Relationship between corneal thickness and measured intraocular pressure in a general ophthalmology clinic

OBJECTIVE: To assess whether central corneal thickness (CCT) is a confounding factor in the classification of patients attending for glaucoma assessment in a district general hospital. DESIGN: Cross-sectional study by a single observer. PARTICIPANTS: Patients attending a general ophthalmic clinic: 235 clinically normal eyes, 52 eyes with normal-tension glaucoma (NTG), 335 eyes with primary open-angle glaucoma (POAG), 12 eyes with pseudoexfoliative glaucoma (PXE), 42 eyes with chronic angle closure glaucoma (CACG), and 232 glaucoma suspect (GS) eyes. INTERVENTION: Central corneal thickness was measured using ultrasonic pachymetry. MAIN OUTCOME MEASURE: Correlation of CCT and diagnosis. RESULTS: Mean CCT was 553.9 microm (95% confidence intervals [CI] for the mean, 549.0-558.8 microm) in the clinically normal eyes, 550.1 microm (95% CI, 546.6-553.7 microm) in the POAG eyes, 514.0 microm (95% CI, 504.8-523.3 microm) in the NTG eyes, 530.7 microm (95% CI, 511.2-550.1 microm) in the PXE eyes, 559.9 microm (95% CI, 546.8-573.0 microm) in the CACG eyes, and 579.5 microm (95% CI, 574.8-584.1 microm) in the GS eyes. The differences of mean CCT between the groups were highly significant (P< 0.001 analysis of variance). Eighty-five percent of eyes with NTG and only 36% of eyes with POAG had a mean CCT of 540 microm or less. Thirteen percent of eyes with POAG and 42% of GS eyes had a mean CCT greater than 585 microm. CONCLUSIONS: The CCT measurement is desirable in patients attending for glaucoma assessment in a district general hospital to avoid misclassification resulting from the relationship between CCT and tonometric pressure. Central corneal thickness alone is not an accurate predictor for the clinical diagnosis in this group of eyes. However, many eyes diagnosed as having NTG have thin corneas, which would tend to lower the tonometrically recorded intraocular pressure (IOP), so the finding of a less-than-normal thickness cornea introduces some doubt as to the diagnosis of NTG. For the GS eyes, most eyes had thick corneas, which would tend to increase the tonometrically recorded IOP. Thus, GS eyes with modest elevation of IOP and a thick cornea may be at low risk of progressing to POAG. Thus, many patients with "high IOPs" and a thick CCT do not necessarily have high IOPs and may not need to be followed as GS eyes.     

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)     

Comparison of central and peripheral corneal thicknesses between normal subjects and patients with primary open angle glaucoma, normal tension glaucoma and pseudoexfoliation glaucoma

BACKGROUND: While many comparative data are available about central corneal thickness in different types of open angle glaucoma, peripheral corneal thickness has been much less investigated up to now. Thus, the aim of this study was to compare the central and peripheral corneal thicknesses in patients with primary open angle glaucoma (POAG), normal tension glaucoma (NTG) and pseudoexfoliation glaucoma (PEXG) to values of normal subjects. PATIENTS: 104 patients with POAG, 20 patients with NTG, 23 patients with PEXG and 127 normal subjects were investigated with the Orbscan II. The central corneal thickness and the peripheral corneal thickness at 3 mm distance from the centre were determined in 4 quadrants. The acoustic equivalent factor of 0.92 was not used. Patients with eye diseases, patients who had undergone eye surgery or wearers of contact lenses were excluded. Differences were analysed with the Bonferroni-adjusted Mann-Whitney U Test for statistical significance. RESULTS: The median central corneal thickness in POAG was 600 +/- 35 microm, in NTG 577 +/- 31 microm, in PEXG 603 +/- 25 microm and in the control group 606 +/- 38 microm. The difference between NTG and the control group was statistically significant (p = 0.01). Superiorly the peripheral corneal thickness was lower in POAG (670 +/- 47 microm) and NTG (639 +/- 37 microm) compared to the control group (686 +/- 46 microm). Nasally the peripheral corneal thickness was lower in POAG (656 +/- 48 microm), NTG (658 +/- 55 microm) and PEXG (642 +/- 47 microm) compared to the control group (677 +/- 46 microm). Temporally and inferiorly there were only small differences compared to the control group. The differences in peripheral corneal thickness were not statistically significant. DISCUSSION: In accord with literature data the central corneal thickness was lower in patients with normal tension glaucoma compared to normal subjects. Superiorly and nasally the peripheral corneal thickness was lower in patients with open angle glaucoma than in normal subjects which was, however, not statistically significant. To what extent these characteristics of the corneal architecture are relevant for the pathogenesis of open angle glaucomas has to be clarified in further larger trials.     

Comparison of central corneal thickness in patients participating in a glaucoma screening programme and those who were examined in the glaucoma unit

BACKGROUND: The aim of this study was to compare central corneal thickness (CCT) and intraocular pressure in patients participating in a glaucoma screening programme and patients who were examined in the glaucoma unit. MATERIALS AND METHODS: 406 patients of a glaucoma screening programme (Salzburg-Moorfields collaborative glaucoma study) were included in this study. In addition a group of 406 patients who were admitted to the glaucoma clinic for a detailed glaucoma examination was included (outpatient clinic group). In all participants central corneal thickness (CCT) was measured and possible relations of CCT within the study groups were statistically analysed. RESULTS: In the population screening group the mean central corneal thickness in normal subjects was 536+/-4.3 microm, in patients with ocular hypertension (OHT) 552+/-5.7 microm, patients suffering from a normal tension glaucoma (NTG) showed a mean CCT of 534+/-14.2 microm and those with primary open angle glaucoma (POAG) had a value of 521+/-17.9 microm. In the 'outpatient clinic group' the OHT subgroup had a mean CCT of 553+/-6.8 microm, the NTG subgroup of 529+/-26.5 microm and the one with POAG had a mean of 527+/-19.8 microm. In addition, CCT was measured in all glaucoma patients whose "partner" eye was healthy (544+/-5 microm) and included in this study as part of the normal subgroup. In both groups (screening group and outpatient group), CCT was significantly higher in OHT patients than in normals. In contrast, no statistically significant difference between normals and NTG or POAG patients was detected. Intraocular pressure was significantly lower in the screening groups than in the other ones. CONCLUSIONS: Our data confirm the previously published results concerning OHT and healthy subjects. In this study no significant difference between NTG or POAG subjects and normal eyes was detected. The lower IOP in the screening population can be explained by the fact that patients contacting the screening program are self selected whereas patients of the glaucoma unit are admitted by practising ophthalmologists and are, therefore, rather advanced cases or carrying special risk factors.     

Familial occurrence of artefactual ocular hypertension from thick corneas and of primary open angle glaucoma in a French Canadian kindred

We describe the coexistence of artefactual ocular hypertension due to increased central corneal thickness (CCT>585 microm), with primary open angle glaucoma (POAG) in a French Canadian kindred. Seventeen members of the family were examined and classified as to their glaucoma status. The mean CCT for our glaucoma patients (580 microm; n=5) and that for normals (552 microm; n=6) were within two standard deviations of the mean value provided in the literature (531 microm +/- SD=29 microm). The mean CCT of 611 microm for the suspect group (n=6) was considerably higher than for the glaucoma and normal groups. All but one of the suspects were classified as ocular hypertensives on the basis of high intraocular pressures (IOPs). When the IOPs for these patients (mean 22.6 mmHg) were corrected for their CCTs, all had pressures of <21 mmHg (mean 16.4 mmHg). Ten of the seventeen family members had thick CCTs, and transmission of thick corneas was seen in two generations. A number of individuals in this family had optic nerve head drusen (9/17) and the mean CCT of these individuals (601 microm) was higher than the mean CCT (560 microm) of the group without drusen (P=0.020 by t test). Artefactual ocular hypertension and POAG can be present in different members of the same family. The presence of a thick cornea appears to be an inherited trait and may be associated with the presence of optic nerve drusen. This association suggests a developmental relationship between thick corneas and optic nerve head drusen which needs to be studied further.     

角膜厚度与高眼压症及青光眼的眼压

目的 探讨高眼压症、正常眼压性青光眼、原发性开角型青光眼患者及正常人的角膜厚度差异,分析角膜厚度与眼压间的关系,以及角膜厚度的测定对各型青光眼的诊断意见。方法 用超声波角膜测厚仪检测７３例（７３只眼）高眼压症、７９例（７９只眼）正常人的中央角膜厚度,并将其测定结果进行比较。回顾性分析每只青光眼治疗前的最高眼压（Ｇｏｌｄｍａｎｎ）,包括２４ｈ眼压曲线,用Ｅｈｌｅｒ法通过中央角膜厚度对眼压进行校正。结     

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.     

Impact of prostaglandin-F(2alpha)-analogues and carbonic anhydrase inhibitors on central corneal thickness -- a cross-sectional study on 403 eyes

BACKGROUND: Histological changes of, in particular, collagen and extracellular matrix after administration of topical prostaglandin F(2alpha)(PGF (2alpha)) analogues have been reported. In view of this observation, we investigated the influence of PGF(2alpha) analogues on the central corneal thickness. PATIENTS AND METHODS: In a non-randomized, controlled, cross-sectional study, 403 eyes from 208 consecutive patients were examined: 149 eyes (normals/controls) and 79 with ocular hypertension (OHT), 119 eyes with primary open angle glaucoma (POAG) and 56 eyes with normal tension glaucoma (NTG). One experienced ophthalmologist measured the central corneal thickness (CCT) using ultrasound pachymetry (Tomey AL-2000, sequence of 5 measurements with an SD < 3 microm). The central corneal power was measured with the Zeiss keratometer. Depending on the topical treatment, the patients were classified into 4 groups: A) PGF(2alpha) analogues (n = 78), B) carbonic anhydrase inhibitors (n = 26), C) combination of PGF (2)(alpha) analogues and carbonic anhydrase inhibitors (n = 41), D) none of these drugs (n = 258). T tests and multiple linear regression analyses were used for statistical analysis. RESULTS: CCT was decreased significantly (p < 0.01 each) in eyes treated with PGF(2alpha) analogues (group A: 529 +/- 34 microM), in comparison with the untreated and non-glaucomatous eyes (part of group D: 542 +/- 35 microM, n = 148), untreated glaucomatous/OHT eyes (part of group D: 563 +/- 37 microM, n = 110), eyes treated with carbonic anhydrase inhibitors (group B: 561 +/- 32 microm) and eyes with a topical application of both PGF (2)(alpha) analogues and carbonic anhydrase inhibitors (group C: 555 +/- 48 microM. No correlation was found between CCT and diagnosis (OHT, POAG, NTG, control), gender, central corneal power, and intraocular pressure in a multivariate analysis. CONCLUSIONS: The present findings suggest that the topical application of prostaglandin F(2alpha) analogues onto the cornea reduces the central corneal thickness significantly. These changes might be attributed to effects of PGF(2alpha) analogues on the extracellular matrix of the corneal stroma via upregulation of matrix metalloproteinases. In clinical practice, corneal thinning under local PGF (2)(alpha) analogue treatment could result in underestimation of intraocular pressure levels as measured by applanation tonometry.     

Corneal thickness and visual field damage in glaucoma patients

PURPOSE: To verify whether there was a significant correlation between central corneal thickness (CCT) and visual field damage in patients with primary open angle glaucoma (POAG). METHODS: A total of 99 eyes with POAG were consecutively recruited. Patients were classified as glaucomatous based on visual field and optic nerve head damage. All underwent applanation tonometry, Humphrey perimetry, and measurement of CCT with ultrasonic pachymetry. Based on CCT value, the sample was split at the mode in two groups (group 1<535 microm, n=49; group 2>or=535 microm, n=50). RESULTS: Entire cohort: mean CCT 554 microm+/-45.03; mean deviation (MD) -6.68 dB+/-7.32; pattern standard deviation (PSD) 5.33+/-3.75; intraocular pressure (IOP) 17.91+/-4.16 mmHg with treatment. Group 1: CCT was 504.8 microm+/-30.8; MD -9.01 dB+/-8.72; PSD 6.38+/-3.99; IOP 18.02 mmHg+/-4.66. Group 2: mean CCT 574.6 microm+/-35.03; MD -4.39 dB+/-4.70; PSD 4.25+/-3.19; IOP 17.79 mmHg+/-3.57. A significant difference was found between the two groups for both MD and PSD. Linear regression analysis showed a significant correlation between CCT and PSD (P<0.001). CONCLUSIONS: Our data show that patients with a thinner cornea had a worse MD and PSD. As a thinner CCT causes an underestimation of the true IOP, there may be a delay in the diagnosis of POAG or an inadequate estimate of the clinical course despite apparently desirable IOP applanation readings.     

Central corneal thickness and correlation to optic disc size: a potential link for susceptibility to glaucoma

AIMS: To evaluate a possible relationship between central corneal thickness (CCT) and optic disc area in patients with primary open-angle glaucoma (POAG). METHODS: Patients with POAG underwent eye examination, optic disc imaging with the Heidelberg Retina Tomograph II (HRT II) and ultrasound corneal pachymetry. Exclusion criteria were prior ocular surgery and low-quality HRT II images (HRT standard deviation (SD) >50). Pearson's correlation coefficients were calculated to assess the associations between CCT and optic disc area. RESULTS: 212 eyes of 137 patients with POAG were examined. In all, 66 (48%) subjects were women, 104 (76%) were Caucasian, 26 (19%) African-American and 7 (5%) other races. 72 eyes remained after excluding those with prior intraocular surgery and low-quality HRT II images. In a univariate analysis of this group, CCT was inversely correlated with optic disc surface area (Pearson's correlation coefficient r = -0.284, p = 0.036, n = 72). Mean (SD) disc area was 2 (0.53) mm(2) (n = 160). Caucasians had significantly smaller discs (p<0.001) than other races (Caucasian 1.9 (0.47) mm(2) (n = 119), African-Americans 2.4 (0.54) mm(2) (n = 31), other races 2.3 (0.45) mm(2) (n = 10)). CONCLUSION: CCT is inversely correlated to optic disc area. Although thicker corneas have been recognised to cause slight overestimation of true intraocular pressure (IOP), they may also indicate the presence of a substantially smaller, and thus more robust, optic nerve head. People with thinner corneas which slightly underestimate the true IOP may also have larger and more deformable optic discs.     

Comparison of dynamic contour tonometry with goldman applanation tonometry over a wide range of central corneal thickness

PURPOSE: To compare dynamic contour tonometry with Goldmann applanation tonometry in structurally normal corneas over a wide range of central corneal thickness (CCT). PATIENTS AND METHODS: Twenty-five patients each with normal CCT (group A), thin corneas (group B), and thick corneas (group C) had IOP measured with the Goldmann (GAT) and dynamic contour tonometer (DCT). RESULTS: In group A (mean CCT = 552 +/- 16 microm) the mean GAT was 15.9 +/- 3.1 mm Hg and mean DCT was 16 +/- 3.3 mm Hg (P = 0.91). In group B (mean CCT = 491 +/- 19 microm) the mean GAT was 13.2 +/- 3.5 mm Hg and the mean DCT was 15.9 +/- 3.5 mm Hg (P = 0.009). For group C (mean CCT = 615 +/- 22 microm), the mean GAT was 17.4 +/- 3.8 mm Hg and the mean DCT was 17.4 +/- 3.5 mm Hg (P = 0.95). The 95% agreement limits for DCT were -3.1 mm Hg to 2.9 mm Hg. The mean GAT-DCT difference was -2.6 mm Hg in thin corneas and -0.06 mm Hg in thick corneas. Below 520 microm reduction of 10 microm in CCT appears to result in a significant underestimation of the GAT IOP by 0.7 mm Hg (P < .001) and above 580 microm a non-significant overestimation of 0.2 mm Hg per 10 microm increase in CCT (P = 0.27). CONCLUSION: Dynamic contour tonometer agrees well on average with GAT but the agreement limits are wide. In structurally normal thin corneas DCT may give a more accurate assessment of the true IOP but it does not appear to have any benefit over GAT in thick corneas.     

Role of central corneal thickness on baseline parameters and progression of visual fields in open angle glaucoma

PURPOSE: To evaluate the relationship of central corneal thickness (CCT) to baseline visual field parameters and visual field progression in patients with primary open-angle glaucoma (POAG). METHODS: Charts of consecutive patients with POAG were reviewed to obtain visual field data. Visual field was measured by standard threshold static perimetry. Variables analyzed included mean deviation (MD) and pattern standard deviation (PSD). RESULTS: A total of 121 eyes examined over 4 years were evaluated. A significant negative relationship between CCT and PSD (correlation coefficient: -0.02, p<0.05) was found. Analyses comparing CCT to change in PSD and MD (visual field progression) were statistically not significant. CONCLUSIONS: Patients with thinner corneas initially present with a greater visual field defect, indicating that thin corneas may contribute to advanced glaucomatous damage at the time of diagnosis. However, CCT does not seem to be a significant risk factor for progression of the disease.     

Central corneal thickness measurement in clinical practice

OBJECTIVE: To determine if a single measurement of central corneal thickness (CCT) is an adequate sample to aid in glaucoma risk assessment in clinical practice. METHODS: Central corneal thickness was measured by ultrasound pachymetry (mean of 15 measurements for each eye) on two separate occasions at least one month apart (range, 33 to 610 days). Eyes with a history of prior incisional surgery or corneal pathology were excluded. RESULTS: Ninety-eight eyes of 98 patients (43 male, 55 female) were enrolled. Mean age was 61.2 +/- 15.5 years. Mean inter-test period was 276 +/- 124 days. No significant difference in mean CCT was observed between the two visits (549 +/- 41 microm versus 548 +/- 42 microm, P = 0.4, two-tailed, paired t test). Measured CCT values differed by more than 20 microm in 20 eyes (20.4%), whereas CCT difference of at least 40 microm was seen in 5 eyes (5.1%). There was no correlation between the measured or absolute difference in CCT and IOP (r = -0.016, P > 0.43), inter-test time period (r = 0.072, P > 0.23), and glaucoma diagnosis. CONCLUSION: Central corneal thickness measurements in this study differed by at least 20 microm in 20% of eyes. This has important implications for risk assessment, management, and follow-up of patients with glaucoma and related disorders. Factors affecting CCT measurement, such as examiner error or true alterations in corneal thickness, require continued investigation.     

The relationship between central corneal thickness-adjusted intraocular pressure and glaucomatous visual-field loss.

BACKGROUND: Although measurement of central corneal thickness (CCT) is increasingly becoming an important component of glaucoma risk analysis, significant controversy exists regarding the benefit of calculating a corrected intraocular pressure (IOP) value from measured IOP and CCT data. METHODS: Three hundred forty-four male subjects were identified from a VA eye clinic with one of the following clinical diagnoses: ocular hypertension (OHT), primary open-angle glaucoma (POAG), normal tension glaucoma (NTG), and normal tension glaucoma suspect (NTGS). Using one eye per subject, multivariate logistic regression and correlational analyses were performed to determine relationships between glaucomatous visual-field loss and several glaucoma risk factors, including adjusted IOP values. RESULTS: Multivariate logistic regression analysis did not identify CCT-adjusted IOP values as independent risk factors for development of either NTG or POAG-related glaucomatous visual-field loss. CCT, however, was found to be strongly associated with both NTG and POAG-related visual-field loss. Correlational analysis revealed a weak correlation between Ehlers-adjusted pre-treatment IOP and severity of POAG-related visual-field loss, but no other adjusted IOP values significantly correlated with severity of visual-field loss in either POAG or NTG. CONCLUSIONS: Our results suggest that adjusted IOP, as calculated using current algorithms, is not useful within glaucoma risk analysis, since adjusted IOP was unable to predict either presence or severity of glaucomatous visual-field loss in this study. CCT, conversely, was found to be a robust and independent predictor of glaucomatous visual-field loss. These findings, while supporting routine CCT measurements for all glaucoma suspects, do not support routine clinical computation of adjusted IOP values using current algorithms.     

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.     

Correlation between retinal nerve fiber layer thickness and central corneal thickness in patients with ocular hypertension: an optical coherence tomography study

PURPOSE: To correlate the retinal nerve fiber layer (RNFL) thickness and optic nerve head (ONH) parameters measured by optical coherence tomography (OCT) with central corneal thickness (CCT) measurements in patients with ocular hypertension (OHT). DESIGN: Observational cross-sectional study. METHODS: setting: Tertiary care referral teaching institute. study population: Fifty-one eyes of 51 patients with OHT and 35 eyes of 35 normal subjects. Both groups were stratified into thin (CCT < or =555 microm) and thick (CCT >555 microm) cornea subsets. Ocular hypertensives were further stratified by CCT into < or =555 microm, 556 to 588 microm, and >588 microm subsets. observation procedure: RNFL thickness (average, superior average, and inferior average) and ONH parameters were measured by OCT. CCT was measured by ultrasonic pachymetry. main outcome measures: Correlation between CCT and OCT measurements of RNFL and ONH parameters. RESULTS: In the OHT group, CCT correlated significantly with all three RNFL measurements (Pearson's coefficient r = 0.412, 0.484, and 0.380, respectively) but with only four ONH parameters (cup-to-disk area ratio, cup area, rim area, and horizontally integrated rim width; r = -0.459, -0.283, 0.421, and 0.436, respectively). The RNFL in ocular hypertensives with CCT < or =555 microm was significantly thinner than in those with thick corneas (analysis of variance, post hoc Bonferroni comparisons, P < .001). RNFL thickness of normal subjects and ocular hypertensives with CCT >555 microm were similar. CONCLUSIONS: Ocular hypertensives with CCT < or =555 microm may represent patients who have either very early undetected glaucoma or an inherent structural predisposition to glaucomatous damage. This may in part explain the higher risk of these patients for progression to glaucoma.     

薄角膜正常眼压性青光眼OCT检测与分析

目的 探讨薄角膜正常眼压性青光眼(NTG)患者视盘周围视网膜神经纤维层(RNFL)厚度及视盘结构的OCT特征.方法 采用OCT对21例(42只眼)中央角膜厚度(CCT)低于正常人群范围(＜500μm)的正常眼压性青光眼患者进行RNFL及视盘扫描,并根据其CCT值分为:组1(480μm≤CCT＜500μm)和组2(460μm≤CCT＜480μm),比较分析两组RNFL厚度、视盘参数及30.中心视野指数.结果 两组患者的OCT检测参数包括Avg.Thick、Savg、Iavg、Navg、Tavg差异无统计学意义(P＞0.05),Max-Min值差异有统计学意义(P＜0.05);视盘参数(垂直盘沿容积值等)、视野参数(MD、MS值)差异无统计学意义(P＞0.05).两组患者的RNFL平均厚度与视野平均缺损值MD呈强且负的直线关系(r=-0.602,P=0.000).结论 OCT能对NTG患者视盘及视网膜神经纤维层做出定量测量和分析,且与视野检测指标有良好的相关性,在NTG的早期诊断中有重要意义;薄角膜NTG患者的角膜厚度水平与视网膜神经纤维层缺损程度无明显相关.

Abstract：

Objective To investigate the thickness changes of peripapillary retinal nerve fiber layer (RNFL) in normal tension glaucoma (NTG) with thin cornea measured by optical coherence tomography (OCT).Methods Twenty-one NTG patients (42 eyes) with thin cornea were divided into two groups according to their central corneal thickness (CCT):group 1 (480μm≤CCT＜500μm) and group 2 (460μm≤CCT＜480μm),and analysis the different results of OCT scan and visual outcome in two groups.Results There were no significant differences in OCT parameters of Avg.,Thick,Savg,Iavg,Navg and Tavg among the two groups (P ＞0.05),while Max-Min was lower in group 2 (P ＜0.05);There were also no significant differences in the optic nerve head analysis results,visual field mean defect (MD) and mean sensitivity (MS) among two groups (P＞0.05).The average RNFL thickness and MD showed a strong and negative linear relationship(r =-0.602,P =0.000).Conclusions OCT can make quantitative measurement and analysis of optic disc and RNFL for NTG patients,and has a good correlation with vision field.It has important significance in the early diagnosis of NTG.For NTG patients with thin corneas,there is no significant correlation between the level of CCT and extent of retinal nerve fiber layer defect.     

Corneal thickness in glaucoma: an important parameter?

Central corneal thickness was measured by pachometry in 49 patients with primary open-angle glaucoma (POAG), 41 with ocular hypertension (OHT), 14 with normal tension glaucoma (NTG) and 48 normal subjects. The mean corneal thickness of the OHT patients was significantly greater than that of the normal control group. The NTG patients, on the other hand, had a cornea on average thinner than the normals. These differences may cause misclassification of normals with a thick cornea as ocular hypertensive eyes or, contrarywise, cause those normals whose IOP is underestimated because of a thin cornea to be classed as NTG patients.     

Central corneal thickness and measured IOP: a clinical study.

PURPOSE: We have attempted to document that the pachometer used in primary eye care practices will show the same corneal thickness relationship with measured intraocular pressure (mIOP) as the research studies. A second purpose of the study is to determine what role, if any, corneal thickness has on the increase in mIOP with age. METHODS: Sonogage Corneo-Gage Plus ultrasound central corneal thickness (CCT) measurements were taken on 101 white ocular hypertensive (OHT) patients with mIOP at or above 21 mmHg, as measured by Goldmann tonometry, and compared with age-matched controls with mIOP of 16 mmHg or less. To evaluate the impact of CCT on mIOP with age, a subset of patients was selected from the subjects and controls who had had a Goldmann tonometry reading recorded more than 10 years before the collection of the study data. RESULTS: The mean age of the (OHT) patients was 65.3 years +/- 12.3. The average CCT of the OHT patients was 595 pm +/- 36 microm, and for the control patients the average CCT was 554 microm +/- 34 microm. This difference was statistically significant (P < 0.0001). Evaluation of the age subset revealed that patients with thick corneas showed a 1.22 mmHg increase in mIOP per decade, whereas the patients with thin corneas showed a 0.69 mmHg decrease in mIOP per decade. This difference was statistically significant (P = 0.0001). This study demonstrates the same relationship between corneal thickness and mIOP in clinical practice as has been reported from research settings. This finding suggests that knowledge of corneal thickness is necessary to adjust the mIOP to better monitor and evaluate patients for glaucoma risk in the primary eye care practice. Of more significance is the finding that mIOP increases in the thick cornea patients over time. This suggests an age-related change in corneal resistance to applanation that impacts on mIOP measurements. More study is needed pertaining to the role of CCT on mIOP.