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.     

Central corneal thickness and intraocular pressure measures in human corneas with endothelial guttata: an observational quality control study

Purpose: The aim of the present study was to assess central corneal thickness (CCT) and intraocular pressure (IOP) in eyes where the corneas were affected by different degrees of severity of endothelial pseudo‐guttata or guttata. Methods: In a prospective, case series observational study, non‐contact tonometry and non‐contact specular microscopy (NCSM) with pachymetry for central corneal thickness measures were undertaken as routine procedures on predominantly older patients without a history of corneal problems or contact lens wear. For those showing any signs of corneal endothelial abnormalities, images of the central cornea endothelium were further processed to measure the area (as a percentage) occupied by the guttata. Results: Abnormal endothelial images were obtained from 43 patients (seven with bilateral changes) with an average age of 67.5 years. Between 1.5 and 54.9 per cent of the endothelial images were affected by guttata, which were assigned grade 1 (20 eyes), grade 2 (18 eyes) or grade 3 (11 eyes). When assessed by grade, the central corneal thickness increased and the measured IOP decreased as the guttata became more numerous and confluent. Regression analyses revealed only a weak association between central corneal thickness (p = 0.044, r = 0.149) or the measured IOP (p = 0.090, r = ‐0.244) and the extent of the guttata (percentage). With the apparently contrasting IOP and central corneal thickness effects, no significant IOP‐CCT relationship was noted (p ≥ 0.268, r ≤ 0.160). Conclusions: Where corneas have mild‐to‐modest non‐dystrophic endothelial guttata, there may be a less predictable effect of corneal thickness on the outcome of tonometry.     

Association between corneal hysteresis and central corneal thickness in glaucomatous and non‐glaucomatous eyes

Purpose: We aimed to determine corneal hysteresis values (CH) using the ocular response analyser (ORA) in non‐glaucomatous and glaucomatous eyes and their relationship with central corneal thickness (CCT). Methods: Corneal hysteresis, intraocular pressure (IOP) as measured by Goldmann applanation tonometry (GAT) and CCT were prospectively evaluated in 74 non‐glaucoma subjects with IOP < 21 mmHg and in 108 patients with treated primary open‐angle glaucoma (POAG). One eye in each subject was randomly selected for inclusion in the analysis. Results: Mean (± standard deviation [SD]) age was 59.2 ± 14.2 years in the non‐glaucoma group and 62.4 ± 9.8 years in the glaucoma group. Mean (± SD) GAT IOP was 15.7 ± 2.65 mmHg and 16.38 ± 2.73 mmHg in the non‐glaucoma and glaucoma groups, respectively. There was no statistically significant difference between the two groups in mean age (p = 0.396) or mean GAT IOP (p = 0.098). Mean (± SD) CH was 10.97 ± 1.59 mmHg in the non‐glaucoma and 8.95 ± 1.27 mmHg in the glaucoma groups, respectively. The difference in mean CH between the two groups was statistically significant (p < 0.0001). There was a strong positive correlation between CH and CCT in the non‐glaucoma group (r = 0.743) and a significantly (p = 0.001) weaker correlation (r = 0.426) in the glaucoma group. Conclusions: Corneal hysteresis was significantly lower in eyes with treated POAG than in non‐glaucomatous eyes. The corneal biomechanical response was strongly associated with CCT in non‐glaucoma subjects, but only moderately so in glaucoma patients. It can be assumed that diverse structural factors, in addition to thickness, determine the differences in the corneal biomechanical profile between non‐glaucomatous and glaucomatous eyes. Corneal hysteresis could be a useful tool in the diagnosis of glaucoma.     

Intraocular pressure in an ophthalmologically normal Japanese population

Purpose: To investigate the distribution of intraocular pressure (IOP) measured by Goldmann applanation tonometry (GAT) and factors correlating with IOP, with special attention to age, in a large sample of ophthalmologically normal Japanese subjects. Methods: A total of 7313 subjects (2847 male, 4466 female) were selected as a normal Japanese sample. The following exclusion criteria applied: abnormal results suggestive of any eye diseases in slit‐lamp examination, fundus photography or visual field testing using frequency‐doubling technology; corrected visual acuity < 0.7, and contact lens wear within 1 week of study examinations. All subjects were sourced from the Eye Disease Screening Service in Tajimi City, which carried out a screening programme between September 2000 and October 2001. All data, including subject age, gender, body mass index (BMI), systolic blood pressure (BP), laterality, refraction, corneal radius and IOP measured with GAT were collected from subject records. Central corneal thickness (CCT) was measured by SP‐2000P specular microscopy. Levels of IOP and correlating factors were statistically analysed. Results: Average IOP was 14.1 ± 2.3 mmHg (mean ± standard deviation; n = 7313 × 2). Mean IOP levels in male and female subjects were 14.1 ± 2.3 mmHg and 14.1 ± 2.2 mmHg, respectively. There was no difference in IOP between male and female subjects. Multiple regression analysis indicated that IOP had negative correlations with age, corneal radius and refraction (p < 0.0001), and positive correlations with CCT, systolic BP and BMI (p < 0.0001). Conclusions: In a large‐scale population of ophthalmologically normal Japanese subjects, IOP measured by GAT was significantly and negatively correlated with age. It was also negatively correlated with corneal radius and refraction, and positively with CCT, systolic BP and BMI.     

Repeatability and accuracy of applanation resonance tonometry in healthy subjects and patients with glaucoma

Purpose: To evaluate the repeatability and accuracy of the applanation resonance tonometer (ART) used in the automatic servo‐controlled version, and to evaluate the influence of central corneal thickness (CCT) on the ART intraocular pressure (IOP) measurements. Methods: This prospective, randomized, single‐centre study included one eye of 153 subjects (35 healthy volunteers and 118 patients with glaucoma). All participants underwent ultrasonic CCT measurement, followed by IOP evaluation with Goldmann applanation tonometer (GAT) and ART in random order. A single operator measured the IOP with each tonometer three times. Intra‐examiner variability was evaluated using the coefficient of variation (CoV), intraclass correlation coefficient (ICC) and test–retest differences. Intermethod agreement was assessed using the Bland–Altman method. Linear regression analysis was used to evaluate the relationship between IOP measurements and CCT. Results: The mean IOP was 17.7 ± 4.4 mmHg with GAT and 20.6 ± 5.3 mmHg with ART (p < 0.001). CoV and ICC were, respectively, 5 ± 3% and 0.99 for GAT, and 8 ± 4% and 0.96 for ART (intermethods differences, p = 0.001). The ART test–retest differences significantly increased with increasing mean IOP (p = 0.003). The mean IOP difference (ART minus GAT) was 3.0 ± 4.0 mmHg, which increased with increasing mean IOP (p < 0.001). Both GAT IOP and ART IOP readings were significantly directly related to the CCT values (p = 0.03 and p = 0.004, respectively; intermethods difference, p = 0.32). Conclusions: The ART intra‐examiner repeatability was excellent, although significantly lower than that of GAT, and decreased at higher IOP levels. ART significantly overestimated GAT IOP measurements, especially at higher IOP range. Both GAT and ART appeared similarly influenced by CCT value.     

Corneal biomechanics measured with the ocular response analyser in patients with unilateral open‐angle glaucoma

Purpose: To evaluate the relationship between biomechanical properties of the cornea and intraocular pressure (IOP) and the role of biomechanical properties in eyes of patients with unilateral primary open‐angle glaucoma (POAG). Methods: The biomechanical properties of corneal hysteresis (CH) and the corneal resistance factor (CRF) were measured with the ocular response analyser (ORA). In an experimental setting, three human donor eyes with Schiotz‐tonometry‐controlled IOP were investigated. In addition, a series of patients with unilateral POAG were evaluated. Main outcome measures were CH, CRF, corneal‐compensated IOP (IOPcc), standard automated perimetry parameters mean defect (MD) and pattern standard deviation, central corneal thickness, Goldmann applanation tonometry (GAT), and cup‐to‐disc ratio. Results: A highly significant linear correlation between CH and the corneal‐compensated IOP (IOPcc, r = ?0.926; p < 0.001) was found. The correlation between IOP_CC and CRF was not significant (r = 0.335; p = 0.08). In total, 36 eyes of 18 patients with unilateral POAG were examined. Regarding uncorrected CH (mean 7.73 ± 1.46 mmHg glaucomatous eye and 9.28 ± 1.42 mmHg fellow eye), there was a highly significant difference between both eyes. This difference disappears, when CH was corrected for IOP (9.44 ± 3.78 mmHg and 9.97 ± 3.22 mmHg, respectively). Conclusions: Corneal hysteresis but not corneal resistance factor is dependent on IOP. In patients with unilateral POAG, IOP is higher in the affected eye. When CH is corrected for IOP, corneal biomechanical properties do not differ in both eyes of patients with unilateral POAG.     

近视患者中央角膜厚度及其相关因素分析

目的:探讨与近视患者中央角膜厚度相关的因素。方法:近视及近视散光患者2217例(4398眼),用超声角膜测厚仪测量角膜中央厚度,电脑验光仪测量屈光度,非接触眼压计测量眼压,OrbscanⅡ眼前节分析仪查角膜地形图测量角膜曲率,并统计患者性别、年龄及配戴软性角膜接触镜情况。结果:近视患者平均中央角膜厚度为548.57±30.42μm,男女眼之间、左右眼之间、低龄与高龄眼之间平均中央角膜厚度均无统计学差异。中央角膜厚度与屈光度呈正相关(r=0.506,P=0.000)。中央角膜厚度与眼内压呈正相关(r=0.634,P=0.000)。中央角膜厚度与角膜曲率之间无相关性。中央角膜厚度与是否配戴软性角膜接触镜有关,长期持续配戴软性角膜接触镜患者与无角膜接触镜配戴史患者平均中央角膜厚度的差异有显著性(P=0.000)。结论:近视患者中央角膜厚度与屈光度、眼内压及配戴软性角膜接触镜情况等因素有相关性。     

Central corneal thickness and corneal hysteresis during corneal swelling induced by contact lens wear with eye closure

PURPOSE: To determine if corneal hysteresis (CH) was associated with increased central corneal thickness (CCT) induced by wearing soft contact lenses during eye closure. DESIGN: A prospective laboratory investigation. METHODS: CCT was measured with a modified optical coherence tomography (OCT), and CH was measured with a Reichert Ocular Response Analyzer (ORA) [Reichert Ophthalmic Instruments, Depew, New York, USA]. The ORA also determined values for intraocular pressure (IOP), corneal compensated IOP (IOPcc), and corneal resistance factor (CRF). One randomly selected eye of 20 non-contact lens wearers (four males and 16 females, age 19.7 +/- 1.1 years) was patched during three hours of soft contact lens wear. Measurements were made before lens insertion, immediately upon removal, and every 20 minutes thereafter for 100 minutes. RESULTS: Immediately after contact lens removal, CCT was increased by 13.1 +/- 2.2% (mean +/- SD) compared with baseline (post hoc, P = .001). After 100 minutes, it remained elevated by 2.4 +/- 1.6% (post hoc, P = .001). However, there were no significant differences of CH at any time after lens wear (analysis of variance [ANOVA], P = .9). Immediately after lens removal, there were significant increases in IOP (post hoc, P = .003) and corneal resistance factor (CRF) (post-hoc, P = .015), but not in IOPcc (post hoc, P = .07). After lens wear, there were significant but weak correlations between the percentage change of CCT (CCT%) and IOP (r = 0.32, P = .001) and IOPcc (r = 0.29, P = .001). However, there was no significant correlation between CCT% and CH (r = 0.07, P = .458). CONCLUSION: CH as measured by ORA was not associated with corneal swelling induced by soft contact lens wear in this study group.     

Corneal swelling and recovery following wear of thick hydrogel contact lenses in insulin-dependent diabetics

Thick, 0.34 mm, 38% water hydrogel lenses were fitted, under a pressure patch, no one eye of 18 type I diabetic patients (aged 18–40 years) to assess the acute response to hypoxia and hypercapnia; the response was compared with that in 18 healthy, aged-matched non-diabetic subjects; the closed-eye lens wear was started mid-morning. Pre-lens wear assessments were made of acuity, intraocular pressure (IOP), central corneal thickness (CCT) and corneal appearance by biomicroscopy. The mean duration of the diabetes was 13 ± 7 years and the average fasting blood glucose was 8.7 ± 3.3 mM l^?1. Baseline CCT values were marginally greater in diabetic patients (600 ± 33 μm) compared with a group of non-diabetic control subjects (584 ± 26 μm; P > 0.5). A 7.7 ± 2.1% increase in CCT was measured after 3 h lens wear in the diabetic patients while an average 10.6 ± 2.4% increase in CCT was measured in the control subjects (P < 0.05). The recovery of corneal thickness to baseline values in diabetic patients was slower (at 44.8 ± 2.0% per hour) than the control subjects (53.9 ± 2.1 per hour; P < 0.05) although recovery of corneal thickness occurred in both groups within 2.5–3 h. IOP values (non-contact tonometry) were higher in the diabetic patients than in the controls (14.5 ± 2.9 vs 12.4 ± 1.7 mmHg; P < 0.01). Overall, those corneas with greater baseline CCT values tended to swell less than those with lower baseline CCT values (r = 0.582). Positive correlations were also found between corneal thickness and IOP and blood glucose. The diabetic patients thus tended to have slightly thicker corneas (but this could be related to blood glucose or IOP rather than true corneal disease) and also had corneas that tended to swell less with a contact lens stress test (but this could be constitutively due to the slight oedema already present). The different corneal response in diabetic patients may thus be the result of physical determinants such as initial oedema and IOP and not the result of a disease of the cornea itself.     

Corneal thickness and corneal endothelium in normotensive subjects with unilateral exfoliation syndrome

Purpose: To examine the central corneal thickness (CCT) and corneal endothelium in both eyes of patients with unilateral exfoliation syndrome (EXS). To determine the effect of CCT on the measurement of intraocular pressure (IOP). Methods: In this cross-sectional clinical study, comparisons were made of CCT (Humphrey Ultrasonic Pachometer), corneal endothelial cells (Keeler-Konan contact specular microscope) and IOP (Goldmann applanation tonometer) between the exfoliative (E) and fellow non- exfoliative (NE) eyes in 40 normotensive patients with unilateral EXS. The CCT was used to obtain a corrected value for the IOP. Results: The E eyes had significantly higher values for CCT (0.528±0.030 vs 0.523±0.032 mm, P<0.01) and IOP (15.7±3.6 vs 14.4±2.9 mmHg, P<0.001) than the fellow NE eyes. The paired E and NE eyes did not differ in endothelial cell density (2779±540 vs 2870±386 cells/mm²), in the coefficient of variation of cell size (0.25±0.03 vs 0.26±0.03) or in the frequency of hexagonal cells (80.5±6.5 vs 82.0±5.0%). After correcting IOP for CCT, the E eyes still had significantly higher IOP than the NE eyes (15.1±4.4 vs 14.2±3.7 mmHg, P<0.05). Conclusion: Normotensive eyes with early EXS did not have quantitative (cell density) or qualitative (variation in cell size, frequency of hexagonal cells) morphological changes in corneal endothelium, but had higher values for IOP and CCT. After correcting IOP for CCT, the E eyes still had significantly higher IOP than the fellow NE eyes. Received: 16 December 1999 Revised: 20 March 2000 Accepted: 21 March 2000     

The ocular pulse amplitude at different intraocular pressure: a prospective study

Purpose: To investigate changes in ocular pulse amplitude (OPA) during a short‐term increase in intraocular pressure (IOP) and to assess possible influences of biometrical properties of the eye, including central corneal thickness (CCT) and axial length. Methods: In a prospective, single centre study, OPA and IOP as measured by dynamic contour tonometry (DCT) were taken before baseline‐ and post‐OPA (delta) intravitreal injection of 0.05 ml anti‐vascular endothelial growth factor agents. Analysis was performed employing linear regression with baseline‐ and post (delta)‐OPA differences as the dependent and post‐IOP as well as delta IOP as the independent variable. A multilinear regression analysis with delta OPA as the dependent variable and baseline IOP, post‐IOP, CCT and axial length as independent variables was conducted. Results: Forty eyes of 40 patients were included. IOP and OPA increased significantly after injection (IOP mean increase ± SD: 17.83 ± 9.83 mmHg, p < 0.001; OPA mean increase ± SD: 1.39 ± 1.16 mmHg, p < 0.001). For every mmHg increase in IOP, the OPA showed a linear increase of 0.05 mmHg (slope 0.05, 95% CI: 0.02–0.09, p = 0.003, r² = 0.20). Multiple regression analysis with delta OPA as the dependent variable revealed a partial correlation coefficient of 0.47 (p = 0.003) for post‐IOP as the only significant contribution. Conclusion: A clear positive relationship between OPA measurements and IOP levels was shown in a clinical routine setting using DCT focusing on baseline and postinterventional comparisons of OPA values after intravitreal injections in patients with exudative age related macular degeneration. When considering the OPA for diagnostic purposes, we recommend indication of corresponding IOP values.     

Comparison of IOP measurements between ORA and GAT in normal Chinese.

PURPOSE: To compare intraocular pressure (IOP) obtained from the ocular response analyzer (ORA) and Goldmann applanation tonometer (GAT) on a group of normal Chinese. METHODS: One hundred twenty-five normal subjects were recruited, with one eye randomly selected for this study. Each eye was measured first with the noncontact tonometer ORA, followed by the GAT and ultrasound pachometry, in a randomized order. Four readings were obtained from the ORA, and three measurements were taken with the GAT. The mean was used for analysis. The ORA provided a Goldmann-correlated IOP (IOPg) and a corneal-compensated IOP (IOPcc). Three central corneal thickness (CCT) values were measured using an ultrasound pachometer, and the mean was used for analysis. RESULTS: IOP obtained from the ORA was similar to that from the GAT (IOPg minus GAT: mean difference = 0.33 mm Hg, 95% limits of agreement = 4.55 to -4.44 mm Hg; IOPcc minus GAT: mean difference = 0.24 mm Hg, 95% limits of agreement = 4.83 to -5.07 mm Hg). CCT was positively associated with corneal hysteresis (CH) (r2 = 0.30, p < 0.01), corneal resistance factor (r2 = 0.38, p < 0.01), GAT (r2 = 0.09, p < 0.01) and IOPg (r2 = 0.16, p < 0.01). IOPcc was not associated with CCT (r2 = 0.01, p = 0.33). CONCLUSIONS: Both IOPg and IOPcc have good agreement with GAT on normal subjects. The influence of CCT on IOPcc was insignificant.     

The effect of corneal edema on dynamic contour and goldmann tonometry

PURPOSE: To determine the effect of contact lens-induced corneal edema on measurements of intraocular pressure (IOP) using the Pascal dynamic contour tonometer (DCT), compared with the Goldmann tonometer. METHODS: Thirty young healthy subjects (23.0 +/- 3.0 years) were recruited from the student population at the University of New South Wales. Thick hydroxyethyl methacrylate contact lenses were worn monocularly for 2 hours under closed-eye conditions to induce corneal edema via hypoxia. IOP (Goldmann and Pascal DCT), ocular pulse amplitude (OPA), and central corneal thickness (CCT) were measured in both eyes before and after lens wear. Paired t-tests, Pearson correlation, and Bland-Altman plots were used to identify changes in, and relationships between, these parameters resulting from corneal edema. RESULTS: Lens wear resulted in statistically significant changes in CCT (+48.3 +/- 14.4 microm, p < 0.001), Goldmann IOP (+1.5 +/- 2.8 mm Hg, p = 0.007), and Pascal DCT IOP (-0.7 +/- 1.1 mm Hg, p = 0.001) but not OPA (0.0 +/- 0.3 mm Hg, p = 0.721, two-tailed paired t-test). The Pascal DCT provided IOP readings that were 1.3 +/- 2.0 mm Hg higher than the Goldmann IOP readings when hydration was normal, but the Goldmann tonometer provided readings that were 0.8 +/- 2.5 mm Hg higher than the Pascal DCT readings when the cornea was edematous. The variation between the two instruments was weakly correlated to the change in CCT (r = -0.261, p = 0.044). CONCLUSIONS: Contact lens-induced corneal edema caused a small underestimation error in IOP measurements by the Pascal DCT, and an overestimation error in Goldmann tonometry measurements. The OPA measurement provided by the Pascal DCT is insensitive to corneal edema-induced changes in corneal properties.     

Diurnal variation of central corneal thickness and Goldmann applanation tonometry estimates of intraocular pressure

PURPOSE: To determine whether there is a temporal relationship between the diurnal variation of central corneal thickness (CCT) and intraocular pressure (IOP) by Goldmann applanation tonometry in young normal human participants in vivo. METHODS: Twenty-five eyes of 25 young healthy normal participants were examined in a prospective observational cross-sectional study. IOP, CCT and corneal curvature were measured using standard clinical techniques over a 24-hour period, and the temporal interrelationships between these parameters were examined. RESULTS: The overnight change in IOP measured by Goldmann tonometry was 3.1+/-2.4 mm Hg (P<0.001), CCT was 20.1+/-10.9 mum (P=0.016), with no statistical change in central corneal curvature (0.05 mm, P=0.477, paired t test with Bonferroni correction). Both IOP and CCT were highest on awakening at 7:00 then dropped rapidly to baseline levels by 9:00 (linear mixed models), and these two parameters were highly correlated (r=0.978, P<0.001). After 9:00, there was no correlation between these parameters (r=-0.453, P=0.260). CONCLUSIONS: The results of this study have highlighted a potential link between the diurnal variation of CCT and the accuracy of Goldmann tonometry estimates of IOP during the first 2 hours after awakening. Clinicians should be wary of using Goldmann tonometry to estimate IOP until the overnight increase in CCT has resolved.     

Corneal hysteresis measured with the Ocular Response Analyzer® in normal and glaucomatous eyes

Purpose: To identify differences in corneal hysteresis (CH) and central corneal thickness (CCT) between healthy and glaucomatous patients. Methods: Retrospective observational study. One hundred and thirty‐three eyes of 75 healthy and 58 glaucomatous patients were included. CH was measured in each patient using Ocular Response Analyzer. CCT was determined by ultrasonic pachymetry. For each patient, one eye was randomly selected. We used a Student t‐test to search for significant differences between the different groups (p<0.05). Results: In healthy and glaucomatous eyes, mean CH values were 10.46 ± 1.6 and 8.77 ± 1.4 mm Hg, respectively. Mean CCT values were 560.2 ± 36.3 and 535.3 ± 42.7 μm, respectively. CH and CCT were significantly lower in glaucomatous eyes than in normal eyes, (p<0.05). Discussion: In our series, CH was lower in glaucomatous than in normal eyes. The relationship between glaucoma, IOP, and ocular structures may not be confined to the consideration of CCT. A low CH value could be responsible for under‐estimation of IOP. CH could also be a risk factor for glaucoma, independent of IOP. Further studies are needed to support these hypotheses. Conclusion: In our investigation, CCT and CH were significantly lower in glaucomatous eyes than in healthy eyes.     

Central corneal thickness and visual field loss in fellow eyes of patients with open-angle glaucoma

PURPOSE: To determine the relationship of central corneal thickness (CCT) and visual field loss between fellow eyes in primary open-angle glaucoma. DESIGN: Retrospective, observational case series. METHODS: Records review of glaucoma patients seen at local Veterans Administration eye clinic. Those with CCT measurements performed within one month of visual field testing were included. Patients were excluded with vision below 20/40 or disease that would affect visual fields. Intrasubject (between fellow eyes) differences in CCT, mean deviation (MD), and pattern standard deviation (PSD) were calculated by subtracting left eye value from right eye value. RESULTS: Of the 100 subjects (94 males), the Spearman correlation coefficient between intrasubject differences in CCT vs intrasubject differences in MD was 0.36 (P = .0003). The Spearman correlation for differences in CCT vs differences in PSD was -0.31 (P = .0019). CONCLUSIONS: Our study suggests that worse visual field changes tend to occur in the eye with the thinner cornea.     

Evaluation of anterior segment parameter changes using the Pentacam after uneventful phacoemulsification

Purpose: This study set out to evaluate the influences of uneventful phacoemulsification on the anterior segment parameters obtained with the Pentacam rotating Scheimpflug camera and intraocular pressure (IOP). Methods: A total of 42 eyes of 34 patients (26 men, eight women) were evaluated preoperatively, and at 1, 3 and 6 months postoperatively with the Pentacam. Intraocular pressure was measured with the Goldmann applanation tonometer. The non‐parametric paired t‐test was used to compare preoperative and 1‐, 3‐ and 6‐month postoperative measurements of anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA) width, central corneal thickness (CCT), the central 3‐, 5‐ and 7‐mm corneal volume (CV), pupil size, and IOP. Pearson’s correlation test was used to evaluate the relationships between IOP and ACD, ACV and ACA width. Results: The differences between ACD, ACV, ACA and IOP values taken preoperatively and those taken postoperatively at 1, 3 and 6 months were statistically significant (p < 0.05). The differences between CCT, central 3‐, 5‐ and 7‐mm CV, and pupil size measurements taken preoperatively and those taken postoperatively at 1, 3 and 6 months were not statistically significant (p > 0.05). The decrease in IOP was not correlated with the changes in ACD, ACV and ACA (p > 0.05). Conclusions: Uneventful phacoemulsification significantly reduced IOP, increased ACD and ACV, and widened the ACA. However, alterations in CV, CCT and pupil size values were not statistically significant. Alterations in ACD, ACV, ACA and IOP remain stable after the first month of surgery.     

Effect of corneal thickness on intraocular pressure measurements with the Pascal dynamic contour,Canon TX‐10 non‐contact and Goldmann applanation tonometers in healthy subjects

Purpose: To investigate the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measurements of the Pascal dynamic contour tonometry (DCT), Canon TX‐10 non‐contact tonometry (NCT) and Goldmann applanation tonometry measurements (GAT) in healthy subjects. Methods: IOP values of 135 eyes with normal corneas of 135 healthy volunteers were determined by DCT, NCT and by GAT. The CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made. Results: When DCT measurements were compared (IOP = 17.52 ± 2.0 mmHg) with NCT measurements (IOP = 16.54 ± 2.77 mmHg) and GAT measurements (IOP = 15.07 ± 2.35 mmHg), DCT measurements were significantly higher than NCT and GAT (p < 0.001). There was a significant correlation between CCT with both NCT (r = 0.260, p = 0.003) and GAT measurements (r = 0.257, p = 0.005). There was a weak correlation that was not statistically significant between CCT and DCT (r = 0.160, p = 0.079). Conclusion: The IOP measurements with DCT seem to be less dependent on CCT. NCT appears to be more affected by variation in CCT than GAT.     

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

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

兔眼中央角膜厚度与Perkins压平眼压关系的研究

目的探讨中央角膜厚度(CCT)与Perkins压平眼压的关系,建立CCT、真实眼压与Perkins压平眼压三者关系的数学模型和CCT对Perkins压平眼压的校正公式。方法健康新西兰大耳白兔32只,双眼中1只眼行准分子激光屈光性角膜切削术(PRK),另1只眼测得的数据对行PRK眼得出的数据进行验证。采用随机数字表法随机取1只眼,采用PRK,人为改变兔眼的CCT,建立不同CCT的活体眼模型,分别采用Perkins压平眼压计、A型超声角膜测厚仪、角膜曲率计测量术前、术后Perkins压平眼压、CCT、角膜曲率以及应用电子直接眼压计测量真实眼压,分别对术前和术后测量值做相关分析和多元线性回归分析,并对另1组未行PRK眼测得的真实眼压、Perkins压平眼压、CCT对实验组得出的公式进行验证。结果兔眼双眼Perkins压平眼压、CCT、角膜曲率无统计学差别,无论是术前还是术后Perkins压平眼压与CCT均显著相关(r=0.761P<0.01;r=0.829,P<0.01),与角膜曲率无关(r=0.098,P>0.05;r=0.260P>0.05)。对术前、术后Perkins压平眼压与CCT建立回归公式,曲线的斜率分别为0.066、0.053,Perkins压平眼压的改变与CCT的改变有关。对真实眼压Y与Perkins压平眼压、CCT三者的关系建立回归公式为Y=12.107+1.254X1-0.033X2(X1=Perkins压平眼压,X2=CCT)。结论CCT的改变影响Perkins压平眼压的测量值,临床上应根据CCT来校正Perkins压平眼压的测量值。