Central corneal thickness and thickness of the lamina cribrosa in human eyes

PURPOSE: Since central corneal thickness may inversely influence the amount and rate of progression of glaucomatous optic nerve damage and because lamina cribrosa thickness may be of importance in susceptibility to glaucoma, it was the purpose of the present study to evaluate whether central corneal thickness is related to lamina cribrosa thickness. METHODS: The histomorphometric study included 111 enucleated nonglaucomatous eyes of 111 white subjects. On anterior-posterior histologic sections through the pupil and the central optic disc region, the thickness of the cornea, lamina cribrosa, and peripapillary sclera and the shortest distance between the intraocular space and the cerebrospinal fluid space were measured. Axial length ranged between 20 and 32 mm. RESULTS: Mean central corneal thickness (mean +/- SD: 616.6 +/- 108.3 microm) and mean central lamina cribrosa thickness (378.1 +/- 117.8 microm) were statistically independent of each other (P = 0.15; correlation coefficient, r = 0.14). In a similar manner, lamina cribrosa thickness at the optic disc border was statistically independent of central corneal thickness (P = 0.51; r = 0.06) and peripheral corneal thickness (P = 0.34; r = 0.09). In a parallel way, peripapillary scleral thickness (P = 0.84) and the shortest distance between the prelaminar space and cerebrospinal fluid space (P = 0.10) were statistically independent of central corneal thickness. CONCLUSIONS: In nonglaucomatous human globes, central corneal thickness may not correlate significantly with lamina cribrosa thickness, peripapillary scleral thickness, and shortest distance between intraocular space and cerebrospinal fluid space. Histologic artifact and sectioning methods could partially account for the lack of an association. The study results may suggest clinically that an assumed relationship between central corneal thickness and susceptibility to glaucoma cannot be explained by an anatomic correspondence between corneal thickness and histomorphometry of the optic nerve head.     

Corneal thickness in congenital glaucoma

PURPOSE: To compare central corneal thickness between eyes with congenital glaucoma and normal controls and to correlate this parameter with corneal diameter and axial length. METHODS: Eyes of consecutive children with congenital glaucoma with previous glaucoma surgery and eyes of children with inadequacy of lacrimal drainage system with age less than 3 years old were examined under inhalatory general anesthesia. Complete ophthalmologic examination, central corneal thickness, axial length, and corneal diameter measurements were performed. All patients presented with intraocular pressure (IOP) less than 21 mm Hg and no clinical sign of corneal edema. RESULTS: Fifty-five eyes of 55 patients (30 congenital glaucoma and 25 controls) were examined (mean age = 16.6 +/- 10.6 months; 20 female/ 35 males). There was no significant difference in age and gender between glaucoma patients and normal subjects. Mean IOP was higher in glaucomatous eyes (P = 0.02). Corneal diameter and axial length between glaucomatous eyes and controls were significantly different (P < 0.0001 for both). Central corneal thickness was significantly thinner in glaucomatous eyes (P = 0.01). There was a significant correlation between corneal diameter and central corneal thickness and also between central corneal thickness and axial length (r2 = 0.32 and r2 = 0.18, respectively; P < 0.0001 for both). CONCLUSION: Central corneal thickness was significantly thinner in children with congenital glaucoma. This finding may be another confounding factor when measuring IOP in those patients. Pachymetry should be considered during their examination.     

Central corneal pachymetry in patients undergoing laser in situ keratomileusis

OBJECTIVE: To report the preoperative ultrasonic central pachymetric measurements on a large group of eyes undergoing laser-assisted in situ keratomileusis (LASIK) surgery for myopia and myopic astigmatism, to determine whether central corneal thickness is correlated with other geometric features of the eye or is correlated with age or gender, and to discuss the resulting limitations on possible ablation depths. DESIGN: Prospective, multisite, cross-sectional study. PARTICIPANTS: Eight hundred ninety-six eyes in 450 patients from 21 to 66 years of age. MAIN OUTCOME MEASURES: Central corneal thickness and its correlation to intraocular pressure, corneal curvature, axial length, horizontal corneal diameter, refraction, age, and gender. RESULTS: The mean central corneal thickness was 550 microm with a standard deviation of 33 and a range of 472 to 651 microm. The lower 25th quantile was 528 microm. The central corneal pachymetry correlated with the mean manual keratometric measurement (P = 0.0001), simulated keratometry (Sim K) (P = 0.0001), and intraocular pressure (P = 0.0001). Central corneal thickness did not correlate with axial length, age, gender, horizontal corneal diameter, and refraction. CONCLUSION: This clinical study shows there is a substantial range of central corneal thickness in normal myopic eyes. With LASIK, there is a general concern that one should not thin the cornea further than a given amount. Because this study shows wide variability in central corneal thickness, it is prudent to measure pachymetry before surgery and gear treatment plans accordingly. Possible treatment limits relative to corneal thickness are discussed.     

Central corneal thickness correlated with glaucoma damage and rate of progression

PURPOSE: To evaluate whether the amount of glaucomatous optic nerve damage at presentation of the patient and the rate of progression of glaucoma during follow-up are related to central corneal thickness. METHODS: The prospective observational clinical study included 861 eyes of 454 white subjects (239 normal eyes of 121 subjects, 250 ocular hypertensive eyes of 118 patients, 372 eyes of 215 patients with chronic open-angle glaucoma). For 567 eyes (304 patients) with ocular hypertension or chronic open-angle glaucoma, follow-up examinations were performed, with a mean follow-up time of 62.7 +/- 33.2 months (median, 60.8; range, 6.2-124.9). All patients underwent qualitative and morphometric evaluation of color stereo optic disc photographs and white-on-white visual field examination. Central corneal thickness was measured by corneal pachymetry. RESULTS: Central corneal thickness correlated significantly (P < 0.001) and positively with the area of the neuroretinal rim and negatively with the loss of visual field. Development or progression of glaucomatous visual field defects detected in 119 (21.0%) eyes was statistically independent of central corneal thickness, in univariate (P = 0.99) and multivariate Cox regression analyses (P = 0.19). CONCLUSIONS: At the time of patient referral, the amount of glaucomatous optic nerve damage correlated significantly with a thin central cornea. Progression of glaucomatous optic nerve neuropathy was independent of central corneal thickness, suggesting that central corneal thickness may not play a major role in the pathogenesis of progressive glaucomatous optic nerve damage.     

应用三维光学相干断层成像术测量正常人脉络膜厚度及其影响因素的研究

目的　应用三维光学相干断层成像术测量正常人脉络膜厚度,并分析其相关影响因素。方法　应用三维光学相干断层成像术对６７位（１０６眼）正常人进行后极部脉络膜厚度的测量,软件自动测量并获得脉络膜厚度值。采用单变量和多变量回归分析脉络膜厚度与年龄、性别、眼轴长度、收缩期眼灌注压、舒张期眼灌注压、中央角膜厚度及眼压的关系。结果　正常人眼脉络膜厚度为（１７９．９±３６．１）μｍ。脉络膜厚度随着年龄的增加和眼轴的延长而变薄,呈高度线性负相关性（均为Ｐ＜０．０５）,多变量回归分析结果显示,年龄每增加１０ａ,脉络膜厚度平均下降８．６２μｍ,而眼轴长度每增加１ｍｍ,脉络膜厚度平均下降１２．７０μｍ。脉络膜厚度与性别、中央角膜厚度等因素无相关关系。结论　ＤＲＩＯＣＴ可定量检测正常人脉络膜厚度;正常人的脉络膜厚度与年龄和眼轴长度呈负相关。     

Cerebrospinal fluid pressure in ocular hypertension

Background: To assess the lumbar cerebrospinal fluid pressure (CSF‐P) in ocular hypertensive subjects with elevated intraocular pressure (IOP) but without development of glaucomatous optic nerve damage. Methods: The prospective interventional study included 17 patients with ocular hypertension and 71 subjects of a nonglaucomatous control group. All patients underwent a standardized ophthalmologic and neurological examination including measurement of lumbar CSF‐P. In the ocular hypertensive group, the IOP was corrected for its dependence on central corneal thickness (IOP_corrected). The trans‐lamina cribrosa pressure difference (Trans‐LCPD) was calculated as IOP_corrected ? CSF‐P. Results: CSF‐P was significantly (p < 0.001) higher in the ocular hypertensive group (16.0 ± 2.5 mmHg) than in the control group (12.9 ± 1.9 mmHg). CSF‐P was significantly associated with IOP_corrected (p < 0.001; r = 0.82). In multivariate analysis, CSF‐P was significantly correlated with IOP_corrected (p < 0.001) and marginally significantly with mean blood pressure (p = 0.05). Trans‐LCPD was not associated significantly with blood pressure (p = 0.69). Conclusion: Some ocular hypertensive subjects with increased intraocular pressure measurements (after correction for their dependence on central corneal thickness) had an abnormally high lumbar cerebrospinal fluid pressure. Assuming that lumbar cerebrospinal fluid pressure correlated with orbital cerebrospinal fluid pressure, one may postulate that the elevated retro‐lamina cribrosa pressure compensated for an increased intraocular pressure. The elevated retro‐lamina cribrosa pressure may have led to a normal trans‐laminar pressure difference in the eyes with elevated intraocular pressure, so that glaucomatous optic nerve damage did not develop. Intraocular pressure, cerebrospinal fluid pressure and arterial blood pressure were correlated with each other.     

Central corneal thickness in a healthy Spanish population

ObjectiveTo study the central corneal thickness of a Spanish population group and determine the influence of age, gender, axial length and refractive error on central corneal thickness (CCT) values.MethodsAn observational, cross-sectional, double masked study was conducted on 357 eyes of consecutive Caucasian patients without ophthalmic disease. They were distributed according to age, and high refractive defects were excluded. Ultrasonic pachymetry and a complete eye examination were performed on all patients. The relationship between the central corneal thickness values and variables of age, refractive error, axial length and gender was assessed.ResultsThe mean central corneal thickness was 548.21 μm with a standard deviation (SD) of 30.7 μm (range 464 to 633 μm). The normal central corneal thickness value of the population studied was 486.81 to 609.61 μm (95% confidence interval). No statistical association was found between central corneal thickness values and variables of age, refractive error, axial length and gender.ConclusionsCentral corneal thickness varies according to race. We have analysed, for the first time, normal central corneal thickness values of a healthy Spanish population.     

Association between stature, ocular biometry and refraction in an adult population in rural Myanmar: the Meiktila eye study

Purpose: To study the association between adult stature and ocular biometric parameters and refraction. Methods: In a population‐based cross‐sectional ophthalmic survey of 2418 adults (≥40 years old) living in the rural villages in central Myanmar, height and weight were measured using a standardized protocol, and body mass index was calculated. Non‐cycloplegic refraction and corneal curvature were determined by an autorefractor. Ultrasound pachymetry was performed and ocular biometry, including axial length, anterior chamber depth, lens thickness and vitreous chamber length were measured using A‐mode ocular ultrasonography. Results: Height and weight were significantly correlated with age, gender and all the ocular biometric parameters, except lens thickness. After adjusting for age and gender, taller and heavier persons had eyes with longer axial length, deeper anterior and vitreous chambers, and flatter and thicker corneas than shorter persons. Height was not significantly correlated with refraction, and heavier persons tended to be less myopic (P < 0.001). Multivariate linear regression models revealed consistent results with the findings for association between height, weight and ocular biometry and refractive error. Conclusions: Adult stature is independently associated with vitreous chamber length and corneal radius in this Burmese population. Heavier persons were slightly hyperopic.     

Lamina cribrosa thickness is not correlated with central corneal thickness or axial length in healthy eyes

Background

The aim of this study was to determine the relationship of the central corneal thickness (CCT) and axial length (AXL) with the central lamina cribrosa thickness (LCT) in healthy human eyes.

Methods

This was a prospective observational case series. The optic discs of 189 eyes from 100 healthy subjects with a refractive error smaller than ?8 diopters were scanned using enhanced-depth imaging spectral-domain optical coherence tomography (Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany). The thickness of the lamina cribrosa (LC) was measured on B-scan images obtained at the center of the optic nerve head. A linear mixed-effects model was used to determine the factors associated with LCT, taking into account clustering of eyes within subjects.

Results

The thickness of the central LC was 273.19?±?34.74 μm (mean ± SD; range, 173.73–367.94 μm). Multivariate analysis revealed a significant influence of older age on increased central LCT (p?=?0.001). There was no significant association between central LCT and either CCT or AXL.

Conclusions

In this study, the central LCT increased significantly with older age in healthy human eyes. Neither CCT nor AXL was significantly associated with the central LCT in healthy human eyes with a spherical equivalent within the range from ?7.0 to +3.0 diopters.     

Thickness of the lamina cribrosa and peripapillary sclera in Rhesus monkeys with nonglaucomatous or glaucomatous optic neuropathy

Purpose: To measure the thickness of the lamina cribrosa and peripapillary sclera in monkeys with a nonglaucomatous optic nerve damage and to compare that with those of monkeys with glaucomatous optic neuropathy. Methods: The study included 22 monkey eyes (Macaca mulatta) which had undergone a temporary experimental central retinal artery occlusion (CRAO) and seven monkey eyes in which experimental glaucoma was unilaterally produced. We measured histomorphometrically the thickness of the lamina cribrosa and peripapillary sclera. Results: The lamina cribrosa was significantly thicker in the CRAO group than in the glaucoma group (central region: 212 ± 46 μm versus 167 ± 17 μm; p = 0.009). The thickness of the peripapillary sclera at the optic disc border (253 ± 39 μm versus 192 ± 21 μm; p = 0.001) and outside of the optic nerve meninges (408 ± 70 μm versus 314 ± 64 μm; p = 0.006) was significantly greater in the CRAO group. Conclusions: In monkey eyes with a temporary CRAO as a model for nonglaucomatous optic nerve damage, the lamina cribrosa is significantly thicker than in monkey eyes with experimental glaucomatous optic nerve damage. It may suggest that the loss of optic nerve fibres might not be the reason for the thinning of the lamina cribrosa in eyes with advanced glaucoma. The thinner peripapillary sclera in the glaucomatous eyes may suggest that the monkey sclera is more vulnerable to stretching with increased intraocular pressure than the human eye for which no glaucoma‐related lengthening of the eyeball and thinning of the peripapillary sclera have been observed.     

年龄相关性白内障患者眼轴和角膜曲率对角膜生物力学的影响

目的：探讨应用可视化角膜生物力学分析仪(corneal visualization Scheimpflug technology,Corvis ST)研究不同眼轴长度(axial length,AL)和角膜曲率的老年人角膜生物力学特点。

方法：横断面研究。收集拟接受白内障手术的患者161例297眼,将研究对象按AL值的不同进行分组：22～24mm者190眼,24～26mm者54眼,>26mm者53眼。将AL为22～24mm、K值42～44D之间的研究对象按性别进行分组,男44眼,女44眼; 对AL为22～24mm的研究对象按K值的不同分组：42～44D者88眼,>44D者102眼; 应用可视化角膜生物力学分析仪(Corvis ST)测量角膜生物力学参数,并对不同性别、不同眼轴、不同角膜曲率患者的角膜生物力学参数进行比较性分析,采用单因素方差分析、独立样本t检验等对数据进行统计,并分析各组生物力学参数间的相关性。

结果：男女之间角膜生物力学参数比较,差异无统计学意义(P>0.05),不同角膜曲率间只有第一压平长度、第二压平长度比较,差异有统计学意义(P<0.05)。不同眼轴长组间：第二压平速度、最大形变幅度、中央角膜厚度、眼压的组间比较,差异有统计学意义(P<0.05)。眼轴与最大形变幅度及眼压呈线性正相关(r=0.429、0.278,P<0.001),与中央角膜厚度、第二压平速度呈线性负相关(r=-0.291、-0.415,P<0.001)。

结论：角膜曲率和AL可能是使角膜力学属性发生改变的角膜相关参数,角膜厚度会随着眼轴的增长呈现变薄的趋势,角膜也较容易发生形变,而且眼压也会随着眼轴的增长而逐渐增高。     

中央角膜厚度对非接触式眼压计测量值的影响

目的 探讨中央角膜厚度（central corleal thickness,CCT）对非接触式眼压计测量值的影响及CCT与某些眼部参数的关系.方法 应用超声测厚仪测量正常人（26例）、高眼压症（28例）、慢性闭角型青光眼（13例）和原发性开角型青光眼（24例）患者的CCT,同时测量以上入选者的眼内压（intraocular pressure,IOP）、眼轴长度、角膜曲率及屈光度,观察CCT与各参数之间的关系.结果 正常组的眼内压与CCT存在正相关关系（Pearson r=0.499,P=0.009）,CCT与眼轴长度（Pearson r=0.157,P=0.137）、屈光度（球镜）（Pearson r=-0.114,P=0.282）及角膜曲率（水平径 Pearson r=-0.167,P=0.114 垂直径 Pearson r=-0.034,P=0.746）不相关.结论 CCT与眼轴长度、屈光度（球镜）及角膜曲率不相关,在正常对照组与眼内压呈正相关.     

Correlation between refraction and ocular biometry

PURPOSE: To study the correlation between subjective refraction and biometry obtained by Orbscan and echography in normal eyes. To compare biometric parameters with the subjective spherical equivalent. MATERIAL AND METHODS: Subjective refraction, biometric parameters using Orbscan, and echography were recorded in 190 normal eyes (including eyes with ametropia) of 95 patients. Biometric parameters (i.e., corneal diameter, anterior chamber depth, central pachymetry, iridocorneal angle, corneal and lens radii of curvature, and axial length of the eye) were compared in different refractive groups and were correlated with the subjective refraction. RESULTS: Corneal biometric parameters did not correlate with the subjective spherical equivalent and showed no differences between the refractive groups except for the central pachymetry. In the high myopic group (<-6D), the central cornea was significantly thinner (531 micro m versus 549 micro m, p=0.016). The correlation between corneal radius and axial length was strong in emmetropic eyes (r(s)=0.63, p<0.001) and poor but significant in ametropic eyes (r(s)=0.28, p=0.002). Axial length, anterior chamber depth, and iridocorneal angle showed significant differences between the refractive groups (p<0.001) and correlated with the subjective spherical equivalent (r(s[[/INF=0.44, p<0.001). Subjective spherical equivalent showed the strongest correlation with the axial length (rs)=0.82, p<0.001). Subjective spherical equivalent, central corneal thickness, axial length, anterior chamber depth, and anterior corneal radius showed a strong correlation between both eyes (rs[[/INF=0.94, p<0.001). CONCLUSION: Biometric characteristics of the eye (excluding cornea characteristics) vary with subjective spherical equivalent. Axial length presents the strongest correlation with the subjective spherical equivalent and correlates with the other ocular biometric parameters. Axial length plays a major role in the ocular biometry and refraction.     

Lamina cribrosa thickness and spatial relationships between intraocular space and cerebrospinal fluid space in highly myopic eyes

PURPOSE: To evaluate the spatial relationships of the intraocular space, the cerebrospinal fluid space, and the lamina cribrosa in highly myopic eyes. METHODS: The study included 36 human globes with an axial length of more than 26.5 mm that showed marked glaucomatous optic nerve damage (n = 29; highly myopic glaucomatous group) or in which the optic nerve was affected by neither glaucoma nor any other disease (n = 7; highly myopic normal group). Two non-highly myopic control groups included 53 globes enucleated because of malignant choroidal melanoma (n = 42; non-highly myopic normal group) or because of painful absolute secondary angle-closure glaucoma (n = 11; non-highly myopic glaucomatous group). Anterior-posterior histologic sections through the pupil and the optic disc were morphometrically evaluated. RESULTS: In both highly myopic groups compared with both non-highly myopic groups and in the highly myopic glaucomatous group compared with the highly myopic normal group, the lamina cribrosa was significantly (P < 0.001) thinner. Correspondingly, the distance between the intraocular space and the cerebrospinal fluid space was significantly (P < 0.05) shorter in the highly myopic normal group than in the non-highly myopic normal group and in the highly myopic glaucomatous group than in the highly myopic normal group. CONCLUSIONS: In highly myopic eyes, the lamina cribrosa is significantly thinner than in non-highly myopic eyes, which decreases the distance between the intraocular space and the cerebrospinal fluid space and steepens the translaminar pressure gradient at a given intraocular pressure, which may explain the increased susceptibility to glaucoma in highly myopic eyes. As in non-highly myopic eyes, thinning of the lamina cribrosa gets more pronounced in highly myopic eyes if glaucoma is also present.     

Anatomic relationship between lamina cribrosa, intraocular space, and cerebrospinal fluid space

PURPOSE: The lamina cribrosa, as the main structural element of the optic nerve head, forms a pressure barrier between the intraocular space and the retrobulbar space. The function as a pressure barrier may have importance for the pathogenesis of ocular diseases related to intraocular pressure and/or cerebrospinal fluid (CSF) pressure, such as the glaucomas. The purpose of the present study was to examine the anatomic relationship between the lamina cribrosa, the intraocular pressure space, and the retrobulbar cerebrospinal pressure space in eyes with glaucoma. METHODS: The study included 53 globes enucleated because of malignant choroidal melanoma (n = 42) without involvement of the optic nerve (control group) or because of painful absolute secondary angle-closure glaucoma (n = 11; glaucoma group). Anterior-posterior histologic sections through the pupil and the optic disc were morphometrically evaluated. RESULTS: In the glaucoma group compared with the control group, the lamina cribrosa was significantly (P < 0.001) thinner, the part of the outer lamina cribrosa surface directly exposed to the pia mater and indirectly exposed to the CSF space was significantly (P = 0.001) wider, and the shortest distance between the intraocular space and the CSF space was significantly (P < 0.001) shorter. The posterior lamina cribrosa surface in direct contact with the pia mater was located close to the optic disc border. CONCLUSIONS: The thickness of the lamina cribrosa and the anatomic relationships between the intraocular space and the CSF space differ significantly between normal and glaucomatous eyes. The findings may be of importance for the pathogenesis of glaucomatous optic neuropathy.     

Central corneal thickness, lamina cribrosa and peripapillary scleral histomorphometry in non-glaucomatous chinese eyes

Background  

To examine a potential correlation between a thin cornea, a thin lamina cribrosa and a thin peripapillary sclera in normal eyes of Chinese, as surrogate for a presumed association between a thin cornea and an increased glaucoma susceptibility.     

Central corneal thickness, tonometry, and ocular dimensions in glaucoma and ocular hypertension.

PURPOSE: To assess possible correlations between central corneal thickness, tonometry, and ocular dimensions. PATIENTS AND METHODS: One hundred seventeen eyes of 117 patients who were not taking any intraocular pressure-lowering medications were studied prospectively. Forty-one patients had ocular hypertension; 13 patients had primary open-angle glaucoma; and 10 patients had normal-pressure glaucoma. Twenty-three healthy eyes were included. Thirty glaucoma suspects (10 patients monitored for possible normal-pressure glaucoma and 20 patients with intermittent ocular hypertension) were included for correlation analysis. Tonometry was performed with Goldmann applanation and pneumotonometry, and central corneal thickness, anterior chamber depth, lens thickness, and axial length were measured ultrasonically. RESULTS: Central corneal thickness was lowest in eyes with normal-pressure glaucoma (538 +/- 51 microm), highest in eyes with ocular hypertension (570 +/- 32 microm), and intermediate and similar in eyes with primary open-angle glaucoma and healthy eyes (547 +/- 34 microm and 554 +/- 32 microm, respectively). These differences were significant (P = 0.028). Goldmann applanation tonometry and central corneal thickness were weakly correlated (r = 0.12, P = 0.205), with a 0.2-mm Hg change per 10-microm variation in central corneal thickness. Pneumotonometry measurements were more strongly correlated with central corneal thickness (r = 0.21, P < 0.05). Lens thickness was strongly correlated with age (r = 0.57, P < 0.001). Anterior chamber depth was negatively correlated with lens thickness and age (r = -0.29, P < 0.005 and r = -0.25, P < 0.01). Axial length was correlated with anterior chamber depth and age (r = 0.5, P < .001 and r = -0.19, P < 0.05). CONCLUSION: Eyes diagnosed as having ocular hypertension have thicker corneas and eyes labeled as having normal-pressure glaucoma have thinner corneas, when compared with healthy eyes or eyes with primary open-angle glaucoma. The effect of central corneal thickness on Goldmann applanation tonometry accuracy appears to be small and usually not clinically relevant. When corneal thickness is markedly different from normal, the clinician may need to factor this into diagnosis and management.     

Influence of corneal structure, corneal responsiveness, and other ocular parameters on tonometric measurement of intraocular pressure

PURPOSE: To estimate the relationships between ocular parameters and tonometrically measured intraocular pressure (IOP), to determine the influence of ocular parameters on different instrument measurements of IOP, and to evaluate the association of ocular parameters with a parameter called hysteresis. METHODS: Patients presenting at a glaucoma clinic were recruited for this study. Subjects underwent IOP measurement with the Goldmann applanation tonometer (GAT), the TonoPen, and the Reichert Ocular Response Analyzer (ORA), and also measurements of central corneal thickness (CCT), axial length, corneal curvature, corneal astigmatism, central visual acuity, and refractive error. Chart information was reviewed to determine glaucoma treatment history. The ORA instrument provided a measurement called corneal hysteresis. The association between measured IOP and the other ocular characteristics was estimated using generalized estimating equations. RESULTS: Among 230 patients, IOP measurements from the TonoPen read lowest, and ORA read highest, and GAT measurements were closest to the mean IOP of the 3 instruments. In a multiple regression model adjusting for age, sex, race, and other ocular characteristics, a 10 microm increase in CCT was associated with an increase of 0.79 mm Hg measured IOP in untreated eyes (P<0.0001). Of the 3 tonometers, GAT was the least affected by CCT (0.66 mm Hg/10 mum, P<0.0001). Hysteresis was significantly correlated with CCT with a modest correlation coefficient (r=0.20, P<0.0007). CONCLUSIONS: Among parameters related to measured IOP, features in addition to CCT, such as hysteresis and corneal curvature, may also be important. Tonometric instruments seem to be affected differently by various physiologic characteristics.     

Central corneal thickness in congenital glaucoma

PURPOSE: The aim of this study was to compare central corneal thickness between eyes with congenital glaucoma and normal fellow eyes in unilateral glaucoma or less affected fellow eyes in bilateral glaucoma. METHODS: Eyes of consecutive phakic children with congenital glaucoma and previous glaucoma surgery were examined under chloral hydrate. Complete ophthalmologic examination, central corneal thickness (CCT), axial length, and corneal diameter measurements were performed. Patients were included in the study if presented with intraocular pressure (IOP) less than 21 mm Hg and no biomicroscopic signs of corneal edema. RESULTS: Nine patients were included in the study. The mean CCT in the more affected eye/glaucomatous eye was 522.3 +/- 65.2 microm and in the less affected eye/healthy eye was 579.7 +/- 44.5 microm. This difference was statistically significant (P = 0.0013). CONCLUSION: CCT was significantly thinner in glaucomatous eyes than in normal fellow eyes in phakic children with congenital glaucoma. This finding may be another confounding factor when measuring IOP in these patients.     

Ethnic Variation in Central Corneal Refractive Power and Steep Cornea in Asians

Abstract

Purpose: To describe ethnic differences in the distribution of central corneal refractive power and steep cornea in a multiethnic Asian population.

Methods: A total of 2968 Chinese, 2957 Indian and 2928 Malay participants aged over 40 years were included in this study. Each subject underwent standardized systematic and ocular examinations, interviewer-administered questionnaires, and blood investigations for risk factor assessment. Central corneal refractive power was measured using an autorefractor. Steep cornea was defined as central corneal refractive power exceeding 48 diopters (D) measured by keratometry.

Results: Mean keratometry readings were 43.9?±?1.5?D in Malays, 44.2?±?1.5?D in Indians and 43.9?±?1.5?D in Chinese. The prevalence of steep cornea was 0.6% (95% confidence interval, CI, 0.3–0.9%) in Malays, 1.0% (95% CI 0.7–1.4%) in Indians and 0.5% (95% CI 0.3–0.8%) in Chinese. In multivariate analysis, increasing central corneal refractive power was associated with Indian race, shorter body height, non-smokers, absence of pterygium, shorter axial length, thinner corneas and greater anterior chamber depth, while the presence of steep cornea was significantly associated with Indian race, shorter axial length and thinner corneas.

Conclusions: Indian participants had the steepest corneas among the three major ethnic groups in Singapore. Central corneal refractive power was related to several ocular parameters including anterior chamber depth, axial length and central corneal thickness. These data have important clinical implications for understanding the risk of keratoconus.