Canadian perspectives in glaucoma management: the role of central corneal thickness

BACKGROUND: To propose consensus working recommendations for the role of central corneal thickness in the management of open-angle glaucoma. METHODS: This work is based on evidence from a review of the glaucoma literature, a Canadian consensus development workshop, and the personal clinical experience of the participating Canadian ophthalmologists. RESULTS: Guidelines were developed to provide eye care practitioners and their patients with support in the decision-making process for management of glaucoma or those at risk for developing glaucoma. INTERPRETATION: Further studies will be helpful in understanding the role of central corneal thickness in glaucoma management, and these guidelines will need to be revised periodically as new information becomes available.     

Normal-tension glaucoma and central corneal thickness.

PURPOSE: To determine whether a decreased corneal thickness is a primary factor in the lower intraocular pressure readings found in normal-tension glaucoma patients. METHODS: Fourteen patients with normal-tension glaucoma were compared with 14 age- and sex-matched glaucoma patients. Corneal thickness was measured by ultrasonic pachymetry on each eye. RESULTS: The corneal thickness (mean +/- SD) in patients with normal-tension glaucoma was 0.536 +/- 0.035 mm. The corneal thickness in patients with glaucoma was 0.537 +/- 0.035 mm. The 95% confidence interval for the difference between the two groups was -0.027 to +0.027 mm. CONCLUSION: It has been documented that increased corneal thickness leads to high readings of intraocular pressure. Therefore, decreased corneal thickness may lead to a lower intraocular pressure reading. This study suggests that for most normal-tension glaucoma patients corneal thickness is not a major factor in accounting for the lower intraocular pressure measurements when compared with primary open angle glaucoma patients.     

Evolution of central corneal thickness in children with congenital glaucoma requiring glaucoma surgery

Background The purpose of the study was to investigate the evolution of central corneal thickness (CCT) in correlation to the intraocular pressure (IOP) in children with congenital glaucoma before and after glaucoma surgery. Methods Nine eyes of five children (age 2 weeks to 6 months, mean 23 weeks) underwent trabeculotomy for congenital glaucoma. Corneal ultrasound pachymetry (PacScan 3000 AP, Technomed, Germany), tonometry using the Perkins tonometer, and slit-lamp examination (additionally to a clinical routine examination with retinoscopy, funduscopy, measurement of axial length and corneal diameter) were performed before and for at least 12 months after glaucoma surgery. In all children, corneal pachymetry and slit-lamp biomicroscopy—and whenever possible applanation tonometry—were performed without sedation or general anesthesia. If measurement of the IOP was not possible otherwise (in four of the five children), sedation with midazolam orally was used to measure the IOP at 2 weeks, 6 weeks, and 3 months after trabeculotomy, then every 3 months. Results Six of nine eyes had biomicroscopically clear corneas without visible corneal edema before trabeculotomy. In three eyes, a corneal edema was visible in at least one quadrant of the cornea. Regarding all eyes together, mean CCT was 651 ± 138 μm before trabeculotomy; this decreased to 592 ± 119 μm within 2 weeks after trabeculotomy. At 6 weeks and 3 months there was a further regression to 569.4 ± 16 μm. Mean IOP was 18.6 ± 7.5 mmHg before and decreased to 14.8 ± 5.8 mmHg after glaucoma surgery. Regarding IOP data obtained under general anaesthesia, decrease of CCT was significantly correlated with decrease in IOP. There was no significant difference in the correlation between eyes with and without visible corneal edema. Conclusions Corneal ultrasound pachymetry appears to be a valuable additional measure in the follow-up of infants and small children requiring glaucoma surgery. Financial interest: None Oral presentation at the annual meeting of the DOG (German Ophthalmological Society), Berlin, September 2006     

Long-term change in central corneal thickness from a glaucoma perspective

Aim:

To investigate the longitudinal change in central corneal thickness (CCT) over 3 years in patients with glaucoma.

Materials and Methods:

The Chennai Glaucoma Follow-up Study, an offshoot of the Chennai Glaucoma Study, was designed to evaluate the progression of glaucoma. A cohort of participants in the Chennai Glaucoma Study that were suffering from glaucoma or were at a higher risk for glaucoma underwent comprehensive ophthalmic evaluation at the base hospital at 6-month intervals during the years 2004 to 2007. The CCT (average of 10 readings) was measured between 11 am and 1 pm on any given day using an ultrasonic pachymeter. Patients with a history of ocular surgery, corneal disease and usage of topical carbonic anhydrase inhibitor were excluded. No patient was a contact lens wearer.

Results:

One hundred and ninety-six patients (84 male, 112 female) met the inclusion criteria. We analyzed data from the right eye. The mean age of the patients was 59.97 ± 9.06 years. Fifty-nine (30.1%) of the patients were diabetic. The mean change in CCT (CCT at first patient visit – CCT at last patient visit) was 3.46 ± 7.63 μm. The mean change in CCT was 0.75 μm per year (R² = 0.00). Age, gender, intraocular pressure at the first patient visit and diabetic status had no significant influence on the magnitude of change in CCT.

Conclusion:

A carefully obtained CCT reading by a trained examiner need not be repeated for at least 3 years as long as the ocular and systemic factors known to affect the measurement of CCT are constant.     

测量中央角膜厚度在青光眼诊治中的意义

眼压测量值是诊治青光眼的基本数据.近年来的研究结果 表明Goldmann压平眼压计等多种眼压计的测量值与中央角膜厚度(CCT)相关.由于人群中CCT个体差异明显,因此测量CCT对于了解患者实际眼压水平具有重要意义.此外,最新研究结果 显示薄角膜是高眼压症发展成为原发性开角型青光眼的独立危险因素,但薄角膜是否为发生青光眼性损伤的危险因素之一尚在争论中.有学者认为CCT的测量应当成为诊治青光眼的常规检查方法 之一.(中华眼科杂志,2009,45:184-188)     

The risk of glaucoma and corneal thickness

Intraocular pressure is still the most important risk factor for the development of glaucomatous optic nerve damage. There is growing evidence that corneal thickness is a risk factor for the development of glaucoma. This might be caused by the effect of corneal thickness on intraocular pressure (IOP) measurements. Goldmann applanation tonometry measurements are correlated with corneal thickness. Thick corneas lead to false high readings whereas thin corneas lead to false low readings. If corneal thickness as a risk factor for glaucoma is only related to the dependency of IOP measurements on corneal thickness or is related to possible different biomechanical tissue properties in glaucomatous eyes is not known. However, a large proportion of the corneal thickness effect seems to be related to the effect on IOP readings by applanation tonometry. Neglecting corneal thickness can lead to false measurements of IOP with consequent misdiagnosis and false treatment. Therefore, measurements of corneal thickness should be performed in glaucoma patients and suspects.     

Relationship between central corneal thickness and visual field defect in open-angle glaucoma

Purpose  

To explore the relationship between central corneal thickness (CCT) and visual field defect in open-angle glaucoma (OAG).     

Relationship between central corneal thickness and hypotony-related complications after glaucoma surgery

BACKGROUND AND OBJECTIVE: To examine the hypothesis that patients with increased central corneal thickness may have an overestimation of Goldmann applanation tension and a predisposition to hypotony-related complications. PATIENTS AND METHODS: A case-control analysis of patients with an intraocular pressure of 7 mm Hg or less on two consecutive postoperative visits following glaucoma filtration or drainage implant surgery was performed. Forward stepwise multiple logistic regression was used to determine the model that best predicted hypotony-related complications defined as choroidal effusion or hypotony maculopathy. RESULTS: Forty-three eyes (17 with hypotony-related complications and 26 controls) of 43 patients were enrolled. Eyes with pseudophakia (P = .006) and lower postoperative intraocular pressure (P = .013) were significantly more likely to develop hypotony-related complications. Mean central corneal thickness was similar in eyes with hypotony-related complications (519 +/- 32 microm) and controls (525 +/- 37 microm) and was not a significant predictor of hypotony-related complications in the multivariate model (P = .90). CONCLUSION: Increased central corneal thickness does not represent a risk factor for hypotony-related complications following glaucoma surgery.     

Combining corneal hysteresis with central corneal thickness and intraocular pressure for glaucoma risk assessment

Purpose

To determine whether adjusting corneal hysteresis (CH) values for central corneal thickness (CCT) and intraocular pressure (IOP) improves its capability to differentiate primary open-angle glaucoma (POAG) from ocular hypertension (OH).

Methods

This prospective, observational, cross-sectional study included 169 eyes of 169 subjects with a diagnosis of POAG (n=81) or OH (n=88). We utilized the Ocular Response Analyzer (ORA), Pascal Dynamic Contour Tonometer (DCT), Goldmann applanation tonometer (GAT), and ORA ultrasound pachymeter to obtain CH, IOP, and CCT values. Correlational, regression, and t-test analyses were conducted before and after the sample was divided into low, intermediate, and thick CCT subgroups.

Results

In the full sample, CH and CCT were moderately correlated (r=0.44, P<0.001). Although both were related to diagnosis in univariate regression analysis, only CH was independently related to glaucoma diagnosis in multivariate analysis. After the sample was divided into CCT tertiles, CH was significantly lower in POAG vs OH eyes within all three CCT subgroups, and CH was the only multivariate variable that differentiated POAG from OH in each CCT subgroup. Moreover, the relationship between CH and diagnosis was more robust within the CCT subgroups compared with the full sample, suggesting that integrating CCT into CH interpretation is beneficial. Adjusting CH for IOP did not aid diagnostic precision in this study.

Conclusion

Our findings suggest that combining CH and CCT for glaucoma risk assessment improves diagnostic capability compared to using either factor alone. Conversely, adjusting CH for IOP provided no clear clinical benefit in this study.     

近视眼中央角膜厚度和最薄角膜厚度的关系

目的 研究近视患者中央角膜厚度和最薄角膜厚度的大小、位置关系,以及近视程度对角膜厚度的影响.方法 回顾性病例对照研究.以接受近视性屈光手术的150例(300眼)为研究对象,根据等效球镜分为低、中、高近视3组,提取他们的术前Pentacam检查资料.左右眼参数的相关性和差异分别采用Pearson相关分析和配对t检验,多组比较采用方差分析,同一侧眼不同参数差异采用独立样本t检验.结果 左眼平均中央角膜厚度和最薄角膜厚度分别为(555.83±31.83)μm和(552.88±31.48)μm,右眼平均中央角膜厚度和最薄角膜厚度分别为(554.10±31.47) μm和(549.26±31.25)μm.左眼角膜最薄点72.00％(108/150)位于颞下方;右眼角膜最薄点70.67％(106/150)位于颞下方.不同程度近视组间的角膜厚度差异无统计学意义.结论 最薄角膜厚度与中央角膜厚度并不一致,双眼角膜最薄点均主要位于颞下方,其次在鼻下方.角膜厚度与近视程度无关.     

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.     

角膜厚度与青光眼危险性的关系

眼压是青光眼主要的致病因素与诊断指标之一，眼压测量值受中央角膜厚度的影响。中央角膜厚度个体差异较大，导致眼压测量值变异较大。中央角膜厚度与原发性开角型青光眼、正常眼压性青光眼及高眼压症患者的眼压之间存在一定的量化关系。角膜越厚，眼压测量值越高。对于正常角膜厚度青光眼患者，眼压受中央角膜厚度的影响不大。高眼压症患者、正常眼压性青光眼患者应常规作角膜厚度测量以排除角膜厚度的影响。中央角膜厚度，眼压与青光眼之间的关系有待于进一步研究。     

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.     

Synergic effect of corneal hysteresis and central corneal thickness in the risk of early-stage primary open-angle glaucoma progression

Graefe's Archive for Clinical and Experimental Ophthalmology - To evaluate corneal hysteresis (CH), acquired with ocular response analyzer (ORA), as a risk factor for glaucoma progression in...     

Circadian variations in central corneal thickness and intraocular pressure in patients with glaucoma

AIM: To analyse 24 hour variations in intraocular pressure (IOP) and central corneal thickness (CCT) in a group of glaucomatous patients. METHODS: 30 patients with primary open angle glaucoma were hospitalised and underwent circadian evaluations (at 8 pm, midnight, 4 am, 8 am, noon, and 4 pm) of supine and sitting IOP, respectively, measured using a Perkins and a Goldmann tonometer, and CCT measured using an ultrasonic pachymeter (the mean value of three measurements within 5 mum). All patients were treated with timolol 0.5% twice daily and latanoprost 0.005% once daily. RESULTS: Mean supine IOP was 15.3 (SD 3.7) mm Hg (range 10-25), with circadian fluctuations of 7.3 (3.3) mm Hg. Mean sitting IOP was 15.1 (3.9) mm Hg (range 8-26), with circadian fluctuations of 5.4 (3.1) mm Hg. Mean CCT was 534 (39) microm (range 443-637 microm) with circadian fluctuations of 16.5 (6.2) microm (range 6-31 microm). Both the within patient and within time point fluctuations in CCT were statistically significant (p<0.0001, ANOVA). CONCLUSIONS: The authors found considerable fluctuations in 24 hour IOP. The circadian fluctuations in CCT were small and, although statistically significant, did not seem to interfere with the circadian IOP assessment.     

Relationship between travoprost and central corneal thickness in ocular hypertension and open-angle glaucoma

PURPOSE: To evaluate whether treatment with travoprost, an F2a prostaglandin analog, affects central corneal thickness (CCT) and whether intraocular pressure (IOP) response to the medication is related to baseline CCT. METHODS: This was a prospective, interventional, nonrandomized, nonconsecutive, clinical trial. In this multicenter study, 379 total patients, 220 with newly or previously diagnosed open-angle glaucoma (OAG), 141 with ocular hypertension (OHT), and 18 unspecified, were recruited from 15 Canadian sites. IOP and CCT assessments were performed at baseline and 6 weeks after treatment with travoprost. Patients on IOP-lowering therapy at the time of enrollment were washed out for 4 weeks before baseline examinations. IOP was measured with Goldmann tonometers and CCT with Accutome IV pachymeters. Statistical analysis was performed with S-PLUS software. RESULTS: Posttherapy mean IOP decreased by 6.31 mm Hg or 24.4% (P < 0.001), and regression analysis indicated relatively greater IOP reduction in patients with higher pretherapy IOP (slope = 0.64; 95% CI, 0.54-0.76). Mean CCT decreased by 6.9 microm (P < 0.001). IOP reduction was not related to CCT reduction (slope = 0.253; 95% CI, -0.232 to 0.739; P = 0.305). Percent IOP decrease was not related to baseline CCT (slope = -0.02; 95% CI, -0.06 to 00.02; P = 0.33) in the total study sample. When OHT and OAG groups were considered separately, the OAG patients had less percent IOP decrease with thicker baseline CCT (slope = -0.067; 95% CI, -0.13 to -0.004; P = 0.037). CONCLUSIONS: Treatment with travoprost decreased IOP significantly and was associated with CCT thinning, which had little or no effect on actual IOP decrease. In the OAG group, IOP decrease was found to be statistically smaller in patients with thicker corneas.     

原发性青光眼及高眼压症患者中央角膜厚度的比较研究

目的 探讨用超声角膜测厚仪测量的急性原发性闭角型青光眼、慢性原发性闭角型青光眼、原发性开角型青光眼、高眼压症及正常人中央角膜厚度(central corneal thickness,CCT)的差异.方法 临床病例对照研究.对2010年2月至2011年11月在承德医学院附属医院眼科应用超声角膜测厚仪测量62例(107只眼)的CCT值.急性原发性闭角型青光眼16例(18只眼)、慢性原发性闭角型青光眼14例(26只眼)、原发性开角型青光眼10例(19只眼)、高眼压症6例(12只眼)及正常人16例(32只眼).采用单因素方差分析及SNK-q检验行统计分析.结果 各组CCT值:急性原发性闭角型青光眼(548.44±30.46)μm、慢性原发性闭角型青光眼(522.70±50.39)μm、原发性开角型青光眼(546.32±22.85) μm、高眼压症(585.67±21.22) μm、正常人(536.38±26.53)μm.组间比较差异有统计学意义(F=7.661,P＜0.01).两两比较显示:高眼压症与原发性青光眼组及正常人比较,差异有统计学意义;原发性青光眼各组及正常人两两比较,差异无统计学意义.结论 与正常人及原发性青光眼相比,高眼压症CCT较厚;原发性青光眼CCT与正常人相比差异无统计学意义;CCT与原发性青光眼类型无相关性.