes. METHODS: The Orbscan corneal topography system was used to measure the corneal thickness at nine locations in the central and peripheral (superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal, superotemporal) cornea in 38 eyes of 21 patients with aqueous tear deficiency dry eye and 34 eyes of 21 normal subjects. RESULTS: The average thickness of nine sites in the central and midperipheral cornea was significantly decreased in dry eyes compared with that of normal eyes. The superior cornea was found to be the thickest area in both groups, measuring 0.629 +/- 0.030 mm in normal eyes and 0.589 +/- 0.031 mm in dry eyes. The center of the cornea was noted to be the thinnest in both groups, measuring 0.571 +/- 0.028 mm and 0.534 +/- 0.034 mm in normal and dry eyes, respectively. In color-coded pachymetry maps, the oval pattern was observed in 67.6% of normal corneas and 39.5% of dry eyes, while the decentered oval pattern was noted in 2.9% and 31.6% of normal and dry eyes, respectively (p < 0.025 for oval pattern and p < 0.005 for decentered oval map). The mean astigmatism was 0.99 +/- 0.43 diopter (D) in normal corneas and 1.42 +/- 0.92 D in dry eyes (p = 0.015). In the anterior elevation maps, the island pattern was the most commonly observed pattern in both groups, 88.3% in normal corneas and 60.5% in dry eyes (p < 0.01). No significant difference in the patterns of posterior corneal elevation maps and axial power maps of the anterior corneal surface was noted between groups. CONCLUSION: The corneal thickness of the central and midperipheral cornea was significantly decreased in the dry eyes. It is possible that the chronic state of desiccation and immune activation in dry eye may contribute to the observed corneal thinning. Perhaps the frank corneal ulceration that occurs in some dry eyes is a more severe manifestation of this phenomenon.     

近视眼角膜厚度及相关因素分析

目的:探讨青年近视患者角膜厚度分布特点及其相关因素。方法:选取青年近视患者200例(400眼),按屈光度不同分为4组,应用OrbscanⅡ眼前节分析系统对患者的角膜中央点、最薄点、后表面平均屈光度最大点,以及距中心1.5,2.5mm上方、下方、颞上、颞下、鼻上、鼻下、颞侧、鼻侧部位的角膜厚度及相应的前房深度、后表面高度、后表面曲率、前表面曲率进行测量。结果:角膜厚度呈中心薄周边厚分布,最薄点位于距中心2.5mm范围内(86%),角膜颞下部位(50%)。后表面平均屈光度最大点、最薄点、中央点三个点的角膜厚度在不同近视组中差异无统计学意义(P>0.05)。不同部位的角膜厚度与其他因素相关分析。结果:中央点:角膜厚度与前房深度、前表面曲率负相关(r=-0.181,-0.103,P=0.000,0.039)。最薄点:角膜厚度与相应的前房深度、后表面高度、后表面曲率绝对值、前表面曲率呈负相关(r=-0.167,-0.113,-0.104,-0.109;P=0.001,0.024,0.038,0.03)。后表面屈光度最大点:角膜厚度与相应的前房深度、后表面高度、后表面曲率绝对值、前表面曲率呈负相关(r=-0.342,-0.138,-0.189,-0.159;P=0.000,0.000,0.000,0.001)。结论:角膜厚度最薄点多位于旁中心2.5mm颞下部位;角膜厚度与近视程度无关;角膜厚度与相应的前房深度、后表面高度、后表面曲率绝对值、前表面曲率为负相关关系。     

Corneal thickness measurement by confocal microscopy, ultrasound, and scanning slit methods

PURPOSE: To measure corneal thickness by using a calibrated confocal microscope and to compare this measurement to thickness determined by ultrasonic and noncontact scanning slit pachymetry. DESIGN: Comparison of corneal thickness measured by using four instruments in normal subjects. METHODS: Thickness measured by a clinical confocal microscope (Tandem Scanning) was calibrated from measurements of polymethylmethacrylate contact lenses with known thickness. Corneal thickness was measured in one eye of 24 normal subjects by using this instrument, two ultrasonic pachymeters (DHG-1000 and Sonogage), and a noncontact optical scanning slit pachymeter (Orbscan II). RESULTS: Mean corneal thickness measured by confocal microscopy was 516 +/- 30 microm (+/-SD). This was less than the mean thickness measured by both ultrasonic pachymeters, 554 +/- 28 microm by the DGH, and 555 +/- 28 microm by the Sonogage (P <.001). Thickness measured by the Orbscan II pachymeter was 540 +/- 35 microm (P <.001, compared with either confocal or ultrasound) after applying an "acoustic factor" of 0.92, a default correction of the software. CONCLUSION: Corneal thickness measured by calibrated confocal microscopy is approximately 39 microm (7.0%) less than thickness measured by two commonly used ultrasonic pachymeters and approximately 24 microm (4.4%) less than thickness measured by the corrected Orbscan II pachymeter. These differences are important for planning and measuring the effects of refractive and other surgical procedures. The precision of confocal microscopy is limited by corneal motion in an anterior-posterior direction. The difference between instruments suggests that verification of clinical ultrasonic pachymeters should be revisited.     

Diurnal and long-term variations in corneal thickness in the normal and alloxan-induced diabetic rabbit

The variation of central corneal thickness with age was measured weekly at 10am by ultrasound pachometry in 10 normal (5 to 19 weeks of age) and 10 alloxan-induced diabetic (9 to 19 weeks of age) rabbits. The diurnal variation of corneal thickness was also measured at 2 hour intervals for a period of 24 hours on both groups of rabbits at 19 weeks of age. A nonlinear increase in corneal thickness with age was noted in both groups, with the diabetic cornea becoming significantly thicker (p less than 0.05) than the normal control after 7 weeks of hyperglycemia. At 19 weeks of age, the diabetic rabbit cornea (379 +/- 18um) was 5.2% thicker than the normal control (360 +/- 10um). Both normal (26um) and diabetic (26um) rabbits demonstrated a similar sinusoidal diurnal variation of corneal thickness, with the cornea being thinnest in both groups near midnight. A negative exponential function derived using nonlinear regression analysis was found to adequately describe the age data, and could be used to provide a number of possibly useful clinical indices of corneal thickness variation with age. The data from this study demonstrate that 1) the variation of rabbit corneal thickness with age can be modelled using a negative exponential function, 2) alloxan-induced hyperglycemia is associated with an increase in rabbit corneal thickness, 3) alloxan-induced hyperglycemia does not appear to influence the diurnal variation of rabbit corneal thickness and 4) care should be taken in the interpretation of in vivo corneal thickness studies using normal rabbits of under 12 weeks of age (2kg body weight).     

Optische Online-Pachymetrie bei Laser-in-situ-Keratomileusis

PURPOSE: Currently the microkeratome incision and the ablation depth are unpredictable in laser in situ keratomileusis (LASIK). Online optical coherence pachymetry is a high-resolution and non-contact method, which enables the corneal thickness changes to be monitored intraoperatively. METHOD. In 12 patients undergoing myopic LASIK, online optical coherence pachymetry with a wavelength of 1310 nm and a measurement frequency of 74 Hz was studied. The central corneal thickness changes were determined continuously. RESULTS: Online optical coherence pachymetry enabled intraoperative visualization and assessment of the central corneal thickness, the flap thickness after the microkeratome pass, the time-resolved ablation and the residual stromal thickness. Intraoperatively the mean flap thickness was 113+/-31 microm and the residual stromal thickness was 277+/-49 microm. The optically determined ablation depth was 116+/-30 micro m, which corresponded to 33 microm higher mean values than the nominal ablation depth. CONCLUSIONS: Online optical coherence pachymetry enabled the flap and residual stromal thickness to be measured intraoperatively. Also the individual ablation depth and possible dehydration effects of the cornea were monitored continuously. Thus, online optical coherence pachymetry could contribute to improve the safety standards during LASIK.     

圆锥角膜的光密度分析

目的 使用Pentacam对圆锥角膜和健康角膜的光密度进行测量,比较健康角膜与不同等级圆锥角膜的透明度.方法 使用Pentacam眼前节分析系统测量对照组(30例30眼正常角膜)以及圆锥角膜组(36例36眼圆锥角膜)的光密度,以角膜顶点为中心,分别测量0～2 mm、2～6 mm、6～ 10 mm、10 ～ 12 mm直径范围的前层(120μm)、后层(60 μm)以及中间层的角膜光密度.使用Amsler-Krumeich分级方法对圆锥角膜进行分级,对比不同等级光密度差异.分析圆锥角膜光密度与厚度、陡峭K值的相关性.结果 总直径的全层角膜光密度圆锥角膜组(17.96±3.23)和对照组(17.39±1.95)之间差异无统计学意义(P =0.124);但是在0～2 mm直径范围内的前层、中层、全层,2～6mm直径范围内的前层以及总直径的前层中,圆锥角膜组的光密度均显著高于对照组(均为P＜0.05).按照圆锥角膜等级分组,对照组角膜光密度与轻度圆锥角膜组各层比较,差异均无统计学意义(均为P＞0.05),但对照组角膜光密度与中度圆锥角膜组0～2mm直径范围内的前层比较差异有统计学意义(P＜0.05).重度圆锥角膜在0～2 mm直径范围内各层光密度较对照组、轻度圆锥角膜组、中度圆锥角膜组均显著增高(均为P＜0.05),在2～6 mim直径范围和总直径的前层、中层和全层与其余三组相比均显著增加(均为P＜0.05).圆锥角膜组的陡峭K值与0～2 mm直径范围的总角膜光密度显著相关(P＜0.05).圆锥角膜组的角膜顶点以及角膜最薄点的厚度与光密度也存在明显的相关性(均为P＜0.05).结论 相比正常角膜,轻度圆锥角膜光密度不发生改变,中度圆锥角膜光密度增高主要发生于角膜前层0～2 mm直径范围内,重度圆锥角膜光密度增高主要发生于角膜前层0～6 mm直径范围内和角膜中层2 mm直径范围内,而且圆锥角膜光密度随疾病发展而增高.角膜光密度是圆锥角膜的一个重要参考指标,可以用来检测圆锥角膜发病进程以及治疗效果.     

角膜厚度测量的研究进展

中央角膜厚度对角膜疾病、青光眼、角膜屈光手术等眼部疾病和手术有重要影响，获得精准的角膜中央厚度为临床医师提出了更高的要求，也是大家一直非常关注的话题。目前，临床中常用的角膜厚度测量仪器有2类原理：第一类为超声波测量，例如传统的A型超声角膜测厚仪(A超)、超声生物显微镜(UBM)； 第二类是光学测量原理，包括Pentacam眼前节分析仪、角膜内皮镜、光学相干断层扫描仪(OCT)、Lenstar LS900光学生物测量仪。不同的测量方法和相应仪器都具有各自的优点及不足。角膜厚度测量最佳的发展方向应为简单易用、重复性好、准确性高。因此对目前临床常用的角膜厚度测量仪器的原理及特点进行综述，总结当下角膜测厚的研究进展，为临床眼科医生提供理论依据和临床指导。     

Noncontact corneal pachymetry with slit lamp-adapted optical coherence tomography

PURPOSE: The purpose of this study was to determine the accuracy, the reproducibility, and the limits of agreement of noncontact central corneal thickness measurement with slit lamp-adapted optical coherence tomography (OCT). DESIGN: Nonrandomized comparative clinical trial. METHODS: In a prospective comparative observational study, a total of 108 consecutive patients (108 eyes) with normal corneas (92 eyes) and different corneal alterations (16 eyes) participated. Six sequential measurements of the central corneal thickness with slit lamp-adapted OCT and with ultrasound (US) pachymetry at 1640 ms(-1) were performed. The main outcome measures were accuracy, reproducibility assessed with precision and coefficient of variation (CV), and limits of agreement of central corneal thickness measurement. RESULTS: The mean central corneal thickness values were 541 +/- 43 microm (OCT) and 549 +/- 44 microm (US) with a mean precision of +/- 5.8 microm (CV 1.08%) and of +/- 4.0 microm (CV 0.73%), respectively. The method comparison revealed equivalence (+/- 2SD) in the 5% range with a mean difference between both methods of 7.9 microm (1.45%). The relative error was 8.7 microm (1.6%), which corresponded to limits of agreement (+/- 2SD) ranging from -9.5 microm to 25.3 microm. CONCLUSIONS: Central corneal pachymetry with slit lamp-adapted OCT revealed, for clinical purposes, an excellent accuracy and reproducibility with a high degree of agreement compared with US pachymetry. Thus, the presented OCT system seems to be a promising diagnostic modality to objectively measure corneal thickness in a convenient noncontact mode.     

Comparison of optical and ultrasound pachometry

PURPOSE: (1) To determine the agreement between optical and ultrasound pachometry for central corneal thickness measurements used to "correct" applanation intraocular pressure (IOP) readings. (2) To determine the inter- and intra-observer variability of optical and ultrasound pachometry. METHOD: Central corneal thickness (CCT) was measured in a masked manner using optical and ultrasound pachometry in 50 normal eyes. To assess intra- and inter-observer variability, multiple masked measurements were obtained in 51 eyes (optical pachometry) and 34 eyes (ultrasound pachometry). Agreement was determined by a published technique that uses the mean of the differences, standard error (SE) and standard deviation (SD). RESULTS: The mean difference in CCT between optical and ultrasound pachometry was 0.001 mm (SD 0.031 mm; SE 0.00439 mm). The mean inter-observer difference for the optical pachometer was 0.019 mm (SD 0.049 mm; SE 0.0069); the mean intra-observer difference was 0.003 mm (SD 0.017; SE 0.0.0024). The mean inter-observer difference for ultrasound pachometry was 0.001 mm (SD 0.009; SE 0.0015) and the mean intra-observer difference was 0.002 mm (SD 0.011; SE 0.0019). CONCLUSIONS: Ultrasound pachometry is the more reliable method for the measurement of central corneal thickness used to correct applanation IOP values. Optical pachometry had good intra-observer variability. The range of error in IOP correction for corneal thickness (inter-observer) that can occur using the ultrasound pachometer is -1.2 mmHg to +1.4 mmHg as compared to -5.6 mmHg to +8.5 mmHg with the optical pachometer.     

Distribution of corneal spherical aberration in a comprehensive ophthalmology practice and whether keratometry can predict aberration values

PURPOSE: To determine the spherical aberration of the cornea in the general population and whether keratometry readings are predictive of corneal spherical aberration values. SETTING: Private comprehensive ophthalmology practice. METHODS: Corneal spherical aberration and keratometry readings were measured in 696 normal eyes of patients presenting for ocular examination to a comprehensive ophthalmologist. The Easygraph (Oculus) was used to measure the corneal topography and keratometry readings in patients with healthy corneas. The analysis was performed using software in the Easygraph to determine the Zernike coefficients for each cornea. The keratometry and spherical aberration (Zernike coefficient Z(4)(0)) were then statistically analyzed. RESULTS: The corneal spherical aberration, analyzed by the Kolmogorov-Smirnov test for normality, fit a normal Gaussian distribution. The spherical aberration value was (+0.274 +/- 0.089) x 10(-3), measured at an optical zone of 6.0 mm. A very weak correlation was found between corneal spherical aberration and central keratometry readings of the cornea: Corneal spherical aberration = {0.017 x (mean keratometry) - 0.457} x 10(-3). CONCLUSIONS: The corneal spherical aberration distribution was a normal Gaussian curve. However, the mean value was significantly different when the sex of the patient was considered. Corneal keratometry readings could not be reliably used to predict corneal spherical aberration.     

糖尿病视网膜病变不同分期角膜及角膜上皮厚度变化

目的：对比分析糖尿病视网膜病变（DR）不同分期患眼和正常眼的角膜及角膜上皮厚度的变化情况。 方法：系列病例研究。选择2018年1月1日至2020年1月31日于山西省眼科医院就诊并确诊为DR的患者100例（103眼）,其中非增殖期组（NPDR）50例（53眼）,增殖期组（PDR）50例（50眼）。另随机 选取正常志愿者46例（48眼）,利用频域前节光学相干断层扫描技术（AS-OCT）对非增殖期组、增殖期组及正常组均进行中心2、5、7、9 mm共4个同心圆区域扫描范围的角膜及角膜上皮厚度检查分析。 采用单因素方差分析比较3组DR患者的角膜及角膜上皮各区域平均厚度。结果：3组间中央前、后角膜曲率及中央角膜厚度差异均无统计学意义（F=1.84,P=0.16;F=1.88,P=0.16;F=1.96,P=0.15）, 正常组中央角膜上皮厚度均高于其余2组（P<0.05）。正常组与NPDR组角膜上皮厚度多区域差异均有统计学意义（P<0.05）;正常组与PDR组角膜上皮厚度多区域差异均有统计学意义（P<0.05）;NPDR组与PDR组角膜上皮厚度只有S5 mm、SN5 mm、ST5 mm、T7 mm共4个区域差异有统计学意义 （P<0.05）,其余区域差异无统计学意义。结论：DR发展的不同阶段会对角膜上皮组织厚度产生潜在影响,这种变化可能可以作为DR筛查的指标之一。     

Corneal thickness and endothelial cell density measured by non-contact specular microscopy and pachymetry in Rhesus macaques (Macaca mulatta) with laser-induced ocular hypertension

PURPOSE: Sustained increase in intraocular pressure (IOP) in humans results in a loss of corneal endothelial cells and an increase of corneal thickness. The effects of chronically elevated IOP on the corneal endothelium of monkeys with laser-induced ocular hypertension, a commonly used animal model of human glaucoma have not been documented. This study examined the central corneal thickness (CCT), the corneal endothelial cell density (ECD), and the corneal endothelial cell size (ACS) in Rhesus monkeys with experimental ocular hypertension.Materials and methods. Ten male monkeys with argon laser-induced ocular hypertension in one eye for an average duration of 2.4+/-0.7 years, were sedated with ketamine hydrochloride, and the CCT, ECD, and ACS measured at the center of the cornea of both eyes with a Topcon SP-2000P non-contact specular microscope (Topcon America Corporation((R)), Paramus, NJ, USA). CCT was also measured using a DHG-500 Pachette ultrasonic pachymeter (DHG Technology Inc., Exton, PA, USA). Mean and standard deviation (S.D.) of CCT, ECD and ACS for each eye was calculated and statistically compared.Results. Mean CCT in the hypertensive and normal eyes measured by specular microscopy was 0.477+/-0.023mm and 0.468+/-0.020 mm, respectively. Mean ECD in the hypertensive and normal eyes was 2601.7+/-631.8 and 3990.2+/-402.9 cells mm(-2), respectively. The mean size of the endothelial cells was 252.4+/-23.9 micro m(2) in the normal eye and 408.7+/-115.0 microm m(2) in the hypertensive eye. No significant difference in the measurement of CCT was observed between the specular microscope and the pachymeter (p=0.46).No significant difference in the mean CCT was observed between the two eyes (p=0.4820), whereas the mean ECD was significantly lower in the hypertensive eye than in the normal eye (p<0.001). The ECD was inversely related to the length of IOP elevation (p<0.001). CONCLUSIONS: No difference in the corneal thickness measurement was observed between the specular microscopy and the pachymetry techniques. Chronic ocular hypertension did not significantly affect the CCT, but caused a significant loss of endothelial cells in the center of the cornea of the laser treated eyes compared to the normotensive eyes. The duration of elevated IOP was the most important factor affecting the ECD.