Effect of diabetes mellitus on Corvis ST measurement process

The corneal biomechanical changes of phacoemulsification in cataract patients: A systematic review and meta-analysis

PURPOSE

To evaluate the corneal biomechanical properties of phacoemulsification in the treatment of cataract patients.

METHODS

Pertinent studies were searched in PubMed, EMBASE, Web of Science and clinicaltrials.gov., as of November 05, 2024. The reference lists of related published reviews were included as well. This meta-analysis was performed with Stata Software and Review Manager, we used mean difference (MD) to evaluate the statistical consequence, using I2 statistic to assess the heterogeneity. Subgroup analysis were performed under the occurrences of high heterogeneity. We used eleven items to describe the characteristics of included studies, publication bias was performed with Egger's test. The quality assessment were evaluated with 3 items by Newcastle-Ottawa Scale (NOS) items.

RESULTS

Thirteen eligible studies were identified for data synthesis and assessment. According to the result of meta-analysis, the central corneal thickness(CCT) (MD = 10.50, 95% CI: [5.01, 15.98]; P<0.05) and intraocular pressure(IOPg)(MD = -0.73, 95% CI: [-1.26, -0.19]; P<0.05) of cataract patients after phacoemulsification was significantly higher than the control groups. The values of corneal hysteresis(CH) (MD = -0.43, 95% CI: [-0.62, -0.23]; P<0.05) and corneal resistance factor(CRF) (MD = -0.49, 95% CI: [-0.64, -0.33]; P<0.05) after phacoemulsification surgery were statistically lower than the control groups. While the values of IOPcc did not show statistically different (MD = -0.13, 95% CI: [-0.67, 0.41]; P = 0.64).

CONCLUSION

Included data analysis indicated that the values of CCT, CH, CRF and IOPg showed statistical change in cataract patients after phacoemulsification surgeries compared with control groups. There is a correlation between corneal biomechanics and phacoemulsification surgeries.

Evaluation of a New Diabetes Mellitus Index Based on Measurements Using the Scheimpflug Analyzer Corvis ST

PURPOSE

Chronic hyperglycemia causes changes in corneal biomechanics that can be measured with the Scheimpflug Analyzer Corvis ST. The diagnostic reliability of the new diabetes mellitus (DM) index developed based on this should be evaluated.

METHODS

In a prospective cross-sectional study, the index was initially developed using data from 81 patients with DM and 75 healthy subjects based on logistic regression analysis. The reliability of the DM index was subsequently assessed using data from another 61 patients and 37 healthy individuals. In addition, the dependence of the DM index on indicators of disease severity was analyzed.

RESULTS

The index initially achieved a sensitivity of 79% and specificity of 80% with a cutoff value of 0.58. The evaluation showed a sensitivity of 67% and specificity of 76% with an optimized cutoff of 0.51 (area under the curve = 0.737, P < 0.001). The DM index correlated weakly with the severity of diabetic retinopathy (r = 0.209, P = 0.014). It was increased in the presence of diabetic maculopathy (P = 0.037) and in type 1 DM compared with patients with type 2 disease (P = 0.039).

CONCLUSIONS

In this first evaluation, the new DM index achieved sufficiently good sensitivity and specificity and was weakly associated with disease-specific factors. With further improvements, it could complement the diagnostic options in DM with a simple, rapid, and noninvasive assessment method.

The Effect of Diabetic Retinopathy and Blood Glucose Regulation on Corneal Biomechanical Parameters

PURPOSE

The aim of this study was to evaluate the effects of different stages of diabetic retinopathy (DR) and metabolic control of blood glucose levels on corneal biomechanical parameters.

METHODS

Diabetic patients were categorized into three groups: no DR group, nonproliferative DR (NPDR) group, and proliferative DR (PDR) group. Of the 141 eyes examined, 40 belonged to the control group, 34 to no DR group, 34 to NPDR group, and 33 to PDR group. Using an Ocular Response Analyzer to measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated IOP (IOPcc). IOP was assessed using a Tono-Pen, while central corneal thickness (CCT) was determined using an ultrasonic pachymeter. HbA1c levels were also recorded. We conducted comparisons among these groups across biomechanical parameters and IOP (tonopen), and CCT, while also investigating the impact of HbA1c levels on these parameters.

RESULTS

Among any groups show a statistically significant difference in CCT, IOP (tonopen), CH, CRF, IOPg, and IOPcc. In diabetic patients, CRF, CTT, and IOPg values were significantly higher in those with HbA1c levels ≥ 7 mg/dl than in those with HbA1c levels < 7 mg/dl (p = 0.009, p = 0.013, p = 0.038), respectively, while there was no statistically significant difference in IOPcc, CH, and IOP (tonopen). Linear regression analysis showed that CH was positively associated with CCT (p < 0.001) and negatively associated with IOPcc (p < 0.001), while CRF was positively associated with CCT (p < 0.001), HbA1c (p < 0.05), and negatively associated with diagnosis of DR (p < 0.05).

CONCLUSION

This study underscores the influence of metabolic control, as reflected by HbA1c levels, on corneal biomechanical parameters in diabetic patients, emphasizing the importance of monitoring and managing glycemic control in this population.

Intraocular pressure measurement and association with corneal biomechanics in patients underwent Descemet's stripping with endothelial keratoplasty: a comparative study

Purpose

To compare corneal biomechanical properties and intraocular pressure (IOP) measurements in patients who underwent Descemet's stripping with endothelial keratoplasty (DSEK) with those of the follow healthy eyes.

Methods

In this retrospective comparative study, a total of 35 eyes of 35 patients who underwent DSEK by a single surgeon from 2015.02 to 2019.12 were enrolled along with their fellow healthy eyes. Corneal biomechanical parameters were assessed at least 3 months post-DSEK using Corneal Visualization Scheimpflug Technology (CST). IOP was measured by CST, Goldmann applanation tonometry (GAT), and MacKay-Marg tonometer.

Results

Central corneal thickness (CCT) and stiffness parameter at first applanation (SP-A1) were significantly increased after DSEK when compared to the fellow eyes. In DSEK eyes, biomechanically-corrected intraocular pressure (bIOP) and MacKay-Marg IOP correlated significantly with GAT IOP measurements, with bIOP showed the lowest IOP values. All the IOP values did not correlate with CCT. However, GAT-IOP and MacKay-Marg IOP showed a positive correlation with SP-A1.

Conclusion

The corneal stiffness increased after DSEK. Central corneal thickness may have less influence than corneal biomechanics on IOP measurements in eyes after DSEK. Biomechanically-corrected IOP obtained by CST seemed to be lower than other tonometry techniques in DSEK eyes, perhaps because of correction for corneal stiffness, CCT and age.

Transient Intraocular Pressure Fluctuations After Intravitreal Bevacizumab Injection in Proliferative Diabetic Retinopathy Patients: A Prospective Study

INTRODUCTION

The clinical use of intravitreal bevacizumab (IVB), a recombinant humanized monoclonal antibody that functions as an anti-vascular endothelial growth factor (anti-VEGF), has recently increased in patients with retinal ischemic diseases such as proliferative diabetic retinopathy (PDR). The short-term and long-term complications associated with this procedure have not been well established. We aimed to study the possible short-term complication of intraocular pressure (IOP) fluctuations shortly after IVB injection in patients with PDR.

MATERIALS AND METHODS

A prospective case series of diabetic patients with PDR who underwent IVB injection was performed in the Department of Ophthalmology, Medical Teaching Institution, Khyber Teaching Hospital, Peshawar, Pakistan, from November 1, 2020, to May 1, 2021. The total number of PDR patients of both sexes included in the study was 101. A slit lamp examination was performed, and IOP readings were recorded before and 30 min after IVB injection using Goldmann applanation tonometry (GAT). IBM Statistical Package for the Social Sciences version 22 for Windows was used to analyze the data. Safety of the procedure, defined as IOP ≤20 mmHg 30 min after IVB injection, was determined and stratified according to sex, age, duration of diabetes, and baseline IOP. A post-stratification chi-square test was applied, and a p-value <0.05 was taken as statistically significant.

RESULTS

In this study, 60.4% of the participants were male and 39.6% were female. The age of the patients ranged from 30 to 75 years, with a mean age of 55.66±6.37 years. The mean duration of diabetes among the participants was 7.73±2.94 years and the mean baseline IOP was 15.40±1.77 mmHg. Safety (IOP ≤20 mmHg 30 min after IVB injection) was observed in 90.1% of the patients.

CONCLUSION

IVB injections are safe for use in patients with PDR in terms of immediate IOP changes. However, patients with higher baseline IOP (>15 mmHg) are more likely to develop increased IOP post-procedure and prophylaxis may be prudent in such cases.

TFOS Lifestyle: Impact of nutrition on the ocular surface

Nutrients, required by human bodies to perform life-sustaining functions, are obtained from the diet. They are broadly classified into macronutrients (carbohydrates, lipids, and proteins), micronutrients (vitamins and minerals) and water. All nutrients serve as a source of energy, provide structural support to the body and/or regulate the chemical processes of the body. Food and drinks also consist of non-nutrients that may be beneficial (e.g., antioxidants) or harmful (e.g., dyes or preservatives added to processed foods) to the body and the ocular surface. There is also a complex interplay between systemic disorders and an individual's nutritional status. Changes in the gut microbiome may lead to alterations at the ocular surface. Poor nutrition may exacerbate select systemic conditions. Similarly, certain systemic conditions may affect the uptake, processing and distribution of nutrients by the body. These disorders may lead to deficiencies in micro- and macro-nutrients that are important in maintaining ocular surface health. Medications used to treat these conditions may also cause ocular surface changes. The prevalence of nutrition-related chronic diseases is climbing worldwide. This report sought to review the evidence supporting the impact of nutrition on the ocular surface, either directly or as a consequence of the chronic diseases that result. To address a key question, a systematic review investigated the effects of intentional food restriction on ocular surface health; of the 25 included studies, most investigated Ramadan fasting (56%), followed by bariatric surgery (16%), anorexia nervosa (16%), but none were judged to be of high quality, with no randomized-controlled trials.

Immune Fingerprint in Diabetes: Ocular Surface and Retinal Inflammation

Diabetes is a prevalent global health issue associated with significant morbidity and mortality. Diabetic retinopathy (DR) is a well-known inflammatory, neurovascular complication of diabetes and a leading cause of preventable blindness in developed countries among working-age adults. However, the ocular surface components of diabetic eyes are also at risk of damage due to uncontrolled diabetes, which is often overlooked. Inflammatory changes in the corneas of diabetic patients indicate that inflammation plays a significant role in diabetic complications, much like in DR. The eye's immune privilege restricts immune and inflammatory responses, and the cornea and retina have a complex network of innate immune cells that maintain immune homeostasis. Nevertheless, low-grade inflammation in diabetes contributes to immune dysregulation. This article aims to provide an overview and discussion of how diabetes affects the ocular immune system's main components, immune-competent cells, and inflammatory mediators. By understanding these effects, potential interventions and treatments may be developed to improve the ocular health of diabetic patients.

Analysis of Corneal Deformation in Paediatric Patients Affected by Maturity Onset Diabetes of the Young Type 2

BACKGROUND

To evaluate corneal deformation in Maturity Onset Diabetes of the Young type 2 (MODY2), paediatric subjects were analysed using a Scheimpflug-based device. The purpose of this analysis was to find new biomarkers for MODY2 disease and to gain a better understanding of the pathogenesis of the disease.

METHODS

A total of 15 patients with genetic and metabolic diagnoses of MODY2 (mean age 12.8 ± 5.66 years) and 15 age-matched healthy subjects were included. The biochemical and anthropometric data of MODY2 patients were collected from clinical records, and a complete ophthalmic check with a Pentacam HR EM-3000 Specular Microscope and Corvis ST devices was performed in both groups.

RESULTS

Highest concavity (HC) deflection length, Applanation 1 (A1) deflection amplitude, and A1 deflection area showed significantly lower values in MODY2 patients compared to healthy subjects. A significant positive correlation was observed between Body Mass Index (BMI) and HC deflection area and between waist circumference (WC) and the following parameters: maximum deformation amplitude, HC deformation amplitude, and HC deflection area. The glycosylated hemoglobin level (HbA1c) showed a significant positive correlation with Applanation 2 time and HC time.

CONCLUSIONS

The obtained results show, for the first time, differences regarding corneal distortion features in the MODY2 population compared with healthy eyes.

Central Corneal Thickness and Intraocular Pressure in Women With Gestational Diabetes Mellitus

INTRODUCTION

Pregnancy causes an increase in central corneal thickness (CCT) and a reduction in intraocular pressure (IOP), especially in the third trimester. However, there is very limited published data regarding CCT and IOP in gestational diabetes mellitus (GDM) on diet control. This study is aimed to compare the means of CCT and IOP between pregnant women with GDM on diet control, healthy pregnant women, and healthy non-pregnant women.

METHODS

This is a comparative cross-sectional study. A total of 184 women were recruited and divided into the following three groups: 61 pregnant women with GDM on diet control, 63 healthy pregnant women, and 60 healthy non-pregnant women as control. All subjects have undergone ocular examination during their 36-40 weeks of gestation. CCT measurement was done using a specular microscope and IOP measurement using a non-contact tonometer. Data from the right eye were analyzed.

RESULTS

The mean age was 32 (4.0) years in GDM on diet control, 29 (3.0) years in healthy pregnant women, and 27 (5.4) years in healthy non-pregnant women. The number of gravidas was 2.5 (0.8) in women with GDM on diet control and 2.3 (0.8) in healthy pregnant women. There was a significant difference (p<0.05) in the mean CCT in women with GDM on diet control compared to healthy pregnant and healthy non-pregnant women. The mean IOP is significantly lower in both pregnant women with GDM on diet control and healthy pregnant groups, compared to the healthy non-pregnant women group.

CONCLUSION

Women with GDM showed significantly thicker mean CCT than healthy pregnant and non-pregnant women. The mean IOP is significantly lower in both pregnant women with GDM on diet control and healthy pregnant groups, compared to the healthy non-pregnant women group.

Corneal Biomechanics Assessment with Ultra High Speed Scheimpflug Camera in Primary Open Angle Glaucoma Compared with Healthy Subjects: A meta-analysis of the Literature

PURPOSE

The aim of this meta-analysis of the literature is to provide a comprehensive analysis of the differences in Corvis ST dynamic corneal response (DCR) parameters between primary open-angle glaucoma (POAG) patients and healthy controls.

METHODS

A quantitative meta-analysis was conducted on articles published before September 10, 2021 identified by searching PubMed, EMBASE, and Web of Science. Prospective studies comparing DCR Corvis ST parameter in high tension POAG and healthy controls were included. The random-effects model was conducted. Assessment of heterogeneity was based on the calculation of I². Funnel plots evaluation and meta-regression were performed in case of detection of high heterogeneity.

RESULTS

The selection process resulted in the inclusion of six articles. Pooled analysis revealed that POAG corneas respond to mechanical stimulus with a smaller concavity, showing lower deformation amplitude (DA) (CI95% -0.991 to -0.578; p < .001; I² = 0%), higher highest concavity radius (HCR; confidence interval [CI]95% -0.01 to 0.34; p = .058; I² = 6.7%), and lower peak distance (PD; CI95% -1.06 to -0.024; p = .040; I² = 86.5%). They also show a slower loading phase, with lower highest concavity time (HCT; CI95% -0.39 to -0.02; p = .029; I² = 3.3%) and lower applanation velocity-1 (CI95% -0.641 to -0.127; p = .003; I² = 34.6%), and a faster restoration to the original form, shown by lower applanation time-2 (CI95% -1.123 to -0.544; p = .001; I² = 44.8%) compared to healthy subjects.

CONCLUSIONS

High tension POAG patients are characterized by stiffer corneas compared to healthy controls. These differences are valid also after removing the effect of age, corneal thickness, and intraocular pressure (IOP).

The alterations of corneal biomechanics in adult patients with corneal dystrophy

PURPOSE

To evaluate the changes of corneal biomechanics in granular, lattice and macular corneal dystrophy (GCD, LCD and MCD), and to assess the agreement of intraocular pressure (IOP) between Corvis ST tonometer (CST) and Goldmann applanation tonometer (GAT) and the agreement of central corneal thickness (CCT) between CST and ultrasound pachymeter (USP) in patients with corneal dystrophy.

METHODS

Fifty-nine eyes with corneal dystrophy (26 eyes with GCD, 18 eyes with LCD and 15 eyes with MCD) and 48 eyes from healthy subjects were included in this study. All subjects received ocular examination and anterior segment photography under slit-lamp microscope. Corneal biomechanical parameters were obtained using CST. IOP and CCT were obtained using GAT and USP, respectively. Mixed-effects models were fitted for group comparisons and Bland-Altman analyses were applied for assessing the agreement of IOP or CCT between devices.

RESULTS

GCD, LCD and MCD showed higher First Applanation Deformation Amplitude (A1DA) and Corvis Biomechanical Index (CBI), and a lower Stiffness Parameter at First Applanation (SPA1), compared to controls. After CCT adjustment, MCD group showed a higher A1DA compared to GCD or LCD. The IOP measured by CST demonstrated an overestimated bias to the one obtained by GAT in all groups. The CCT measured by CST and USP showed good agreement in healthy eyes but not in those with corneal dystrophy.

CONCLUSION

Corneal biomechanical alterations were observed in GCD, LCD and MCD. IOP and CCT measured by CST should be interpreted carefully in eyes with corneal dystrophy.

Biomechanical analysis of ocular diseases and its in vitro study methods

Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment.

Measurement of corneal biomechanical properties in diabetes mellitus using the Corvis ST

We sought to assess changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with those among healthy controls using Corvis ST (CST). The study group included 209 eyes from healthy control subjects and 33 eyes from diabetic subjects, respectively. Following an ophthalmological examination, measurements with CST were taken. Additionally, hemoglobin A1c and blood glucose values were collected. Results were then compared to those of the control group after adjusting for potential confounding factors, including age-, intraocular pressure (IOP)-, central corneal thickness (CCT)-, spherical equivalent (SE)- and axial length (AL). After adjusting for potential confounding factors, including the age, IOP, CCT, SE, and AL, patients with DM presented significantly lower whole-eye movement (WEM) (ms) values than patients without DM (21.71 ± 0.84 vs. 22.15 ± 0.64 ms; P < .001). There was a significant and negative correlation between WEM (ms) and hemoglobin A1c in DM patients (r = -0.733; P = .001). In univariate and multivariate general linear mixed model (GLMM) analyses, IOP (P < .001 and P < .001, respectively) and the presence of DM (P = .001 and P < .001, respectively) significantly affected WEM (ms). In DM, significant changes in corneal biomechanical properties were detectable. The DM group showed significantly less deformable cornea and sclera than did the normal controls, even after adjusting for age, IOP, CCT, SE, and AL. These findings may cause misinterpretation of IOP measurements in diabetic patients. Therefore, the measurement of corneal biomechanics should be taken into consideration in clinical practice.

The short-term effects of wearing swimming goggles on corneal biomechanics

PURPOSE

This study aimed to assess the impact of wearing swimming goggles (SG) on corneal biomechanics.

METHODS

Corneal deformation response, central corneal thickness (CCT), intraocular pressure (IOP) and biomechanically corrected intraocular pressure (bIOP) were measured with the Corvis system (Oculus Optikgeräte GmbH, Wetzlar, Germany) in thirty-one healthy young adults while wearing a drilled SG. All measurements were obtained before, at 30 s, 2 min, 3.5 min and 5 min of wearing SG, just after SG removal and after 2 min of SG removal.

RESULTS

The corneal biomechanics is sensitive to SG wear, observing lower corneal deformability during SG use. Specifically, wearing SG caused an increase in the time and length of the first applanation and radius curvature at the highest concavity, as well as a decrease and in the velocity of the first applanation and time and deformation amplitude of the second applanation (p < 0.001 in all cases). After SG removal, corneal biomechanical parameters showed a rebound-effect, obtaining a higher corneal deformability in comparison with baseline reading (p-corrected < 0.05 in all cases). Additionally, IOP and bIOP significantly increased while wearing SG (p < 0.001 in both cases), whereas CCT remained stable (p = 0.850).

CONCLUSIONS

Wearing SG modifies the biomechanical properties of the cornea, with reduced corneal deformability during SG wear. The outcomes of this study should be taken into consideration when making clinical decisions in subjects at high risk of developing corneal ectasias or glaucoma, as well as in the post-surgical management of these ocular conditions.

Measurement of In Vivo Biomechanical Changes Attributable to Epithelial Removal in Keratoconus Using a Noncontact Tonometer

PURPOSE

To compare the biomechanical properties of the cornea after epithelial removal in eyes with keratoconus undergoing corneal cross-linking.

METHODS

Prospective interventional case series at a university hospital tertiary referral center. Corneal biomechanical properties were measured in patients with keratoconus undergoing corneal cross-linking, immediately before and after epithelial debridement by using a dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer.

RESULTS

The study comprised 45 eyes of 45 patients with a mean age of 19.6 ± 4.9 years (range 14-34). The cornea was found to be 23.7 ± 15.7 μm thinner after epithelial removal (P < 0.01). Corneal stiffness was reduced after epithelial removal as demonstrated by a significant decrease of parameters such as stiffness parameter A1 (12.31, P < 0.01), stiffness parameter-highest concavity (2.25, P < 0.01), A1 length (0.13 mm, P = 0.04), highest concavity radius of curvature (0.26 mm, P = 0.01), highest concavity time (0.22 ms, P = 0.04) and an increase in A1 velocity (-0.01 m/s, P = 0.01), A1 deformation amplitude (-0.03 mm, P ≤ 0.01), A1 deflection length (-0.32 mm, P < 0.01), A2 deformation amplitude (-0.03 mm, P = 0.01), and A2 deflection length (-1.00 mm, P < 0.01). There were no significant differences in biomechanical intraocular pressure (0.15 mm Hg, P = 0.78), deformation amplitude (0.03, P = 0.54), maximum inverse radius (-0.01 mm, P = 0.57), and whole eye movement length (-0.02 mm, P = 0.12).

CONCLUSIONS

Dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer offers an alternative method for in vivo measurements of the epithelial layer's contribution to corneal biomechanical properties. Our results suggest that corneal epithelium may play a more significant role in corneal biomechanical properties in patients with keratoconus than previously described.

Factors Influencing Corneal Biomechanics in Diabetes Mellitus

PURPOSE

Diabetes mellitus (DM) induces changes in corneal biomechanical properties. The influence of disease-specific factors was evaluated, and a novel DM index was created.

METHODS

Eighty-one patients with DM and 75 healthy subjects were matched according to age, intraocular pressure, and central corneal thickness. Information on the disease was collected, and measurements with the Ocular Response Analyzer and the Corvis ST were taken. Results were compared between the groups, and the influence of disease-specific factors was evaluated. From dynamic corneal response parameters, a DM index was calculated.

RESULTS

In DM, corneal hysteresis was higher than in healthy subjects (10.5 ± 1.9 vs. 9.7 ± 1.9 mm Hg, P = 0.008). In addition, dynamic corneal response parameters showed significant differences. Among others, highest concavity (HC) (17.212 ± 0.444 vs. 16.632 ± 0.794 ms, P < 0.001) and A2 time (21.85 ± 0.459 vs. 21.674 ± 0.447 ms, P = 0.017) as well as A1 (0.108 ± 0.008 vs. 0.104 ± 0.011 mm, P = 0.019) and A2 deflection amplitudes (0.127 ± 0.014 vs. 0.119 ± 0.014 mm, P < 0.001) were increased in DM. In DM type 1, HC deformation amplitude (1.14 ± 0.19 vs. 1.095 ± 0.114 mm, P = 0.035) was higher than in type 2. The time of deflection amplitude max correlated with the severity of retinopathy (R = 0.254, P= 0.023). In case of diabetic maculopathy, A1 velocity (0.155 ± 0.018 vs. 0.144 ± 0.019 ms, P = 0.043) and A2 time (22.052 ± 0.395 vs. 21.79 ± 0.46 ms, P = 0.04) were increased. Deformation amplitude max (R = 0.297, P = 0.024), HC time (R = 0.26, P = 0.049), HC deformation amplitude (R = 0.297, P = 0.024), and A2 deformation amplitude (R = 0.276, P = 0.036) were associated to disease duration. The DM index revealed a sensitivity of 0.773 and a specificity of 0.808 (area under the curve of receiver operating characteristic = 0.833).

CONCLUSIONS

In DM, changes in corneal biomechanics were correlated with disease-specific factors. The DM index achieved reliable sensitivity and specificity values.

Corneal Biomechanical Properties in Varying Severities of Myopia

Purpose: To investigate corneal biomechanical response parameters in varying degrees of myopia and their correlation with corneal geometrical parameters and axial length.

Methods: In this prospective cross-sectional study, 172 eyes of 172 subjects, the severity degree of myopia was categorized into mild, moderate, severe, and extreme myopia. Cycloplegic refraction, corneal tomography using Pentacam HR, corneal biomechanical assessment using Corvis ST and Ocular Response Analyser (ORA), and ocular biometry using IOLMaster 700 were performed for all subjects. A general linear model was used to compare biomechanical parameters in various degrees of myopia, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered as covariates. Multiple linear regression was used to investigate the relationship between corneal biomechanical parameters with spherical equivalent (SE), axial length (AXL), bIOP, mean keratometry (Mean KR), and CCT.

Results: Corneal biomechanical parameters assessed by Corvis ST that showed significant differences among the groups were second applanation length (AL2, p = 0.035), highest concavity radius (HCR, p < 0.001), deformation amplitude (DA, p < 0.001), peak distance (PD, p = 0.022), integrated inverse radius (IR, p < 0.001) and DA ratio (DAR, p = 0.004), while there were no significant differences in the means of pressure-derived parameters of ORA between groups. Multiple regression analysis showed all parameters of Corvis ST have significant relationships with level of myopia (SE, AXL, Mean KR), except AL1 and AL2. Significant biomechanical parameters showed progressive reduction in corneal stiffness with increasing myopia (either with greater negative SE or greater AXL), independent of IOP and CCT. Also, corneal hysteresis (CH) or ability to dissipate energy from the ORA decreased with increasing level of myopia.

Conclusions: Dynamic corneal response assessed by Corvis ST shows evidence of biomechanical changes consistent with decreasing stiffness with increasing levels of myopia in multiple parameters. The strongest correlations were with highest concavity parameters where the sclera influence is maximal.

Intracorneal Stromal Ring Can Affect the Biomechanics of Ectatic Cornea

Purpose

The biomechanical properties of ecstatic cornea undergo changes. This study evaluates the biomechanical changes of ecstatic cornea after implantation of two types of intracorneal stromal ring (ICR).

Methods

For doing this prospective cross-sectional study, 32 patients with keratoconus (KCN) were randomly divided into two 16-member groups (group I: MyoRing, group II: KeraRing). The main inclusion criteria were transparent cornea with no scar in the central part, corneal thickness >450 µ in the incision region, keratometry within 48–52 diopters, and progressive course of corneal thinning. Biomechanics of the cornea was evaluated by “ORA” and “Corvis” devices. All of the data were recorded and analyzed before implantation of the rings and 6 months thereafter.

Results

The mean ages of patients of groups I and II were 26 ± 6.55 and 33.86 ± 8.5, respectively. The postoperative change of sphere refraction was significant in both groups. However, reduction in the astigmatism was significant only in group I. In addition, the change of flat meridian keratometry (Kf) was significant before and after ring implantation in group I, unlike group II. The changes in CH and CRF parameters (ORA) were not significant in either group before and after the operation. Besides, only HRC parameter (Corvis) decreased significantly in both groups before and after the operation.

Conclusion

Both MyoRing and KeraRings have positive effects on the biomechanics of cornea at least during the first year after implantation. Comparison of these two types of ICR did not show significant differences in Corvis and ORA parameters.

Evaluation of biomechanically corrected intraocular pressure using Corvis ST and comparison of the Corvis ST, noncontact tonometer, and Goldmann applanation tonometer in patients with glaucoma

Purpose

The aim of the study was to investigate the effects of various anatomical structures on intraocular pressure (IOP) measurements obtained by the Corneal Visualization Scheimpflug Technology (Corvis ST), Goldmann applanation tonometer (GAT), and noncontact tonometer (NCT), as well as to assess the interchangeability among the four types of IOP measurement: IOP-GAT, IOP-NCT, IOP-Corvis, and biomechanically corrected IOP (bIOP-Corvis), with a particular focus on bIOP-Corvis.

Materials and methods

We included 71 patients with primary open-angle glaucoma and assessed their IOP measurements obtained with the GAT, NCT, and Corvis ST using a repeated measures ANOVA, a paired t-test with Bonferroni correction, stepwise multiple regression analyses and Bland–Altman plots.

Results

IOP-GAT showed the highest values (13.5 ± 2.1 mmHg [mean ± standard deviation]), followed by IOP-NCT (13.2 ± 2.7 mmHg), IOP-Corvis (10.6 ± 2.8 mmHg), and bIOP-Corvis (10.0 ± 2.3 mmHg). With exceptions of bIOP-Corvis and IOP-GAT, all IOP variations were explained by regression coefficients involving the central corneal thickness. Bland–Altman plots showed a mean difference between IOP-GAT and the other IOP measurements (IOP-Corvis, bIOP-Corvis, and IOP-NCT), which were -2.90, -3.48, and -0.29 mmHg, respectively. The widths of the 95% limits of agreement between all pairs of IOP measurements were greater than 3 mmHg.

Conclusion

IOP values obtained with the Corvis ST, NCT, and GAT were not interchangeable. The bIOP-Corvis measurement corrected for the ocular structure.

Diabetic keratopathy: Insights and challenges

Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.

Changes in corneal biomechanics in patients with diabetes mellitus: a systematic review and meta-analysis

AIMS

To determine the changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with controls.

METHODS

Pertinent studies were identified by comprehensively search of PubMed, Embase, the Web of Science, the Cochrane Library, Scopus, the China National Knowledge Infrastructure and the Chinese biomedical disc (CBM) databases. Pooling analyses by random models using the D-L method were performed for corneal hysteresis (CH), the corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOPg).

RESULTS

A total of 15 studies were included in the final analysis, involving 1506 eyes in the diabetic group and 2190 eyes in the control group. The diabetic group had significantly higher CH, CRF, IOPg and IOPcc values than the control group. The pooled mean differences were 1.34 mmHg (95% confidence interval [CI] 0.60-2.08 mmHg, P < 0.001) for IOPg and 0.85 mmHg (95% CI 0.18-1.51 mmHg, P = 0.013) for IOPcc, 0.38 mmHg (95% CI 0.01-0.75, P = 0.047) for CH and 0.63 mmHg (95% CI 0.27-0.98, P = 0.001) for the CRF. Sensitivity analyses using the leave-one-out method showed a consistent significant difference between the groups (all P < 0.001).

CONCLUSIONS

Corneal biomechanics changed in the patients with DM. High CH, CRF, IOPcc and IOPg values may be associated factors for diabetes mellitus. Future studies are warranted to clarify the underlying mechanisms and explore the relationship between corneal biomechanics, glaucoma and diabetes mellitus.

REGISTRATION

PROSPERO registration No CRD4201705465.

Corneal Biomechanical Changes After Uneventful Phacoemulsification in Patients With Type 2 Diabetes Mellitus and Patients Without Diabetes

PURPOSE

To compare corneal biomechanical changes after uneventful phacoemulsification cataract surgery between type 2 diabetic (DM) and nondiabetic patients.

METHODS

Forty-four diabetic (44 eyes) and 44 (44 eyes) age and sex-matched non-DM controls with age-related cataract were enrolled in this prospective observational study. Corneal hysteresis (CH), corneal resistance factor (CRF), and corneal-compensated intraocular pressure (IOPcc) were evaluated by using the ocular response analyzer; central corneal thickness was recorded by using the Pentacam HR. Patients were evaluated preoperatively and 1 and 6 months after surgery.

RESULTS

In the DM group, CH was observed to be significantly lower than preoperative value (9.8 ± 1.5 mm Hg) at 1 month (9.4 ± 1.2 mm Hg, P = 0.040), but not at the 6-month follow-up (9.6 ± 1.6 mm Hg, P = 0.437),whereas it did not change significantly in the non-DM group (preoperative 9.8 ± 1.3 mm Hg vs. 1 month 9.6 ± 1.1 mm Hg vs. 6 months 10.1 ± 1.1 mm Hg, P > 0.05). CRF was significantly lower than the preoperative values at 1 and 6 months in both groups (P ≤ 0.001). Postoperative CH change was significantly associated with preoperative CH (P < 0.001), preoperative IOPcc (P = 0.004), and IOPcc change (P < 0.001), whereas CRF change was only correlated with preoperative CRF (P < 0.001). There was a significant postoperative IOPcc reduction 6 months after surgery (P < 0.001) in both DM and non-DM groups; however, central corneal thickness was not found to significantly change in the postoperative period (P > 0.05).

CONCLUSIONS

This study showed that phacoemulsification causes a significant and persistent decrease in intraocular pressure and CRF in both groups, whereas CH recovered to preoperative values, although more slowly in patients with diabetes.

Intraocular pressure measurements in diabetes mellitus

PURPOSE

To investigate the impact of diabetes mellitus-induced changes on intraocular pressure measurements using Goldmann applanation tonometry, Ocular Response Analyzer, and Corvis ST.

METHODS

Measurements were done using Goldmann applanation tonometry, Ocular Response Analyzer, and Corvis ST in 69 diabetic patients. Biomechanical-corrected intraocular pressure values by Ocular Response Analyzer (IOPcc) and Corvis ST (bIOP) were used. In addition, biometry and tomography were performed and information on diabetes mellitus specific factors was collected. Results were compared to an age-matched group of 68 healthy subjects.

RESULTS

In diabetes mellitus, Goldmann applanation tonometry intraocular pressure (P = 0.193) and central corneal thickness (P = 0.184) were slightly increased. Also, IOPcc (P = 0.075) and bIOP (P = 0.542) showed no significant group difference. In both groups, IOPcc was higher than Goldmann applanation tonometry intraocular pressure (P = 0.002, P < 0.001), while bIOP was nearly equal to Goldmann applanation tonometry intraocular pressure (P = 0.795, P = 0.323). Central corneal thickness showed a tendency to higher values in poorly controlled than in controlled diabetes mellitus (P = 0.059). Goldmann applanation tonometry intraocular pressure correlated to central corneal thickness, while IOPcc and bIOP were independent from central corneal thickness in both groups. All intraocular pressure values showed significant associations to corneal biomechanical parameters. Only in diabetes mellitus, bIOP was correlated to Pachy slope (P = 0.023).

CONCLUSION

In diabetes mellitus, Goldmann applanation tonometry intraocular pressure was slightly, but not significantly, increased, which might be caused by a higher central corneal thickness and changes in corneal biomechanical properties. However, intraocular pressure values measured by Ocular Response Analyzer and Corvis ST were not significantly different between diabetes mellitus patients and healthy subjects. The bIOP showed a higher agreement with Goldmann applanation tonometry than IOPcc and was independent from central corneal thickness.

Mechanisms of Collagen Crosslinking in Diabetes and Keratoconus

Collagen crosslinking provides the mechanical strength required for physiological maintenance of the extracellular matrix in most tissues in the human body, including the cornea. Aging and diabetes mellitus (DM) are processes that are both associated with increased collagen crosslinking that leads to increased corneal rigidity. By contrast, keratoconus (KC) is a corneal thinning disease associated with decreased mechanical stiffness leading to ectasia of the central cornea. Studies have suggested that crosslinking mediated by reactive advanced glycation end products during DM may protect the cornea from KC development. Parallel to this hypothesis, riboflavin-mediated photoreactive corneal crosslinking has been proposed as a therapeutic option to halt the progression of corneal thinning by inducing intra- and intermolecular crosslink formation within the collagen fibrils of the stroma, leading to stabilization of the disease. Here, we review the pathobiology of DM and KC in the context of corneal structure, the epidemiology behind the inverse correlation of DM and KC development, and the chemical mechanisms of lysyl oxidase-mediated crosslinking, advanced glycation end product-mediated crosslinking, and photoreactive riboflavin-mediated corneal crosslinking. The goal of this review is to define the biological and chemical pathways important in physiological and pathological processes related to collagen crosslinking in DM and KC.

Genetic Correlations Between Diabetes and Glaucoma: An Analysis of Continuous and Dichotomous Phenotypes

PURPOSE

A genetic correlation is the proportion of phenotypic variance between traits that is shared on a genetic basis. Here we explore genetic correlations between diabetes- and glaucoma-related traits.

DESIGN

Cross-sectional study.

METHODS

We assembled genome-wide association study summary statistics from European-derived participants regarding diabetes-related traits like fasting blood sugar (FBS) and type 2 diabetes (T2D) and glaucoma-related traits (intraocular pressure [IOP], central corneal thickness [CCT], corneal hysteresis [CH], corneal resistance factor [CRF], cup-to-disc ratio [CDR], and primary open-angle glaucoma [POAG]). We included data from the National Eye Institute Glaucoma Human Genetics Collaboration Heritable Overall Operational Database, the UK Biobank, and the International Glaucoma Genetics Consortium. We calculated genetic correlation (rg) between traits using linkage disequilibrium score regression. We also calculated genetic correlations between IOP, CCT, and select diabetes-related traits based on individual level phenotype data in 2 Northern European population-based samples using pedigree information and Sequential Oligogenic Linkage Analysis Routines.

RESULTS

Overall, there was little rg between diabetes- and glaucoma-related traits. Specifically, we found a nonsignificant negative correlation between T2D and POAG (rg = -0.14; P = .16). Using Sequential Oligogenic Linkage Analysis Routines, the genetic correlations between measured IOP, CCT, FBS, fasting insulin, and hemoglobin A1c were null. In contrast, genetic correlations between IOP and POAG (rg ≥ 0.45; P ≤ 3.0 × 10-4) and between CDR and POAG were high (rg = 0.57; P = 2.8 × 10-10). However, genetic correlations between corneal properties (CCT, CRF, and CH) and POAG were low (rg range -0.18 to 0.11) and nonsignificant (P ≥ .07).

CONCLUSION

These analyses suggest that there is limited genetic correlation between diabetes- and glaucoma-related traits.

An Update on Corneal Biomechanics and Architecture in Diabetes

In the last decade, we have witnessed substantial progress in our understanding of corneal biomechanics and architecture. It is well known that diabetes is a systemic metabolic disease that causes chronic progressive damage in the main organs of the human body, including the eyeball. Although the main and most widely recognized ocular effect of diabetes is on the retina, the structure of the cornea (the outermost and transparent tissue of the eye) can also be affected by the poor glycemic control characterizing diabetes. The different corneal structures (epithelium, stroma, and endothelium) are affected by specific complications of diabetes. The development of new noninvasive diagnostic technologies has provided a better understanding of corneal tissue modifications. The objective of this review is to describe the advances in the knowledge of the corneal alterations that diabetes can induce.

Structural and Biomechanical Corneal Differences between Type 2 Diabetic and Nondiabetic Patients

Purpose

To analyze and compare corneal structural and biomechanical properties, characterized by corneal hysteresis (CH) and resistance factor (CRF), between patients with and without type 2 diabetes mellitus (DM), and determine the main ocular variables that influence them.

Methods

Sixty diabetic and 48 age- and sex-matched non-DM patients were enrolled in this cross-sectional study. The DM group was analyzed according to DM duration (<or ≥ 10 years), HbA1c levels (<or ≥ 7%), and presence of retinopathy. CH and CRF were evaluated using the Ocular Response Analyzer® (ORA). Central corneal thickness (CCT) was determined by Scheimpflug tomography (Pentacam® HR). Intraocular pressure was obtained with ORA (IOPcc) and Goldmann applanation tonometry (IOP-GAT). Univariate and multivariate linear regression analyses were performed to evaluate the relationship between demographical, clinical, and ocular variables with the biomechanical properties.

Results

There were no statistically significant differences in the CH and the CRF between DM and non-DM groups (p=0.637 and p=0.439, respectively). Also, there was no statistical difference between groups for the CCT, IOPcc, or IOP-GAT. Multivariate linear regression analysis showed that CH was positively associated with CCT (p < 0.001) and negatively associated with IOPcc (p < 0.001), while CRF was positively associated with CCT (p < 0.001) and IOPcc (p=0.014).

Conclusion

The CCT and IOPcc were found to be the main parameters that affect corneal biomechanical properties both in diabetics and controls. In this study, there was no significant effect of DM type 2 on corneal biomechanics.

Biomechanical changes in the cornea following cataract surgery: A prospective assessment with the Corneal Visualisation Scheimpflug Technology

IMPORTANCE

Intraocular pressure (IOP) is often reduced following cataract surgery. Postoperative changes in corneal stiffness are likely to be at least partly responsible for any reduction in IOP measured with applanation tonometry.

BACKGROUND

To determine the effect of cataract surgery and corneal incision size on corneal biomechanics.

DESIGN

Prospective randomized trial.

PARTICIPANTS

One hundred prospectively enrolled patients qualifying for cataract surgery.

METHODS

Participants were randomized to clear corneal incisions with a 2.20 or 2.85 mm keratome. Corneal Visualisation Scheimpflug Technology (Corvis-ST) tonometry and dynamic corneal response measurements were obtained preoperatively, and 3 mo postoperatively. Multiple regression analysis was completed using R software.

MAIN OUTCOME MEASURES

Corvis-ST biomechanical parameters.

RESULTS

Ninety-three eyes of 93 patients were included in the final analysis. Mean Corvis-ST biomechanically corrected IOP decreased by 3.63 mmHg postoperatively (95% confidence interval = 2.97-4.35, P ≤ 0.01), and central pachymetry increased by 6.96 μm (4.33-9.59, P ≤ 0.01). Independent of IOP and pachymetry changes, mean (±SE) corneal first applanation stiffness parameter reduced by 9.761 ± 3.729 (P = 0.01) postoperatively. First applanation velocity increased by 0.007 ± 0.002 ms, second applanation velocity increased by 0.012 ± 0.004 ms (P ≤ 0.01), the first applanation deformation amplitude increased by 0.008 ± 0.002 mm (P ≤ 0.01) and the deflection amplitude at highest concavity increased by 0.030 ± 0.069 (P ≤ 0.01). There were no significant differences between different incision size groups.

CONCLUSIONS AND RELEVANCE

Corneal stiffness is reduced 3 mo following cataract surgery and is associated with falsely low IOP measurements. This finding may be important for glaucoma patients and in particular when assessing the effectivity of minimally invasive glaucoma surgery devices.

Corneal Vibrations during Intraocular Pressure Measurement with an Air-Puff Method

Introduction

The paper presents a commentary on the method of analysis of corneal vibrations occurring during eye pressure measurements with air-puff tonometers, for example, Corvis. The presented definition and measurement method allow for the analysis of image sequences of eye responses—cornea deformation. In particular, the outer corneal contour and sclera fragments are analysed, and 3D reconstruction is performed.

Methods

On this basis, well-known parameters such as eyeball reaction or corneal response are determined. The next steps of analysis allow for automatic and reproducible separation of four different corneal vibrations. These vibrations are associated with (1) the location of the maximum of cornea deformation; (2) the cutoff area measured in relation to the cornea in a steady state; (3) the maximum of peaks occurring between applanations; and (4) the other characteristic points of the corneal contour.

Results

The results obtained enable (1) automatic determination of the amplitude of vibrations; (2) determination of the frequency of vibrations; and (3) determination of the correlation between the selected types of vibrations.

Conclusions

These are diagnostic features that can be directly applied clinically for new and archived data.

Correlation of the anterior ocular segment biometry with HbA1c level in type 2 diabetes mellitus patients

Objectives

To compare the anterior ocular segment biometry among Type 2 diabetes mellitus (DM) with no diabetic retinopathy (DR) and non-proliferative diabetic retinopathy (NPDR), and to evaluate the correlation of anterior ocular segment biometry with HbA1c level.

Methods

A cross-sectional study was conducted in Hospital Universiti Sains Malaysia, Kelantan from November 2013 till May 2016 among Type 2 DM patients (DM with no DR and DM with NPDR). The patients were evaluated for anterior ocular segment biometry [central corneal thickness (CCT), anterior chamber width (ACW), angle opening distance (AOD) and anterior chamber angle (ACA)] by using Anterior Segment Optical Coherence Tomography (AS-OCT). Three ml venous blood was taken for the measurement of HbA1c.

Results

A total of 150 patients were included in this study (DM with no DR: 50 patients, DM with NPDR: 50 patients, non DM: 50 patients as a control group). The mean CCT and ACW showed significant difference among the three groups (p < 0.001 and p = 0.015 respectively). Based on post hoc result, there were significant mean difference of CCT between non DM and DM with NPDR (mean difference 36.14 μm, p < 0.001) and also between non DM and DM with no DR (mean difference 31.48 μm, p = 0.003). The ACW was significantly narrower in DM with NPDR (11.39 mm SD 0.62) compared to DM with no DR (11.76 mm SD 0.53) (p = 0.012). There were no significant correlation between HbA1c and all the anterior ocular segment biometry.

Conclusion

Diabetic patients have significantly thicker CCT regardless of retinopathy status whereas ACW was significantly narrower in DM with NPDR group compared to DM with no DR. There was no significant correlations between HbA1c and all anterior ocular segment biometry in diabetic patients regardless of DR status.

Measurement repeatability of the dynamic Scheimpflug analyzer

PURPOSE

To evaluate the repeatability of corneal deformation parameters measured using a dynamic Scheimpflug analyzer and the impact of baseline clinical factors on the repeatability of each parameter.

STUDY DESIGN

Retrospective, cross-sectional study.

METHODS

Forty-eight eyes (48 healthy subjects; mean age, 49.0 ± 19.5 years) underwent repeated examinations with the Scheimpflug analyzer to evaluate the test-retest variability. The intraclass correlation coefficient (ICC) and repeatability coefficient as indicators of variability were computed for 35 parameters measured with the Scheimpflug analyzer. The associations between the magnitude of the test-retest variability and baseline factors, such as age, axial length (AL), intraocular pressure (IOP), and central corneal thickness (CCT), were analyzed.

RESULTS

The test-retest repeatability was excellent for 22 (62.9%) of 35 parameters (ICC ≥ 0.75), good for seven (20%), (ICC ≥ 0.6), fair for four (11.4%), (ICC ≥ 0.4), and poor for two (5.7%) parameters (ICC < 0.4). Age was associated positively with the magnitude of variability in 13 (37.1%) parameters; measurement variability was affected significantly by AL (5 parameters, 14.3%) and CCT (7 parameters, 20%) but, except for one parameter not by IOP.

CONCLUSION

Most parameters of the dynamic Scheimpflug analyzer showed favorable measurement reliability in healthy subjects. However, six parameters showed poor-to-fair repeatability. Age, AL, and CCT significantly affected the repeatability of several parameters. These results should be considered when clinicians use this device in clinical practice.

Effects of diabetes mellitus on biomechanical properties of the rabbit cornea

To investigate the effects of diabetes on the biomechanical behavior of cornea in alloxan-induced diabetic rabbits. Diabetes mellitus (DM) was induced in 20 rabbits using alloxan, while another 20 age- and weight-matched non-diabetic rabbits served as controls. Eyes were enucleated after 8 weeks of inducing diabetes and the whole cornea was removed with a 3 mm wide scleral ring and tested under inflation conditions with an internal pressure range of 2.0-30.0 mmHg to determine their stress-strain behavior using an inverse analysis process. The blood glucose level (BG), advanced glycosylation end products (AGEs), central corneal thickness (CCT) and intraocular pressure (IOP) increased significantly in the DM group. There were statistically significant correlations between BG and AGEs (r = 0.768, p = 0.00), and between AGEs and CCT variation upon induction of DM (r = 0.594, p = 0.00). The tangent modulus (Et) of the cornea at four stress levels (1-4 kPa, equivalent to approximately IOP of 7.5, 15, 22.5 and 30 mmHg, respectively) was significantly higher in diabetic rabbits than in the control group (p < 0.05). Further, Et at stress of 2 kPa (which corresponded to the average IOP for the control group) was significantly correlated with BG (r = 0.378, p < 0.05), AGEs (r = 0.496, p < 0.05) and CCT variation upon induction of DM (r = 0.439, p < 0.05). IOP, as measured by contact tonometry, was also significantly correlated with both CCT (r = 0.315, p < 0.05) and Et at 2 kPa (r = 0.329, p < 0.05), and even after correcting for the effects of CCT and Et, IOP still significantly increased with both AGEs (r = 0.772, p = 0.00) and BG (r = 0.762, p = 0.00). The cornea of diabetic rabbits showed a significant increase in mechanical stiffness as evidenced by increases in corneal thickness and tangent modulus. The Et increase may be explained by a non-enzymatic cross-linking of collagen fibrils mediated by AGEs due to the high blood glucose levels in diabetes. The study also found significant IOP increases with higher blood glucose level even after controlling the effects of both corneal thickness and tangent modulus.

A systematic review on the impact of diabetes mellitus on the ocular surface

Diabetes mellitus is associated with extensive morbidity and mortality in any human community. It is well understood that the burden of diabetes is attributed to chronic progressive damage in major end-organs, but it is underappreciated that the most superficial and transparent organ affected by diabetes is the cornea. Different corneal components (epithelium, nerves, immune cells and endothelium) underpin specific systemic complications of diabetes. Just as diabetic retinopathy is a marker of more generalized microvascular disease, corneal nerve changes can predict peripheral and autonomic neuropathy, providing a window of opportunity for early treatment. In addition, alterations of immune cells in corneas suggest an inflammatory component in diabetic complications. Furthermore, impaired corneal epithelial wound healing may also imply more widespread disease. The non-invasiveness and improvement in imaging technology facilitates the emergence of new screening tools. Systemic control of diabetes can improve ocular surface health, possibly aided by anti-inflammatory and vasoprotective agents.

Cataract surgery causes biomechanical alterations to the eye detectable by Corvis ST tonometry

PURPOSE

Modern cataract surgery is generally considered to bring about modest and sustained intraocular pressure (IOP) reduction. However, the pathophysiological mechanism for this remains unclear. Moreover, a change in ocular biomechanical properties after surgery can affect the measurement of IOP. The aim of the study is to investigate ocular biomechanics, before and following cataract surgery, using Corvis ST tonometry (CST).

PATIENTS AND METHODS

Fifty-nine eyes of 59 patients with cataract were analyzed. IOP with Goldmann applanation tonometry (IOP-G), axial length, corneal curvature and CST parameters were measured before cataract surgery and, up to 3 months, following surgery. Since CST parameters are closely related to IOP-G, linear modeling was carried out to investigate whether there was a change in CST measurements following cataract surgery, adjusted for a change in IOP-G.

RESULTS

IOP-G significantly decreased after surgery (mean±standard deviation: 11.8±3.1 mmHg) compared to pre-surgery (15.2±4.3 mmHg, P<0.001). Peak distance (the distance between the two surrounding peaks of the cornea at the highest concavity), maximum deformation amplitude (the movement of the corneal apex from the start of deformation to the highest concavity) and A1/A2 velocity (the corneal velocity during inward or outward movement) significantly increased after cataract surgery (P<0.05) while radius (the central curvature radius at the highest concavity) was significantly smaller following cataract surgery (P<0.05). Linear modeling supported many of these findings, suggesting that peak distance, maximum deformation amplitude and A2 velocity were increased, whereas A2 deformation amplitude and highest concavity time were decreased (after adjustment for IOP change), following cataract surgery.

CONCLUSION

Corneal biomechanical properties, as measured with CST, were observed to change significantly following cataract surgery.

TRIAL REGISTRATION

Japan Clinical Trials Registry UMIN000014370.

In Vivo Corneal Biomechanical Properties with Corneal Visualization Scheimpflug Technology in Chinese Population

Purpose. To determine the repeatability of recalculated corneal visualization Scheimpflug technology (CorVis ST) parameters and to study the variation of biomechanical properties and their association with demographic and ocular characteristics. Methods. A total of 783 healthy subjects were included in this study. Comprehensive ophthalmological examinations were conducted. The repeatability of the recalculated biomechanical parameters with 90 subjects was assessed by the coefficient of variation (CV) and intraclass correlation coefficient (ICC). Univariate and multivariate linear regression models were used to identify demographic and ocular factors. Results. The repeatability of the central corneal thickness (CCT), deformation amplitude (DA), and first/second applanation time (A1/A2-time) exhibited excellent repeatability (CV% ≤ 3.312% and ICC ≥ 0.929 for all measurements). The velocity in/out (V_in/out), highest concavity- (HC-) radius, peak distance (PD), and DA showed a normal distribution. Univariate linear regression showed a statistically significant correlation between V_in, V_out, DA, PD, and HC-radius and IOP, CCT, and corneal volume, respectively. Multivariate analysis showed that IOP and CCT were negatively correlated with V_in, DA, and PD, while there was a positive correlation between V_out and HC-radius. Conclusion. The ICCs of the recalculated parameters, CCT, DA, A1-time, and A2-time, exhibited excellent repeatability. IOP, CCT, and corneal volume significantly influenced the biomechanical properties of the eye.

Corneal biomechanical characteristics measured by the CorVis Scheimpflug technology in eyes with primary open-angle glaucoma and normal eyes

PURPOSE

To evaluate the biomechanical properties of the cornea using Corneal Visualization Scheimpflug Technology (CorVis ST, Oculus) in eyes with primary open-angle glaucoma (POAG) and normal control eyes.

METHODS

A comparative cross-sectional study that included 42 patients with POAG and 60 normal control subjects matched for intraocular pressure (IOP) and central corneal thickness (CCT). IOP was measured with a Goldmann applanation tonometer (GAT). Corneal tomography and biomechanical parameters were measured with Pentacam (Oculus) and CorVis ST, respectively. Corneal biomechanical properties were compared between groups, and the associations between corneal biomechanical parameters and ocular characteristics were evaluated. Receiver operating characteristic (ROC) curves were used to establish a cut-off value for the biomechanical parameters.

RESULTS

The following parameters of the CorVis ST showed a significant difference between eyes with POAG and normal eyes: first applanation velocity (Vin ), second applanation time (A-time2 ), peak distance (PD) and deformation amplitude (DA). In the univariate analysis, DA was negatively correlated with IOP in both groups. For all biomechanical parameters, the areas under the ROC curve were <0.80 and thus did not reach a good level of predictive accuracy for detecting POAG.

CONCLUSION

CorVis ST offers an alternative method for measuring corneal biomechanical properties. Eyes with POAG exhibit a faster Vin , longer A-time2 , lower DA and longer PD than do IOP- and CCT-matched normal control eyes. The biomechanical parameters of the CorVis ST cannot readily be used for diagnosis of POAG in the individual patient.

In vivo human corneal deformation analysis with a Scheimpflug camera, a critical review

Corneal morphological analysis has greatly improved in recent years, providing physicians with new and reliable parameters to study. Moreover, today corneal functional too is a routine analysis, thanks to biomechanical evaluation allowed by an ocular response analyzer (Reichert Ophthalmic Instrument, Depew, NY, USA). Corvis ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany), that relies on the ultrahigh speed Scheimpflug camera, is a new device providing corneal deformation parameters measured ny scanning the cornea response to an air puff; it is an instrument able to measure intraocular pressure too. This device could open up a whole new prospective in screening, detecting and managing corneal diseases, intraocular pressure measurement and in evaluating surgical procedures involving the cornea. This paper provides a comprehensive explanation of Corvis ST measurement principles and parameters and a literature review of scientific studies.

Increased Intraocular Pressure and Hyperglycemic Level in Diabetic Patients

Purpose

To determine whether hyperglycemic levels as determined from high hemoglobin A1c (HbA1c) levels influence intraocular pressure (IOP) in patients with non-proliferative diabetic retinopathy (NPDR).

Methods

A retrospective chart review was performed on subjects with a diagnosis of NPDR and a corresponding HbA1c level measured within 90 days before or after an IOP measurement over a two-year period. Exclusion criteria included a diagnosis of glaucoma or treatment with IOP lowering medications or oral or topical steroids.

Results

Using 14.5mmHg as a baseline mean value for IOP, 42 subjects had an IOP < 14.5mmHg and mean HbA1c of 8.1±1.1, while 72 subjects had an IOP ≥ 14.5mmHg and a mean HbA1c of 9.0±2.1. Although there was an overlap in the confidence intervals, a significant difference (P = 0.01) in the mean HbA1c level was observed in regression analysis between the two groups. Importantly, diabetic subjects with elevated HbA1c levels rarely (<1%) exhibited reduced IOP levels.

Conclusions

Diabetic subjects with elevated HbA1c levels exhibited significantly higher IOPs compared to those with lower HbA1c levels. Findings from this study indicate an association between hyperglycemia and elevated IOP and that poor glycemic control may contribute to increased IOP levels in long-term diabetic patients.

Assessment of Corneal Biomechanical Properties by CorVis ST in Patients with Dry Eye and in Healthy Subjects

Purpose. To investigate corneal biomechanical properties in patients with dry eye and in healthy subjects using Corneal Visualization Scheimpflug Technology (CorVis ST). Methods. Biomechanical parameters were measured using CorVis ST in 28 eyes of 28 patients with dry eye (dry eye group) and 26 normal subjects (control group). The Schirmer I test value, tear film break-up time (TBUT), and corneal staining score (CSS) were recorded for each eye. Biomechanical properties were compared between the two groups and bivariate correlation analysis was used to assess the relationship between biomechanical parameters and dry eye signs. Results. Only one of the ten biomechanical parameters was significantly different between the two groups. Patients in the dry eye group had significantly lower highest concavity time (HC-time) (P = 0.02) than the control group. Correlation analysis showed a significant negative correlation between HC-time and CSS with marginal P value (ρ = −0.39, P = 0.04) in the dry eye group. Conclusions. The corneal biomechanical parameter of HC-time is reduced in dry eyes compared to normal eyes. There was also a very weak but significant negative correlation between HC-time and CSS in the dry eye group, indicating that ocular surface damage can give rise to a more compliant cornea in dry eyes.