Clinical study of the influence of diabetes mellitus on corneal health

Central corneal thickness in children—does it help or hinder our evaluation of eyes at risk for glaucoma?

To assess the effect of overnight wear of a contact lens-based sensor (CLS) for monitoring of 24-hr intraocular pressure (IOP) fluctuations on central corneal thickness (CCT). Changes in the CCT, mid-peripheral corneal thickness and central corneal radius (CCR) during overnight CLS wear in 20 eligible patients with ocular hypertension or established glaucoma were prospectively studied using ultrasound pachymetry and topography. Corneal thickness and CCR changes were evaluated from pre-to-postsleep, with the fellow eye as control. Paired t-test or Wilcoxon signed-rank test was used as appropriate and with α = 0.05. Relationship between the IOP profile recorded by the CLS and the pre-to-postsleep corneal thickness differences was assessed using the Spearman correlation coefficient. After CLS wear, mean CCT had changed from 523 to 537 μm (p = 0.015) in the study eye and from 518 to 522 (p = 0.206) in the fellow eye (n = 15). There was no difference in CCT change between eyes (p = 0.075). There were no statistically significant changes in horizontal or vertical CCR in either eye (p > 0.05 for all). No correlation was found between the pre-to-postsleep differences in the CLS signal and the pre-to-postsleep differences in ultrasound CCT measurements (p = 0.974). The continuous IOP monitoring does not appear to be affected by differences in corneal thickness that occur during overnight CLS wear, although the CLS did induce some corneal swelling. This effect was not statistically significantly different from the control eye and does not seem to influence the CLS IOP profile.

To investigate the accuracy of intraocular pressure (IOP) as measured by a Reichert Ocular Response Analyzer (ORA), as well as the relationship between central corneal thickness (CCT) and IOP as measured by ORA, Goldmann applanation tonometry (GAT), and dynamic contour tonometry (DCT). A total of 158 healthy individuals (296 eyes) were chosen randomly for measurement of IOP. After CCT was measured using A-ultrasound (A-US), IOP was measured by ORA, GAT, and DCT devices in a randomized order. The IOP values acquired using each of the three tonometries were compared, and the relationship between CCT and IOP values were analyzed separately. Two IOP values, Goldmann-correlated IOP value (IOPg) and corneal-compensated intraocular pressure (IOPcc), were got using ORA. Three groups were defined according to CCT: 1) thin cornea (CCT<520µm); 2) normal-thickness cornea (CCT: 520-580µm); and 3) thick cornea (CCT>580µm) groups. In normal subjects, IOP measurements were 14.95±2.99mmHg with ORA (IOPg), 15.21±2.77mmHg with ORA (IOPcc), 15.22±2.77mmHg with GAT, and 15.49±2.56mmHg with DCT. Mean differences were 0.01±2.29mmHg between IOPcc and GAT (P>0.05) and 0.28±2.20mmHg between IOPcc and DCT (P>0.05). There was a greater correlation between IOPcc and DCT (r=0.946, P=0.000) than that between IOPcc and GAT (r=0.845, P=0.000). DCT had a significant correlation with GAT (r=0.854, P=0.000). GAT was moderately correlated with CCT (r=0.296, P<0.001), while IOPcc showed a weak but significant correlation with CCT (r=-0.155, P=0.007). There was a strong negative correlation between CCT and the difference between IOPcc and GAT(r=-0.803, P=0.000), with every 10µm increase in CCT resulting in an increase in this difference of 0.35mmHg. The thick cornea group (CCT>580µm) showed the least significant correlation between IOPcc and GAT (r=0.859, P=0.000); while the thin cornea group (CCT<520µm) had the most significant correlation between IOPcc and GAT (r=0.926, P=0.000). The correlated differences between IOPcc and DCT were not significant in any of the three groups (P>0.05). Measurement of IOP by ORA has high repeatability and is largely consistent with GAT measurements. Moreover, the ORA measurements are affected only to a small extent by CCT, and are likely to be much closer to the real IOP value than GAT.

The effect of the design and fitting ofsoft lenses on corneal physiology

Human Corneal Thickness and Its Impact on Intraocular Pressure Measures: A Review and Meta-analysis Approach

Background: Diabetic retinopathy (DR) is one of the most common causes of preventable blindness. Patients with Diabetes Mellitus (DM) develop not only DR but also corneal endothelial damage leading to anatomical and physiological changes in cornea. Central corneal thickness (CCT) is a key parameter of refractive surgery and Intraocular pressure (IOP) estimation. The role of CCT and higher glycemic index in DR needs to be researched upon. Objectives: To identify the corneal endothelial morphology in patients with type 2 DM, to measure the Central Corneal thickness (CCT) in patients with type 2 Diabetes Mellitus, to assess the relationship of CCT with HbA1C levels in the study group and to correlate the CCT with the severity of Diabetic retinopathy in the study group. Methods: A cross-sectional observational study was conducted between January 2018 and June 2019 in Vydehi Institute of Medical Sciences and Research Centre, Bangalore. The study included 100 subjects with type 2 DM for 5 years or more. Patients with comorbidities that may affect the severity of DR or alter CCT and other corneal endothelial parameters such as glaucoma, previous ocular surgery or trauma, corneal degenerations and dystrophies, chronic kidney disease and Hypertension were excluded. DR was assessed by dilated fundoscopy, fundus photography and optical coherence imaging of the macula and graded as per the Early Treatment of Diabetic Retinopathy Study (ETDRS) classification. CCT and other corneal endothelial parameters were measured through specular microscopy. Relevant blood investigations including blood sugar levels were done for all patients. Statistical analysis: Relationship between CCT and grades of DR and HbA1c levels were established using the Chi-Square test. The level of significance was set at p &lt; 0.05. Results: The mean CCT in patients with no diabetic retinopathy, very mild and mild non-proliferative diabetic retinopathy (NPDR), moderate NPDR, severe and very severe NPDR and PDR was 526.62 ± 8.084 μm, 542.07 ± 8.713 μm, 562.16 ± 8.255 μm, 582.79 ± 7.368 μm and 610.43 ± 18.256 μm respectively. Analysis of the relationship between CCT and severity of DR showed a statistically significant positive correlation between the two parameters (Pearson r = 0.933, P=0.001). Beyond this, a correlation was found between all the corneal endothelial parameters and severity of DR. Multivariate analysis showed that advanced DR was positively correlated with CV (r = 0.917) and CCT (r = 0.933); while it was negatively correlated with ECD (r = -0.872) and Hex (r = -0.811). A statistically significant correlation was also found between CCT and HbA1c. Also increasing age, duration of DM and higher glycemic index were positively correlated with severity of DR. Conclusion: This study, by demonstrating a strong correlation between the central corneal thickness to the severity of DR and HbA1c levels emphasizes the importance of evaluation of corneal endothelial morphology in the early screening and diagnosis of microvascular complications of DM.

To compare intraocular pressure (IOP) measurements taken with Pascal dynamic contour tonometry (DCT), the TonoPen and the Goldmann applanation tonometry (GAT). The influence of central corneal thickness (CCT) on IOP measurements taken with Pascal DCT and the TonoPen was evaluated. One eye in each of 101 consecutive patients with primary open-angle glaucoma (POAG) underwent ultrasonic CCT measurement and IOP evaluation with GAT, Pascal DCT and the TonoPen in random order. The agreement between results from Pascal DCT and the TonoPen and those of GAT was assessed using the Bland-Altman method. The deviation of Pascal DCT and TonoPen readings from GAT values, corrected for CCT, was calculated and correlated to CCT using a linear regression model. The mean of the differences in IOP measurements was 3.2 +/- 2.4 mmHg for Pascal DCT minus GAT readings and 0.5 +/- 4.5 mmHg for TonoPen minus GAT readings. The 95% confidence interval of differences in IOP measurements was higher between TonoPen and GAT readings (- 6 to 7 mmHg) than between Pascal and GAT readings (0.1-6.8 mmHg). Pascal DCT significantly overestimated IOP compared with GAT, especially for higher IOP readings. Bland-Altman scatterplots showed reasonable inter-method agreement between Pascal DCT and GAT measurements, and poor agreement between TonoPen and GAT measurements. The deviations of Pascal DCT and TonoPen readings from the corrected GAT values were both highly correlated with CCT values (linear regression analysis, p < 0.0001). The mean change in measured IOP for a 10-microm increase in CCT was 0.48 mmHg for Pascal DCT and 0.74 mmHg for the TonoPen. Agreement with GAT measurements was higher for Pascal DCT than for TonoPen readings; however, Pascal DCT significantly overestimated IOP values compared with GAT. Measurements of IOP obtained with both Pascal DCT and the TonoPen appeared to be influenced by CCT, and this influence appeared to be greater for the latter.

To compare the changes of central corneal thickness (CCT) and intraocular pressure (IOP) post-phacoemulsification between cataract patients with and without pre-existing glaucoma. A prospective cohort study of 86 patients with visually significant cataract: 43 with pre-existing glaucoma (GC group) and 43 without pre-existing glaucoma (CO group). CCT and IOP were evaluated at baseline (pre-phacoemulsification), as well as at 2 hours, 1 day, 1 week and 6 weeks post-phacoemulsification. The GC group have significantly thinner CCT pre-operatively (p = 0.003). There was a steady increase of CCT with the highest peak at 1 day post-phacoemulsification, followed by a steady decline of CCT and back to baseline at 6 weeks post-phacoemulsification in both groups. The GC group demonstrated a significant difference in CCT at 2 hours (mean difference 60.2 μm, p = 0.003) and 1 day (mean difference 70.6 μm, p = 0.002) post-phacoemulsification, compared to the CO group. There was a sudden increase in IOP at 2 hours post-phacoemulsification measured by GAT and DCT in both groups. This was followed by a gradual reduction of IOP, with significant reduction at 6 weeks post-phacoemulsification in both groups. However, there was no significant difference in IOP between the two groups. IOP measured by GAT and DCT showed strong correlation (r &gt; 0.75, p &lt; 0.001) in both groups. There was no significant correlation between GAT-IOP and CCT changes; nor between DCT-IOP and CCT changes in both groups. CCT changes post-phacoemulsification in patients with pre-existing glaucoma were similar, in spite of having thinner CCT pre-operatively. IOP measurement was not affected by CCT changes in glaucoma patients post-phacoemulsification. IOP measurement using GAT is comparable with DCT post-phacoemulsification.

Intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT) are influenced by central corneal thickness (CCT) whereas dynamic contour tonometry (DCT) allows for IOP measurements independent of CCT. After Descemet's stripping automated endothelial keratoplasty (DSAEK) the CCT is, compared to healthy eyes, increased. The objective of this prospective study was to compare IOP measurements obtained by DCT and GAT in patients after a DSAEK procedure. DCT and GAT were performed 3 and/or 6 months after DSAEK. Comparison of means was performed using the Wilcoxon signed-ranks test. In total, 50 IOP measurements on 33 eyes were obtained. Mean CCT was 621 (+/- 60) microm. Overall correlation between GAT and DCT was good, however, in some patients a remarkable difference between pressure readings of up to 10.8 mmHg was observed. Mean IOP readings obtained by DCT were significantly higher (20.9 +/- 5.9 mmHg) than those obtained by GAT (19.1 +/- 6.5 mmHg; p = 0.0002). However, the difference between GAT and DCT readings was not influenced by the thickness of the transplanted lamella. The well-known difference in mean pressure readings between DCT and GAT was not affected by the increase in CCT following DSAEK. IOP readings with the GAT seem not to be influenced by the increase in CCT. Because of the remarkable differences in individual pairs of IOP measurements, both GAT and DCT should be used after DSAEK.

Background: The aim of this study was to investigate the relationship between Goldmann applanation tonometry and central corneal thickness in a large sample of healthy eyes. Method: Five hundred eyes of 500 subjects (253 women, 50.6 per cent and 247 men, 49.4 per cent) were analysed in a prospective healthy population study. Mean age of the sample was 31 ± 8 years. Goldmann applanation tonometry was carried out by one physician. Tonometric values were the mean of three consecutive readings. Subsequently, another physician carried out ultrasonic pachymetry with the DGH 2000 AP ultrasonic pachymeter (DGH Technology Inc, San Diego, USA). Ten measurements were made at the centre of the cornea of each eye. The lowest value was used for analysis. Results: Applanation tonometry and central corneal thickness were correlated (r = 0.184, p < 0.001). There was no significam correlation between corneal thickness and age (r = 0.083, p = 0.065), mean spherical equivalem refraction (r = 0.083, p = 0.065) or visual acuity (r = 0.036, p = 0.187). Conclusion: In normal eyes, there is no statistically significant correlation between changes of intraocular pressure and changes of central corneal thickness but they suggest a relationship between intraocular pressure and central corneal thickness. Goldmann applanation tonometry has a systematic error in accuracy of intraocular pressure readings of healthy eyes caused by its dependence on central corneal thickness. Measurement of corneal thickness by optometrists should be the first step in diagnosing intraocular pressure pathologies.

BackgroundTo compare intraocular pressure (IOP) measurements obtained with the Topcon CT‐80 non‐contact tonometer (NCT) and Goldmann applanation tonometer (GAT), in different ranges of IOP in normal and glaucoma subjects, and to assess the influence of central corneal thickness (CCT) on the IOP measurements in Asian Indian eyes.MethodsFour hundred and two eyes of 402 subjects (193 newly diagnosed primary open angle glaucoma [POAG] and 209 normal) were enrolled for this prospective study. For each eye, IOP was measured with GAT by a glaucoma specialist and NCT by a trained optometrist. The IOP values were compared among the tonometers in the three different IOP ranges (≤ 12 mmHg, 13–20 mmHg and ≥ 21 mmHg) using Bland–Altman graphs. Correlation between GAT and NCT was assessed by Pearson correlation co‐efficient. CCT was measured with ultrasound pachymetry and its correlation with GAT and NCT was analysed using linear regression analysis.ResultsThe mean paired difference of IOP between NCT and GAT was 1.556 ± 2.69 mmHg (r = 0.26, p = 0.006) at IOP range of ≤ 12 mmHg, −1.665 ± 2.6 mmHg (r = 0.51, p < 0.0001) in IOP range of 13–20 mmHg and −2.202 ± 3.44 mmHg (r = 0.82, p < 0.0001) in the IOP range of ≥ 21 mmHg. Linear regression analysis showed a mean IOP variation of 0.27 mmHg per 10 μm change in CCT for NCT (p < 0.0001) and IOP change of 0.19 mmHg per 10 μm change in CCT for GAT (p = 0.01).ConclusionIn this study of normotensive and POAG subjects, the Topcon CT‐80 NCT showed an overestimation of IOP at the lower range and underestimation of IOP in normal and higher ranges of IOP. Clinicians should keep in mind that CCT influences IOP measurement with both types of tonometer and that the IOP readings obtained with these tonometers are not interchangeable.

Corneal Thickness and Glaucoma Medications

To determine the effects of central corneal thickness (CCT), central corneal power (CCP), and axial length (AL) on the measurement of intraocular pressure (IOP) using Goldmann applanation tonometry, and the effects of CCP and AL on CCT. Charts of 147 consecutive patients undergoing preoperative examinations for cataract surgery between April 2006 and April 2007 in our clinic were reviewed retrospectively. CCT, CCP, and AL were measured by ultrasonic pachymeter (Micropach Model 200P, Sonomed, Lake Success, N.Y. USA), autorefractokeratometer (KR 8800, Topcon, Tokyo, Japan), and ultrasound biometry (EZ Scan AB 5500+ Sonomed, Lake Success, N.Y. USA). Pearson correlation analysis and multiple linear regression analysis were used as indicated, and only one eye of each subject was included in the statistical analysis. Ninety-eight eyes of 98 patients were included in the study. IOP and CCT were significantly and positively correlated (P<0.001), and CCT and CCP (P=0.001) were inversely correlated. Multiple regression analysis showed that the effect of CCT on IOP was statistically significant (P<0.001), but the effects of CCP and AL on IOP were not significant (P=0.614, P=0.831, respectively). IOP increased by 0.29 mmHg for each 10 microm increase in CCT. CCT, but not CCP or AL, significantly affected IOP readings obtained by Goldmann applanation tonometry. The effect of CCP on IOP was weak and not significant despite the significant inverse correlation between CCT and CCP.

Tono-Pen versus Goldmann Applanation Tonometry: A Comparison of 898 Eyes

Cataract surgery in patients with diabetes