Intraocular pressure, Goldmann applanation tension, corneal thickness, and corneal curvature in Caucasians, Asians, Hispanics, and African Americans

PURPOSE: This is to investigate whether there are differences in Goldmann applanation tonometry (GAT), central corneal thickness, and corneal curvature among four racial groups. If differences are present, they may alter GAT reading, diagnosis, and management of glaucoma in the population. DESIGN: Observational retrospective cross-sectional study. METHODS: Charts of patients who have had keratorefractive surgery were examined. Central corneal thickness, corneal curvature, refractive power, and GAT were measured in 1482 Caucasian, 172 Asian, 204 Hispanic, and 118 African-American eyes (total 1976 eyes). Refractive components and GAT were compared. We compared intraocular pressure (IOP) adjusted by GAT, central corneal thickness, and corneal curvature among the four groups. RESULTS: There was a statistically significant difference between the mean (+/- standard deviation) central corneal thickness of African American (535.46 +/- 33.39) and Caucasian (552.59 +/- 34.48) eyes. Mean central corneal thickness was near 550 microm in Caucasians, Asians, and Hispanics. No significant difference was noted in corneal curvature in the four groups. There was a significant correlation between central corneal thickness and corneal curvature, and GAT was similar among the four groups. When IOP was adjusted for central corneal thickness, it was significantly greater in African Americans (16.12 +/- 3.27) than in Caucasians (14.32 +/- 2.93). Corneas of women were significantly thinner than corneas of men. CONCLUSIONS: African Americans had significantly thinner central corneal thickness than Caucasians, Asians, or Hispanics, causing the underreading of true IOP. Significant correlation between central corneal thickness and corneal curvature was demonstrated. Uncorrected GAT underreading of African Americans may lead to delay in diagnosis, inadequate treatment target setting, and higher morbidity. Goldmann applanation tonometry needs to be corrected by central corneal thickness and corneal curvature for proper diagnosis and management of glaucoma.     

Corneal thickness measurements and visual function abnormalities in ocular hypertensive patients

PURPOSE: It has been suggested that a considerable subset of patients currently classified as having ocular hypertension may have thicker than average corneas that result in an overestimation of the true intraocular pressure (IOP). As a consequence, ocular hypertension patients with greater corneal thickness may be at a lower risk for functional damage, such as that detected by short-wavelength automated perimetry (SWAP). The purpose of this study was to evaluate the frequency of SWAP deficits in ocular hypertension patients and to correlate these findings with corneal thickness measurements in the same patients. DESIGN: Cross-sectional observational study. METHODS: Sixty-eight ocular hypertension patients with normal optic disks and 63 normal subjects were included in the study. All participants underwent standard automated perimetry (SAP), SWAP, and central corneal thickness measurements using ultrasound pachymeter. Central corneal thickness measurements in ocular hypertension patients with abnormal visual field test results were compared with central corneal thickness measurements in ocular hypertension patients with normal visual field results. In addition, central corneal thickness measurements in ocular hypertension patients were compared with central corneal thickness measurements in normal subjects. RESULTS: Sixteen of 68 patients with ocular hypertension (24%) demonstrated SWAP abnormalities, whereas four of 68 (6%) showed a deficit on SAP. The mean central corneal thickness in ocular hypertension patients with abnormal SWAP results was significantly lower than the mean central corneal thickness in ocular hypertension patients with normal SWAP results (545 +/- 25 microm vs 572 +/- 35 microm; P =.006). The mean central corneal thickness in the normal group was 557 +/- 33 microm. The mean central corneal thickness in ocular hypertension patients with normal SWAP results was significantly higher than in normal subjects (P =.02). There was no significant difference between mean central corneal thickness in normal subjects and in ocular hypertension patients with abnormal SWAP results (P =.19). CONCLUSIONS: The patients classified as having ocular hypertension but with visual field loss detected by SWAP had significantly lower central corneal thickness measurements than the ocular hypertension patients with normal visual field results. These results suggest that central corneal thickness should be taken into account when assessing risk for the development of glaucomatous damage among ocular hypertension patients.     

Pediatric central corneal thickness variation among major ethnic populations.

PURPOSE: To investigate differences in central corneal thickness (CCT) among African-American, Caucasian, and Hispanic pediatric populations with respect to race, age, and gender. SUBJECTS AND METHODS: Ultrasound pachymetry measurements were obtained on 208 eyes of 106 patients. Measurements from left eyes were used in data analysis. Analysis of variance (ANOVA) and two-tailed t-test were performed to determine the effect of race, age, and gender on CCT variation. RESULTS: Mean central corneal thickness of left eyes in each ethnic group was African-Americans, 523 +/- 40 microm; Caucasians, 563 +/- 36 microm; and Hispanics, 568 +/- 44 microm. ANOVA performed on pachymetry values showed a significant effect of race on CCT (P = 0.00002). Mean Hispanic CCT was greater than mean African-American CCT (P = 0.0003), but was not significantly different from Caucasian CCT (P = 0.56). Mean Caucasian CCT was also greater than mean African-American CCT (P = 0.0001). The difference between mean male CCT (548 +/- 41 microm) and mean female CCT (563 +/- 44 microm) did not reach statistical significance (P = 0.07). When patients were stratified into age groups (<2 years, 2 to 4 years, 5 to 9 years, 10 to 18 years), CCT did not vary with age (P = 0.16). CONCLUSIONS: Our study suggests there may be differences in CCT among different ethnic groups in the pediatric population, with African-Americans having thinner corneas than Caucasians and Hispanics.     

Central corneal thickness in low-tension glaucoma

BACKGROUND: It is possible that the intraocular pressure (IOP) is underestimated in eyes whose central cornea is thinner than normal. The objective of this study was to determine and establish the significance of central corneal thickness in patients with low-tension (normal-tension) glaucoma compared with those with chronic open-angle glaucoma (COAG) or ocular hypertension and healthy eyes. METHODS: The study was carried out from February 1998 to May 1999. Central corneal thickness was measured by ultrasonic pachymetry and IOP was measured by Goldmann applanation tonometry in 25 patients with low-tension glaucoma (untreated IOP less than 21 mm Hg with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 80 patients with COAG (untreated IOP 21 mm Hg or greater with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 16 patients with ocular hypertension (untreated IOP 21 mm Hg or greater, with normal optic nerve head and no history of glaucoma or elevated IOP, and normal visual field on automated perimetry) and 50 control subjects (untreated IOP less than 21 mm Hg with normal optic nerve head and no history of glaucoma or elevated IOP). Analysis with Pearson's product-moment correlation was performed to determine the correlation of IOP and central corneal thickness, and one-way analysis of variance was used to compare corneal thickness between groups. RESULTS: The central cornea was significantly thinner in the low-tension glaucoma group (mean 513.2 mu [standard deviation (SD) 26.1 mu]) than in the COAG group (mean 548.2 mu [SD 35.0 mu]) and the control group (mean 556.7 mu [SD 35.9 mu]) (p < 0.001). No significant difference in corneal thickness was found between the COAG and control groups. The ocular hypertension group had significantly thicker corneas (mean 597.5 mu [SD 23.6 mu]) than the three other groups (p < 0.001). INTERPRETATION: Patients with low-tension glaucoma may have thinner corneas than patients with COAG and healthy subjects. This results in underestimation of their IOP. Corneal thickness should be taken into account when managing these patients to avoid undertreatment.     

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 thickness in children: Racial differences (black vs. white) and correlation with measured intraocular pressure

PURPOSE: To test the hypotheses that the mean central corneal thickness (CCT) of healthy black children is thinner than that of healthy white children and to confirm the relationship between increased CCT and measured intraocular pressure (IOP) in children. METHODS: This prospective observational case series included 178 eyes of 92 children aged 9 months to 17 years without anterior segment abnormalities or a clinical diagnosis of glaucoma. CCT was measured by ultrasonic pachymetry and IOP was measured by Goldmann or Tono-pen technique. RESULTS: The mean CCT for the 102 eyes of 52 white children was 562+/-35 microm versus 543+/-37 microm for the 66 eyes of 35 black children (P = 0.02). There was a positive relationship between CCT and IOP (P = 0.0002). For every 100 mum increase in CCT, the IOP increased by 2.2+/-0.6 mm Hg. CONCLUSIONS: The mean CCT of black children is thinner than that of white children. There is a positive relationship between increasing measured IOP and CCT among children with normal corneas and anterior segments. The interpretation of elevated IOP in eyes with abnormal anterior segment anatomy and thickened corneas awaits further study.     

Central corneal thickness determined with optical coherence tomography in various types of glaucoma

AIMS: To evaluate central corneal thickness determined by optical coherence tomography (OCT) in various types of glaucoma, and its influence on intraocular pressure (IOP) measurement. METHODS: Central corneal thickness (CCT) was determined by using OCT in 167 subjects (167 eyes). 20 had primary open angle glaucoma (POAG), 42 had low tension glaucoma (LTG), 22 had ocular hypertension (OHT), 10 had primary angle closure glaucoma (AC), 24 had pseudoexfoliation glaucoma (PEX), 13 had pigmentary glaucoma (PIG), and 36 were normal. RESULTS: CCT was significantly higher in ocular hypertensive subjects (593 (SD 35) microm, p <0.0001) than in the controls (530 (32) microm), whereas patients with LTG (482 (28) microm, p < 0. 0001), PEX (493 (33) microm, p <0.0001), and POAG (512 (30) microm, p <0.05) showed significantly lower readings. There was no statistically significant difference between the controls and patients with PIG (510 (39) microm) and AC (539 (37) microm). CONCLUSIONS: Because of thinner CCT in patients with LTG, PEX, and POAG this may result in underestimation of IOP, whereas thicker corneas may lead to an overestimation of IOP in subjects with OH. By determining CCT with OCT, a new and precise technique to measure CCT, this study emphasises the need for a combined measurement of IOP and CCT in order to obtain exact IOP readings.     

Pachymetry of donor corneas: effect of ethnicity and gender on central corneal thickness

PURPOSE: To examine demographic differences associated with the central corneal thickness (CCT) of donor corneas and to investigate whether these differences confirmed previous clinical studies. METHODS: CCT was prospectively measured using noncontact pachymetry among 704 eye bank corneas. The effects of gender, ethnicity, age, cause of death, times until preservation and evaluation, and endothelial cell density and morphometry on CCT were examined. RESULTS: The CCT of black women was significantly thinner (P = 0.05) than that of other corneal donors. The average CCT +/- SD of black women was 530 +/- 35.9 microm, whereas those of white and Hispanic women were 554 +/- 59.1 microm and 556 +/- 51.2 microm, respectively. Average values for black, white, and Hispanic men were 553 +/- 44.7 microm, 551 +/- 53.4 microm, and 543 +/- 50.4 microm, respectively. Age and cause of death did not significantly affect CCT. CONCLUSION: Gender may modify racial differences of CCT. Measurements using donated corneal tissues support pachymetric differences by ethnic origin, although this finding was limited to female donors only.     

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.     

Falsely elevated intraocular pressure due to increased central corneal thickness

· Purpose: To evaluate whether ocular hypertensive subjects have a higher central corneal thickness than other individuals. · Methods: In this prospective study, 48 subjects with ocular hypertension, 63 patients with open-angle glaucoma, 56 nonglaucomatous patients with diabetes mellitus, and 106 control subjects were evaluated. Corneal thickness was measured by ultrasound pachymetry, and intraocular pressure was determined by Goldmann applanation tonometry. · Results: Central corneal thickness was significantly higher in the ocular hypertensive subjects, mean ±S.D., 592±39 μm, than in the patients with glaucoma (536±34 μm), the nonglaucomatous patients with diabetes mellitus (550±31 μm), and the normal subjects (545±33 μm), P<0.001. The three latter groups did not vary significantly in central corneal thickness, P>0.05. · Conclusion: In some individuals with increased transcorneal measurements of intraocular pressure, the cornea is thicker than in subjects with normal intraocular pressure readings or patients with glaucoma. It suggests that in ocular hypertensive subjects, corneal pachymetry should be performed to rule out an abnormally thick cornea as a reason for falsely high measurements of intraocular pressure. Received: 14 April 1998 Revised version received: 10 July 1998 Accepted: 23 July 1998     

Central corneal thickness and measured IOP response to topical ocular hypotensive medication in the Ocular Hypertension Treatment Study

PURPOSE: To determine whether central corneal thickness (CCT) correlates with measured intraocular pressure (IOP) response to topical ocular hypotensive medication in the Ocular Hypertension Treatment Study (OHTS). DESIGN: Prospective randomized clinical trial. METHODS: Intraocular pressure measurements were performed by Goldmann applanation tonometry. Central corneal thickness was measured by ultrasonic pachymetry. The following indicators of IOP response to topical ocular hypotensive medication were examined: (1) IOP after an initial four- to six-week one-eyed therapeutic trial of a nonselective beta-blocker (N = 549) or a prostaglandin analog (N = 201); (2) the mean IOP response during 12 to 60 months of follow-up among medication participants (N = 689); (3) the percentage of follow-up visits at which both eyes met the treatment goal; (4). the total number of different medications prescribed to reach treatment goal; and (5) the total number of different medications prescribed multiplied by the number of months each medication was prescribed. RESULTS: Central corneal thickness was inversely related to the IOP response after the initial one-eyed therapeutic trial and during 12 to 60 months of follow-up (P < .05). Mean CCT was not correlated with the number of different medications prescribed during follow-up, the total medication-months, or the percentage of visits at which IOP target was met. CONCLUSIONS: Individuals with thicker corneas had smaller measured IOP responses to ocular hypotensive medication than those with normal or thin corneas. We believe that CCT measurements may be useful in patient management and in interpreting clinical trials of ocular hypotensive medication.     

Central corneal thickness in children with congenital glaucoma

PURPOSE: To evaluate central corneal thickness in children with congenital glaucoma. MATERIAL AND METHODS: Central corneal thickness was measured with the use of ultrasound pachymeter in 49 eyes of 30 children, with congenital glaucoma aged 0-12 years. RESULTS: Mean central corneal thickness was 462 microm. Very wide differences between minimum and maximum recorded values were observed (380-780 microm). Three groups of patients could be distinguished: with very thin cornea of 380-450 microm (73% children), with normal corneal thickness of about 550 microm (15%) and with very thick cornea of 680-780 microm (12% patients). CONCLUSIONS: 1. Mean central corneal thickness in children with congenital glaucoma is significantly thinner than in healthy children in the same age and in adult patients with glaucoma. A very wide differences between minimum and maximum recorded values, are observed in these patients. 2. The results of applanation tonometric measurements are underestimated in most cases or less frequently overestimated. 3. The measurements of central corneal thickness should be performed in every patient with congenital glaucoma to correct the IOP values.     

Cataract surgery for congenital cataract: endothelial cell characteristics, corneal thickness, and impact on intraocular pressure.

PURPOSE: To investigate whether central corneal thickness (CCT), endothelial cell characteristics, and intraocular pressure (IOP) are affected in patients with previous congenital cataract surgery and to focus on their clinical significance. METHODS: CCT and IOP measurements and specular microscopy were performed in 31 eyes of 17 cases of extracted congenital cataracts and 40 eyes of 20 age- and sex-matched participants as control group. The mean of three pachymetry measurements of the central cornea was taken as CCT. IOP was checked using an applanation tonometer. RESULTS: The mean corneal thickness of the eyes with extracted congenital cataract (632+/-45 microm) was significantly greater than that of the control eyes (546+/-33 microm; p<0.001). There was no significant difference in the corneal endothelial cell count, coefficient of variation (CV), and mean cell area (AVG) of endothelial cells between operated eyes and the control group. The mean measured IOP in the operated group (22.8+/-3.3 mm Hg) was significantly greater than IOP in controls (14.1+/-1.8 mm Hg, p<0.001). CONCLUSIONS: Although the corneas were clinically clear and there was no significant difference in endothelial characteristics of eyes with extracted congenital cataract and controls, central corneas of operated eyes were significantly thicker than those of controls. To differentiate the actual glaucoma from ocular hypertension in these patients, the central corneal thickness measurement should strongly be considered.     

Factors affecting the central corneal thickness of Hong Kong-Chinese.

PURPOSE: The aims of this study were to investigate the effect of age, intraocular pressure, refractive error (spherical equivalent) and corneal curvatures on the central corneal thickness of Hong Kong-Chinese. We also compared the central corneal thickness of Hong Kong-Chinese with those previously reported for other national/ethnic groups. METHODS: The central corneal thicknesses of 151 subjects of age 10-60 yrs were measured using an ultrasound pachometer. Intraocular pressure, refractive error and the corneal curvatures of these subjects were also recorded. RESULTS: The mean +/- SD central corneal thickness of the right eye and left eye were 575 +/- 32 microm and 574 +/- 31 microm respectively. No significant difference in central corneal thickness was found between the right and left eyes or between male and female subjects. Central corneal thickness decreased with increasing age but the effect appeared to be due to differences in female subjects only. The maximum decrease in central corneal thickness occurred in subjects in the age group of 10-25 yrs, and in this age group, central corneal thickness and age was significantly correlated in both male and female subjects. Intraocular pressure and central corneal thickness was significantly correlated. There was no correlation between central corneal thickness and refractive error or between central corneal thickness and corneal curvatures. CONCLUSIONS: Central corneal thickness decreased with increasing age but this appeared to be due to female subjects only. Central corneal thickness was significantly correlated with intraocular pressure, but not with refractive error or corneal curvatures. Our subjects also had significantly thicker corneas than those reported for Caucasian subjects.     

Central corneal thickness of normal tension glaucoma patients in Japan

PURPOSE: To compare central corneal thickness (CCT) of patients with normal tension glaucoma (NTG) with that of age-matched normal subjects, patients with open-angle glaucoma (POAG) and ocular hypertension (OH) subjects in Japan. METHODS: Central corneal thickness was measured in 79 NTG, 61 POAG, 73 OH, and 50 normal subjects with an ultrasonic pachymeter. One eye for 1 subject randomly selected in each group was used for inter-group comparison. The relationship between CCT and the maximum intraocular pressure (IOP) measured by Goldmann applanation tonometer with no ocular hypotensive medication (NTG, OH, and normal subjects) or under medication (POAG patients) was analyzed. RESULTS: The CCT of OH subjects (582 +/- 32 microm; mean +/- SD) was significantly greater than that of the other groups (P <.001), while no difference was seen in CCT among normal (552 +/- 36 microm), NTG (548 +/- 33 microm) and POAG (550 +/- 33 microm) subjects. In normal subjects, CCT and the maximum IOP were significantly correlated but the correlation coefficient was small (r = 0.420, P <.05). CONCLUSIONS: Central corneal thickness shows no significant difference among NTG, POAG, and normal subjects in Japan, while it is significantly greater in OH subjects. The CCT has little influence on the diagnosis of NTG in Japan.     

相干光断层扫描仪检测正常人及青光眼患者中央角膜厚度

目的探讨相干光断层扫描仪(OCT)测量正常人、原发性开角型青光眼(POAG)、正常眼压性青光眼(NTG)、高眼压症(OHT)患者的中央角膜厚度(CCT)。方法采用OCT3测量正常人143例(143只眼)、POAG患者36例(36只眼)、NTG患者39例(39只眼)及OHT患者40例(40只眼)的CCT,并进行单因素4水平设计定量资料的方差分析;用线性回归方法分析正常人CCT与Goldmann压平眼压测量值的相关关系;对OCT测量CCT观察者间和观察者内的一致性进行类内相关系数(ICC)分析。结果正常组、POAG组、NTG组及OHT组的平均CCT值分别为(523.66±32.13)μm、(530.92±27.32)μm、(506.92±21.49)μm及(573.13±27.39)μm。POAG组与正常人组的平均CCT值差异无统计学意义(P=0.099);OHT组的平均CCT值大于其他各组,均P<0.01;NTG组的平均CCT值小于其他各组,均P<0.01。正常组CCT与眼压值呈正相关(r=0.318,R2=0.101,P<0.01)。OCT测量CCT的测量者间和测量者内的ICC值分别为0.995和0.996。结论OCT可以准确地测量CCT;NTG患者平均CCT比正常人薄,而OHT患者比正常人厚;CCT可以影响Goldmann压平眼压计的测量值,但贡献率较小。(中华眼科杂志,2006,42:199-203)     

Central corneal thickness and vascular risk factors in normal tension glaucoma

BACKGROUND: Normal tension glaucoma (NTG) has been shown to be associated with reduced central corneal thickness (CCT). The association of NTG with vascular risk factors is well documented. It has been postulated that a subset of NTG patients are misclassified due to incorrect intraocular pressure measurements on thin corneas. The aim of this study was to establish whether corneal thickness in NTG differs between patients with vascular risk factors specific to NTG and those without. METHODS: The study comprised a retrospective analysis of 108 eyes of 54 patients with NTG and 54 patients with primary open-angle glaucoma (POAG). Corneal thickness was measured in all patients. Vascular risk factors were recorded. Patients with NTG were divided into two groups depending on the presence (group A) or absence (group B) of vascular risk factors. RESULTS: The mean CCT was 549 +/- 34 microm in patients with POAG and 528 +/- 31 microm in patients with NTG (p = 0.001). Mean CCT was 512 +/- 31 microm in group A (n = 13) and 533 +/- 31 microm in group B (n = 41) (p = 0.034). A total of 40.9% of those with thin corneas (n = 22) had vascular risk factors versus only 12.5% of those with CCT within the normal range (n = 32) (p < 0.05). CONCLUSION: Central corneal thickness in NTG was significantly lower than in POAG and corneas were thinner in NTG patients with vascular risk factors than in those without. Vascular risk factors were significantly more common in patients with thin corneas. The finding of reduced corneal thickness in NTG does not obviate the need to consider vascular risk factors in the pathophysiology of the disease.     

Factors influencing central corneal thickness in a Turkish population

PURPOSE: The aim of this study is to find out the central corneal thickness (CCT) values for a Turkish patient group and to investigate the possible influences of age, sex, IOP, refractive status, keratometry readings, systemic disorders (hypertension, diabetes mellitus, hyperlipidemia, heart disease and asthma) on CCT values. MATERIALS AND METHODS: Six hundred twenty five subjects (276 male (44%), 349 female (56%)) of ages 6 to 88 years were recruited. Subjects who had corneal diseases, purulent conjunctivitis or blepharitis were excluded. Refraction and keratometry readings were made by MRK-3100 premium auto-ref/keratometer, IOP was measured by Reichert AT-555 auto noncontact pneumotonometer. RESULTS: Mean age was 44.1 +/- 16.6 years +/- SD for male subjects, 41.0 +/- 16.9 for females. Mean CCT +/- SD values for male was 552.2 +/- 35.9 microm, for female was 552.3 +/- 35.4 microm, respectively. There was no significant difference between right and left eye CCT values for both genders. Age and CCT was not correlated for the whole study group but there was a slight negative correlation in male subjects. IOP and CCT had moderately significant correlation for males and females. There was a slight significant correlation between Kh-Kv and CCT values for the whole group. In a multivariate regression model only Kv values seemed to affect CCT values. DISCUSSION: There are studies showing the variation of CCT values among different nations and ethnicities. There is no agreement about the relationship between age, IOP, Kh-Kv, spherical equivalence of refractive error, systemic disorders, menopause and CCT. In our study CCT was correlated with Kh-Kv and IOP in correlation analysis but in multivariate regression analysis only Kv appeared to influence corneal thickness.     

Central corneal thickness measurements in patients with normal tension glaucoma, primary open angle glaucoma, pseudoexfoliation glaucoma, or ocular hypertension.

BACKGROUND/AIMS: Recent studies have revealed patients with ocular hypertension to have thicker than normal central corneas and those with normal tension glaucoma to have thinner than normal ones, as determined by ultrasonic pachymetry. Since corneal thickness measurements and applanation tonometric estimates of intraocular pressure (IOP) correlate positively, monitoring of the former parameter have served as the basis for adjusting readings pertaining to the latter, with the consequence that many patients have had to be reclassified. With a view to validating these pachymetric studies, the central corneal thickness was determined in patients with normal tension glaucoma, primary open angle glaucoma, pseudoexfoliation glaucoma, or ocular hypertension, as well as that of normal subjects, using optical low coherence reflectometry, which is a new and more precise method than ultrasonic pachymetry. METHODS: 34 patients with normal tension glaucoma, 20 with primary open angle glaucoma, 13 with pseudoexfoliation glaucoma, and 12 with ocular hypertension, together with 21 control subjects, were included in this observational, concurrent case-control study. One eye per individual was randomly selected for investigation. IOP was measured by Goldmann applanation tonometry and central corneal thickness by optical low coherence reflectometry. RESULTS: Central corneal thickness was significantly higher (p < or =0.001) in patients with ocular hypertension than in normal individuals or in subjects with either normal tension glaucoma, primary open angle glaucoma, or pseudoexfoliation glaucoma, there being no significant differences between the latter four groups. Patients with ocular hypertension were also significantly younger (p < or =0.003) than those within any of the three glaucomatous groups. CONCLUSION: This study confirms that a significant number of patients with ocular hypertension have normal IOPs after the appropriate adjustments have been made for deviations from normal in their central corneal thickness. The accurate measurement of this latter parameter is important not only for individual patient care, in permitting more precise estimations of IOP, but also for clinical studies, in assuring a more reliable classification of subjects.     

Comparison of human central cornea and limbus in vivo using optical coherence tomography.

PURPOSE: The purpose of this study was to compare central corneal and limbal total and epithelial thickness using a commercially available optical coherence tomographer. METHODS: A Humphrey-Zeiss Optical Coherence Tomographer (OCT [Carl Zeiss, Meditec, Dublin, CA]) was used to obtain corneal images from 10 subjects. Central corneal and limbal total and epithelial thickness of both eyes were measured using the OCT. Each OCT image comprised 100 measurements, 10 nasal, 10 central, and 10 temporal measurements from each image were analysed. RESULTS: The central corneal and epithelial thickness of the right and the left eyes were 507.9 +/- 35.8 microm, 58.4 +/- 2.5 microm, 506.9 +/- 37.4 microm, and 58.5 +/- 2.5 microm, respectively. There were no differences between eyes (p > 0.05). The nasal and temporal limbal total and epithelial thickness of the right and left eyes were 703.8 +/- 32.1 microm, 704.9 +/- 31.0 microm, 76.8 +/- 3.5 microm, 77.9 +/- 2.9 microm, 704.4 +/- 31.8 microm, 706.3 +/- 32.5 microm, 77.5 +/- 2.8 microm, and 77.8 +/- 2.5 microm, respectively. There were no differences between the nasal and temporal total and epithelial thickness of both eyes (p > 0.05). However, there was a statistical difference between the central corneal and limbal total and epithelial thickness (both p < 0.05). CONCLUSIONS: Central cornea and limbus are measurably different using OCT. Central cornea is thinner than limbus for both total thickness and epithelial thickness. There is no difference between eyes of central corneal and limbal total and epithelial thickness. Optical Coherence Tomography is a useful instrument for in vivo human limbal morphometry.