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Introduction: Corneal biomechanics is a relatively new discipline of research that focuses on the physical and biological interactions in the anterior part of the eye. Corneal biomechanics is influenced by a wide range of variables, including environmental influences, hydration, and hormone changes. Central Corneal Thickness (CCT), Intraocular Pressure (IOP), and age are other variables that might impact the corneas. The biomechanical properties of the cornea, at any level of cell to tissue to the sub-organ, might cause serious corneal diseases. Aim: To measure the corneal biomechanial properties in healthy Saudi females. Materials and Methods: This cross-sectional study was conducted in the Department of Optometry and Vision Science, College of Applied Medical Science, King Saud University, Riyadh, Saudi Arabia on 53 right eyes of Saudi female participants from April 2021 to April 2022. The IOP, CCT, and the corneal biomechanical properties at the first applanation (time- T1, velocity-V1, length-L1, deformation amplitude-DA1), second applanation (time-T2, velocity-V2, length-L2, deformation amplitude-DA2), highest concavity (Highest Concavity Time-HCT, Highest Concavity Radius-HCR, Highest Concavity Deformation Amplitude-HCDA), and Peak Distance (PD) were evaluated by using Corneal Visualisation Scheimpflug Technology (CST) whereas, Ocular Response Analyser (ORA) was used for the comparison of biomechanical properties. The statistical analysis of the data was done by applying statistical package IBM Statistical Package for the Social Sciences (SPSS) (version 24) and conducting Analysis of Variance (ANOVA) tests. Results: The mean age of the participants was 20.74±1.89 years, mean Spherical Equivalent (SE) refraction was -1.41±1.97 Diopters (D), the mean IOP was 16.82±1.96 mmHg, and the mean CCT was 569.43±27.22 µm for the right eyes. The results showed that the two most affecting factors in the biomechanical parameters were IOP and CCT. A potential association was found between first applanation time (T1) and corneal speed during the first applanation (V1) for both IOP and CCT (p<0.001) in the linear regression analysis, while a significant difference was observed in V1 (p=0.029) in SE. In the second applanation, a significant association was found in T2 with IOP (p<0.001) and CCT, cord length of the second applanation (L2) with CCT, and V2 with SE, IOP, and CCT was observed. A significant association between time and SE (p=0.034) was notice in the highest concavity parameter. However, deformation amplitude exhibited the significant association between SE and IOP, radius with IOP and CCT, and the PD with SE, IOP, and CCT (p<0.001). Conclusion: Most of the corneal biomechanical parameters were affected with CCT and IOP. Thus, the biomechanical characteristics of the cornea can be used to compare normal eyes with pathological eyes. [ABSTRACT FROM AUTHOR]

Abstract Corneal hysteresis (CH) is associated with glaucomatous structural changes. We retrospectively investigated the association between CH and the regional circumpapillary retinal nerve fibre layer thickness (cpRNFLT) in 419 eyes of 419 patients with normal-tension glaucoma (NTG) and primary open-angle glaucoma (POAG). CH was used as the explanatory variable, and cpRNFLT (total and quadrant) was used as the dependent variable. Standardized β coefficients were compared both overall and between the NTG and POAG groups. Multiple regression analysis with CH as the explanatory variable and cpRNFLT parameters as the dependent variables suggested that even after adjusting for age, sex, intraocular pressure (IOP), axial length, and central corneal thickness, all areas of the cpRNFLT were significantly associated with CH, except for the nasal quadrant. In the stratified analysis by glaucoma type, a positive relationship between CH and regional cpRNFLT tended to be maintained in the NTG group but not in the POAG group (P = 0.060 for interaction). Additionally, in the NTG group, the CH-inferior cpRNFLT relationship was particularly strong in the less-IOP fluctuation group. These results suggest that CH may be a potential predictor of anatomical vulnerability around the optic nerve, particularly enhancing the inferior regions of NTG.

Corneal hysteresis (CH) is associated with glaucomatous structural changes. We retrospectively investigated the association between CH and the regional circumpapillary retinal nerve fibre layer thickness (cpRNFLT) in 419 eyes of 419 patients with normal-tension glaucoma (NTG) and primary open-angle glaucoma (POAG). CH was used as the explanatory variable, and cpRNFLT (total and quadrant) was used as the dependent variable. Standardized β coefficients were compared both overall and between the NTG and POAG groups. Multiple regression analysis with CH as the explanatory variable and cpRNFLT parameters as the dependent variables suggested that even after adjusting for age, sex, intraocular pressure (IOP), axial length, and central corneal thickness, all areas of the cpRNFLT were significantly associated with CH, except for the nasal quadrant. In the stratified analysis by glaucoma type, a positive relationship between CH and regional cpRNFLT tended to be maintained in the NTG group but not in the POAG group (P = 0.060 for interaction). Additionally, in the NTG group, the CH-inferior cpRNFLT relationship was particularly strong in the less-IOP fluctuation group. These results suggest that CH may be a potential predictor of anatomical vulnerability around the optic nerve, particularly enhancing the inferior regions of NTG. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the changes in corneal biomechanical properties and tear film layer analysis after upper eyelid blepharoplasty surgery. Method: Sixty eyes of 30 patients were included in our prospective study. Corneal hysteresis (CH), corneal resistance factor (CRF), corneal compensated intraocular pressure (IOPcc) and Goldmann intraocular pressure (IOPg) measurements were taken with the Ocular Response Analyzer (ORA) device at the preoperative, postoperative 1st and 3rd months. The ocular surface was evaluated with tear breakup time (TBUT) and Ocular Surface Disease Index (OSDI) scores. Lid crease (LC), margin-to-reflex distance 1 (MRD1), and palpebral fissure height (PFH) were evaluated at each visit. Results: In the ORA analysis, in the 1st month CH value was found to be significantly lower than the preoperative value (preoperative 13.39 ± 6.08 mmHg; 1st month 10.74 ± 1.94 mmHg, p = 0.011). In addition, there was a statistically significant decrease in the 3rd month value compared to the preoperative values (10.46 ± 1.69 mmHg, p = 0.021). However CRF decreased postoperatively, no statistical difference was detected (preop 12.59 ± 3.84; 1st month 11.94 ± 3.04; 3rd month 9.78 ± 1.74; p = 0.149). While there was a decrease in IOPcc and IOPg in the postoperative period, no statistical difference was detected (respectively p = 0.96, p = 0.71). In the postoperative 1st month, TBUT increased significantly (p = 0.024). When those with a TBUT value below 10 were considered dry eye, significant decrease was observed in the percentage of dry eye in the first postoperative month (p = 0.027). Although the dry eye percentage decreased in the 3rd month compared to the preoperative percentage, no statistical difference was detected (p = 0.125). There was a significant decrease in the number of those with an OSDI score above 13 in the first month (p = 0.004). Conclusion: In our study, a decrease in ORA values was observed after blepharoplasty, with only CH being statistically significant. Reducing the load on the cornea after surgery may change the corneal biomechanics. These changes should be taken into consideration after eyelid surgery, especially in patients who may require glaucoma follow-ups. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Introduction: Research assuming linearity has concluded that corneal biomechanics are compromised in high myopia. We investigated whether this assumption was appropriate and re‐examined these associations across different levels of myopia. Methods: Myopic (spherical equivalent refraction, SER ≤ −0.50 D) eyes of 10,488 adults aged 40–69 years without any history of systemic and ocular conditions were identified in the UK Biobank. Ordinary least squares (OLS) regression was employed to test the linear association between corneal hysteresis (CH) or corneal resistance factor (CRF), separately, and SER while controlling for age, sex, corneal radius and intraocular pressure. Quantile regression (QR) was used to test the same set of associations across 49 equally spaced conditional quantiles of SER. Results: In OLS regression, each standard deviation (SD) decrease in CH and CRF was associated with 0.08 D (95% CI: 0.04–0.12; p < 0.001) and 0.10 D (95% CI: 0.04–0.15; p < 0.001) higher myopia, respectively. However, residual analysis indicated that the linearity assumption was violated. QR revealed no evidence of a significant association between CH/CRF and SER in low myopia, but a significant (p < 0.05) positive association became evident from −2.78 D (0.06 and 0.08 D higher myopia per SD decrease in CH and CRF). The magnitude of association increased exponentially with increasing myopia: in the −5.03 D quantile, every SD decrease in CH and CRF was associated with 0.17 D (95% CI: 0.08–0.25; p < 0.001) and 0.21 D (95% CI: 0.10–0.31; p < 0.001) higher myopia. In the −8.63 D quantile, this further increased to 0.54 D (95% CI: 0.33–0.76; p < 0.001) and 0.67 D (95% CI: 0.41–0.93; p < 0.001) higher myopia per SD decrease in CH and CRF. Conclusions: Corneal biomechanics appeared compromised from around −3.00 D. These changes were observed to be exponential with increasing myopia. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the impact of the cornea's biomechanical properties, corneal hysteresis (CH), and corneal resistance factor (CRF) on postoperative astigmatism after cataract surgery and determine the other factors that influence it. Forty eyes of 40 patients (13M/27F; the median age of 74) were included in this prospective study, underwent 2.75 mm incision cataract surgery, and were followed for 30 days. Visits were scheduled at baseline before surgery (V0), the 1st (V1), the 7th (V2), and the 30th (V3) postoperative days. The main parameters estimated and analyzed with Statistica® 14.0.1 were CH, CRF, astigmatism diopter, and axis. Following the cataract surgery, the CH did not significantly change during the study visits (p = 0.109). However, there was a significant change in the CRF from baseline during the study visits (per protocol set) (p = 0.002). After a slight but insignificant increase from V0 to V1, post hoc analysis found a significant decrease in the mean CRF from V1 to V2 (p = 0.049) with no substantial change from V2 to V3. According to the post hoc analysis, the median astigmatism diopter increased significantly only from V0 to V1 (p = 0.001) and slightly but not significantly decreased to the end of the study with the achievement of a near-baseline value. The main predictors for the final astigmatism diopter (R2 = 0.898) obtained by stepwise regression analysis were its values at V0, V1, and V2 (p < 0.001). The CRF at V1 was marginally significant, with a negative parameter estimate of −0.098303 (p = 0.0623). In conclusion, there was no correlation between preoperative CH and CRF and postoperative astigmatism using 2.75 mm incision cataract surgery. However, the final astigmatism diopter's main predictors were its baseline values before cataract surgery, the first, and the seventh postoperative days. [ABSTRACT FROM AUTHOR]

Abstract To analyze the changing trend of CH and CRF values under different influencing factors in T2DM patients. A total of 650 patients with T2DM were included. We discovered that the course of T2DM, smoking history, BMI, and FBG, DR, HbA1c, TC, TG, and LDL-C levels were common risk factors for T2DM, while HDL-C levels were a protective factor. Analyzing the CH and CRF values according to the course of diabetes, we discovered that as T2DM continued to persist, the values of CH and CRF gradually decreased. Moreover, with the increase in FBG levels and the accumulation of HbA1c, the values of CH and CRF gradually decreased. In addition, in patients with HbA1c (%) > 12, the values of CH and CRF decreased the most, falling by 1.85 ± 0.33 mmHg and 1.28 ± 0.69 mmHg, respectively. Compared with the non-DR group, the CH and CRF values gradually decreased in the mild-NPDR, moderate-NPDR, severe-NPDR and PDR groups, with the lowest CH and CRF values in the PDR group. In patients with T2DM, early measurement of corneal biomechanical properties to evaluate the change trend of CH and CRF values in different situations will help to identify and prevent diabetic keratopathy in a timely manner.

PrecisA lower baseline corneal hysteresis and a decrease in corneal resistance factor (CRF) over time are associated with higher risk of visual field progression in glaucomatous and glaucoma suspect eyes.PurposeThe aim was to investigate the longitudinal change in CRF and cornea hysteresis (CH) as risk factors for visual field progression.Materials and methodsIn this prospective observational cohort study, 72 eyes of 48 glaucoma or glaucoma suspect patients were followed for an average of 4.5 years. Baseline and follow-up CH and CRF measurements were performed with the Ocular Response Analyzer (Reichert Ophthalmic Instruments Inc., Depew, N.Y.). Evaluation of rates of visual field change during follow-up was performed using visual field mean deviation. Univariable and multivariable linear mixed models assessed the relationship of visual field progression with baseline CRF and CH as well as with changes in CRF and CH.ResultsThe mean baseline CH was 9.0 (95% confidence interval: 8.6-9.4)  mm Hg and the mean baseline CRF was 9.3 (95% confidence interval: 8.8-9.9) mm Hg. There was no statistically significant difference in average CH and CRF measurements over time. In multivariable modeling adjusting for age, race, and mean intraocular pressure during follow-up, each 1 mm Hg lower in baseline CH and 1 mm Hg decrease in CRF over time were associated with a 0.12 (P=0.042) and 0.14 dB/year (P=0.007) faster rate of visual field mean deviation loss, respectively. Similar findings were found in glaucoma eyes but not found in glaucoma suspect eyes.ConclusionVisual field progression was associated with a lower baseline CH and a decrease in CRF over time. Assessment of corneal resistance and elasticity at baseline and during follow-up examinations should be considered to identify those eyes at highest risk of visual field progression.

Over the last two decades, there has been growing interest in assessing corneal biomechanics in different diseases, such as keratoconus, glaucoma, and corneal disorders. Given the interaction and structural continuity between the cornea and sclera, evaluating corneal biomechanics may give us further insights into the pathogenesis, diagnosis, progression, and management of glaucoma. Therefore, some authorities have recommended baseline evaluations of corneal biomechanics in all glaucoma and glaucoma suspects patients. Currently, two devices (Ocular Response Analyzer and Corneal Visualization Schiempflug Technology) are commercially available for evaluating corneal biomechanics; however, each device reports different parameters, and there is a weak to moderate agreement between the reported parameters. Studies are further limited by the inclusion of glaucoma subjects taking topical prostaglandin analogues, which may alter corneal biomechanics and contribute to contradicting results, lack of proper stratification of patients, and misinterpretation of the results based on factors that are confounded by intraocular pressure changes. This review aims to summarize the recent evidence on corneal biomechanics in glaucoma patients and insights for future studies to address the current limitations of the literature studying corneal biomechanics. [ABSTRACT FROM AUTHOR]

Background and Objectives: Hyperopia is a refractive error which affects cognitive and social development if uncorrected and raises the risk of primary angle-closure glaucoma (PACG). Materials and Methods: The study included only the right eye—40 hyperopic eyes in the study group (spherical equivalent (SE) under pharmacological cycloplegia over 0.50 D), 34 emmetropic eyes in the control group (SE between −0.50 D and +0.50 D). A complete ophthalmological evaluation was performed, including autorefractometry to measure SE, and additionally we performed Ocular Response Analyser: Corneal Hysteresis (CH), Corneal Resistance Factor (CRF); specular microscopy: Endothelial cell density (CD), Cell variability (CV), Hexagonality (Hex), Aladdin biometry: Anterior Chamber Depth (ACD), Axial Length (AL), Central Corneal Thickness (CCT). IBM SPSS 26 was used for statistical analysis. Results: The mean age of the entire cohort was 22.93 years (SD ± 12.069), 66.22% being female and 33.78% male. The hyperopic eyes had significantly lower AL, ACD, higher SE, CH, CRF. In the hyperopia group, there are significant, negative correlations between CH and AL (r −0.335), CRF and AL (r −0.334), SE–AL (r −0.593), ACD and CV (r −0.528), CV and CRF (r −0.438), CH (r −0.379), and positive correlations between CCT and CH (r 0.393) or CRF (r 0.435), CD and ACD (r 0.509) or CH (0.384). Age is significantly, negatively correlated with ACD (r −0.447), CH (r −0.544), CRF (r −0.539), CD (r −0.546) and positively with CV (r 0.470). Conclusions: Our study suggests a particular biomechanical behavior of the cornea in hyperopia, in relation with morphological and endothelial parameters. Moreover, the negative correlation between age and ACD suggests a shallower anterior chamber as patients age, increasing the risk for PACG. [ABSTRACT FROM AUTHOR]

Purpose: Analysis of remote clinical functional results of high myopia correction in patients with thin cornea by method of intrastromal MyoRing implantation with Femtolaser assistance.Materials and methods. 22 eyes of 22 patients were included into investigation, the мean age of patients was 30.20 ± 5.37 (from 24 to 40) years. Mean spherical equivalent (SE) of refraction was –11.52 ± 1.96 D, cylindrical component of refraction was –2.04 ± 1.64 D. Minimal pachymetry index in center was 491.6 ± 20.0 mkm. Corneal hysteresis (CH) was 8.60 ± 1.19 mm Hg. The average pupil diameter in mesopic conditions was 5.60 ± 0.23 mm. All patients had a history of mild amblyopia. Period of control in average 2 years.Results. In 2 years after the surgery uncorrected visual acuity was 0.60 ± 1.22, corrected visual acuity 0.70 ± 0.20. Mean spherical equivalent (SE) of refraction was 0.61 ± 1.43 D, cylindrical component of refraction was –0.13 ± 0.50 D. Predictability of SE within ±0.5 D was 84 %, ±1.0 — 84 %. Index of safety was 1.16, index of efficacy — 1.0. CH was 9.50 ± 0.03 mm Hg. Mean pachymetry at center after the surgery did not change statistically significant in comparison with initial data (p = 1.00).Conclusion. MyoRing implantation is an effective and safe method, it provides: refraction spherical component correction, astigmatism correction and CH increase (p = 0.01).

Glaucoma is a leading cause of irreversible blindness in the world and its specific pathogenesis is not clear. More attention has been paid to intraocular pressure and aqueous outflow channel. In recent years, scholars began to attach more importance to the role of non-pressure dependent factors, such as corneal hysteresis(CH), in glaucoma. CH is a biomechanical parameter of cornea, which reflects the viscous resistance of cornea, i.e., the ability to absorb and disperse energy. CH can be easily acquired clinically and may serve as surrogate markers for biomechanical properties of tissues in the back of the eye, like the lamina cribrosa and peripapillary sclera, which may be related to the susceptibility of glaucomatous damage. Several studies have provided evidence of the associations between CH and clinically relevant outcomes in glaucoma. This article reviews the latest findings on CH and summarizes the measurement methods of CH, relations between CH and central corneal thickness, glaucomatous visual field progress, optic disc damage, retinal nerve fiber layer loss, etc.

This study investigated the influence of asymmetric corneal hysteresis (CH) on asymmetric visual field impairment between right and left eyes in patients with primary open-angle glaucoma (POAG) without a history of intraocular surgery. CH, corneal resistance factor (CRF), and corneal compensated intraocular pressure (IOPcc) were measured using the Ocular Response Analyzer. Differences between the eyes (right eye–left eye: DIFRL) and CH-based and in target parameters (higher CH eye–lower CH eye: DIFCH) were calculated in the same patient. In 242 phakic eyes of 121 patients, older age (p < 0.001), lower CH (p = 0.001), and lower CRF (p = 0.007) were significantly associated with worse standard automated perimetry (SAP) 24-2 mean deviation (MD). The DIFsRL in axial length (p = 0.003), IOPcc (p = 0.028), and CH (p = 0.001) were significantly associated with the DIFRL in SAP24-2 MD, but not in central corneal thickness (CCT), Goldmann applanation tonometry (GAT) measurement, and CRF. When dividing the patients into two groups based on the median of the CH DIFsCH (0.46), the DIFsCH in CRF (p < 0.001), IOPcc (p < 0.001), CCT (p = 0.004), SAP24-2 MD (p < 0.001), and SAP10-2 MD (p = 0.010) were significantly different between the groups. Large inter-eye asymmetry in CH is an important explanatory factor for disease worsening in patients with POAG. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the corneal biomechanical properties and central corneal thickness in patients with Graves' orbitopathy (GO). Method: A total of 132 eyes of 66 patients with GO and 108 eyes of 54 healthy subjects were enrolled. Eyes with GO were classified as high score clinical activity score (CAS, ≥ 3) (Group 1, n = 64) and low CAS score (< 3) (Group 2, n = 68). Corneal biomechanical parameters [corneal hysteresis (CH), corneal resistance factor (CRF)], Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated IOP (IOPcc) levels were measured with Ocular Response Analyzer (ORA, Reichert Ophthalmic Instruments, Buffalo, NY) and compared between the groups. Results: The mean CH values were found as 9.6 ± 1 mmHg in Group 1, 10.2 ± 0.9 mmHg in Group 2, and 11.4 ± 1.7 mmHg in the Control Group (p < 0.001). In post hoc analysis the mean CH was significantly lower in Group 1 than Group 2 and Control Group (Group 1-Group 2, p < 0.001; Group 1-Control Group, p < 0.001). The mean CRF was found as 10.5 ± 2.1 in Group 1, 10.4 ± 2.2 in Group 2, and 10.43 ± 2.0 in the Control group. There was no statistically significant difference between the groups in CRF measurements (p = 0.959). The mean IOPcc values were found as 17.1 ± 3.6 mmHg in Group 1, 15.8 ± 4.0 mmHg in Group 2 and 15.2 ± 4.1 mmHg in the Control Group. The IOPcc and IOPg measurements between all groups were statistically significant (p = 0.009, p = 0.027, respectively). Conclusions: Corneal biomechanical measurements were different in the GO patients with varying CAS scores compared to healthy individuals. [ABSTRACT FROM AUTHOR]

Purpose of reviewTo summarize the ocular and systemic associations of floppy eyelid syndrome (FES) as well as provide an up-to-date review on the pathogenesis and treatment strategies.Recent findingsVirtually all patients with FES have obstructive sleep apnea (OSA). However, a significantly lower proportion of patients with OSA have FES. Although some studies demonstrate no association between OSA and FES, almost all show at least an association with increased eyelid laxity, which may be a less severe form of FES. FES has also been associated with keratoconus (KCN) and glaucoma. Decreased corneal hysteresis has been found in FES, KCN, glaucoma, and OSA and may be related to matrix metalloproteinase (MMP) upregulation. Hypoxia-reperfusion injury, leptin resistance, and mechanical forces all may lead to increased MMP activity, contributing to elastin breakdown in the tarsus and other tissues throughout the body. Management of FES begins with investigation for OSA. Treating OSA with continuous positive airway pressure (CPAP) or surgical uvulopalatoplasty may improve FES. Surgical treatments for FES should reduce horizontal eyelid laxity while maximizing the stability of the tarsus. Collagen crosslinking may prove a helpful modality for stabilizing the tarsus in the future.SummaryFES is associated with OSA, glaucoma, and KCN. MMP upregulation and lower corneal hysteresis have been found in these conditions, pointing toward a potential common pathogenesis.

Purpose:To compare the intraocular pressure (IOP) measured with the Goldmann tonometer as the current standard of clinics with five different tonometers in healthy people, and to investigate the effect of corneal thickness and biomechanical properties on measurements.Methods:In this cross-sectional study, IOP was measured in 94 eyes of 94 healthy subjects with the Goldmann, manual applanation resonance, Icare, Topcon non-contact, Ocular Response Analyzer and Corvis’s tonometers. Comparison of the IOPs measured with different techniques was done using the repeated measures analysis of variance while the central corneal thickness as a covariate. The Bland-Altman plots and intraclass correlation coefficients were used to assess the agreement between the measurements. Limits of agreement were determined as the mean difference ±1.96 SD. Regression analysis was used to estimate the effect of central corneal thickness, corneal hysteresis, and corneal resistance factor on IOPs obtained using different tonometers.Results:The lowest mean IOP was obtained with the Goldmann tonometer (13.1 ± 2.6 mmHg) and the highest with the Topcon non-contact tonometer (17.3 ± 2.5 mm Hg). There was a statistically significant difference between the pressure measured by Goldmann's tonometer and other tonometers. The mean IOP measured using Icare (14.6 ± 3.4 mmHg) demonstrated the smallest mean difference and the highest agreement with the Goldmannn tonometer results. Central corneal thickness significantly affected all IOPs except the cornea-compensated IOP (IOPcc). The highest influence of IOP on the corneal resistance factor was related to Topcon non-contact tonometer and Goldmann correlated IOP (IOPg), while the lowest was seen with IOPcc and Goldmann.Conclusions:The Icare tonometer had the highest agreement among the different tonometers with the Goldmann tonometer. The central thickness of the cornea affects the results of all tonometers except IOPcc. Among the two evaluated corneal biomechanical parameters, the corneal resistance factor was the only biomechanical parameter effective on IOPs measured with all devices.

To review the current published literature on the utility of corneal hysteresis (CH) to assist the clinician in the diagnosis of glaucoma or in the assessment of risk for disease progression in existing glaucoma patients. Searches of the peer-reviewed literature in the PubMed database were performed through July 2022. The abstracts of 423 identified articles were examined to exclude reviews and non-English articles. After inclusion and exclusion criteria were applied, 19 articles were selected, and the panel methodologist rated them for level of evidence. Eight articles were rated level I, and 5 articles were rated level II. The 6 articles rated level III were excluded. Corneal hysteresis is lower in patients with primary open-angle glaucoma, primary angle-closure glaucoma, pseudoexfoliative glaucoma, and pseudoexfoliation syndrome compared with normal subjects. Interpretation of low CH in patients with high intraocular pressure (IOP) or on topical hypotensive medications is complicated by the influence of these parameters on CH measurements. However, CH is also lower in treatment-naïve, normal-tension glaucoma patients compared with normal subjects who have a similar IOP. In addition, lower CH is associated with an increased risk of progression of glaucoma based on visual fields or structural markers in open-angle glaucoma patients, including those with apparently well-controlled IOP. Corneal hysteresis is lower in glaucoma patients compared with normal subjects, and lower CH is associated with an increased risk of disease progression. However, a causal relationship remains to be demonstrated. Nevertheless, measurement of CH complements current structural and functional assessments in determining disease risk in glaucoma suspects and patients. Proprietary or commercial disclosure may be found after the references. [ABSTRACT FROM AUTHOR]

Introduction: Corneal biomechanical properties could affect intraocular pressure (IOP) measurement. The aim of this study was to evaluate the differences in corneal biomechanical properties of various types of glaucoma, assess their effect on IOP measurements. Methods: This is an observational clinical study of 486 subjects including 102 normal subjects, 104 ocular hypertension (OHT), 89 normal tension glaucoma (NTG), and 191 high tension glaucoma (HTG). Corneal biomechanical parameters were measured using an ocular response analyzer. The main parameters assessed were corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated pressure measurement (IOPg), and corneal-compensated intraocular pressure (IOPcc). Ultrasound pachymetry was used to measure central corneal thickness (CCT). IOP was measured by a Goldmann applanation tonometer (GAT) and a noncontact tonometer (NCT). Visual field (VF) and refractive status were also recorded. Results were analyzed by one-way analysis of variance, univariate and multivariate linear regression analyses, and Bland-Altman plots. Results: Multiple comparison by analysis of variance showed significantly lower CH and CRF in NTG compared to HTG, OHT, and normal subjects (CH: 0.011, 0.015, and 0.033; CRF: 0.001, <0.001, and 0.042, respectively). CRF and CH associated with IOP were measured using either GAT, NCT and IOPcc-GAT, IOPcc-NCT, yet CCT was not. GAT correlated strongly with IOPg (r = 0.79; p < 0.001) and IOPcc (r = 0.77; p < 0.001), but limits of agreement between the measurements were poor. CH and CRF were both negatively correlated with VF change (p < 0.01). Conclusion: CH and CRF affect the measurement of IOP and were related to types of glaucoma or severity of glaucoma. Pure CCT should not be used to correct IOP values or estimate the risk of disease. [ABSTRACT FROM AUTHOR]

The mechanism of action underlying prostaglandin analog (PGA) therapy involves changes in the expression of different metalloproteases to increase permeability of the sclera and allow increased aqueous humor outflow through this alternative drainage pathway. This alteration of structure impacts cornea/scleral biomechanics and may introduce artifact into the measurement of intraocular pressure (IOP) in the clinical setting. A literature search reviewing the impact of PGA therapy on corneal and scleral biomechanics was conducted including basic studies, clinical studies with treatment naïve patients, and a clinical study examining the cessation of PGA therapy. Additional literature including engineering texts was added for greater clarity of the concepts underlying ocular biomechanics. One study with an animal model reported significant corneal stiffening with PGA treatment. Most longitudinal clinical studies examining the effects of initiation of PGA therapy in PGA naïve subjects failed to report biomechanical parameters associated with stiffness using the Corvis ST and only included those parameters strongly influenced by IOP. One study reported a significant reduction in scleral stiffness with IOP as a co-variate, highlighting the need to account for the effects of IOP lowering when assessing clinical biomechanics. The report of cessation of PGA therapy on corneal biomechanics showed no change in corneal compensated IOP after 6 weeks, raising the question of reversibility of the PGA-induced structural alteration. Given that the findings in several clinical studies may merely reflect a reduction in IOP, further studies are warranted using Corvis ST parameters associated with corneal and scleral stiffness. The gold standard for IOP measurement in the clinical setting is Goldmann applanation tonometry, a technique previously shown to be affected by corneal stiffness. Since PGA therapy has been reported to alter not only scleral biomechanics, but also corneal biomechanics, it is essential to consider alternative tonometry technologies in the clinic. [ABSTRACT FROM AUTHOR]

The role of corneal biomechanics in laser vision correction (LVC) is currently being raised in the assessment of postoperative corneal ectasia risk. The aim of the paper was to evaluate the changes in corneal biomechanics after LVC procedures based on a systematic review of current studies. The results of a search of the literature in the PubMed, Science Direct, Google Scholar, and Web of Science databases were selected for final consideration according to the PRISMA 2020 flow diagram. Included in our review were 17 prospective clinical studies, with at least 6 months of follow-up time. Corneal biomechanical properties were assessed by Ocular Response Analyzer (ORA), or Corvis ST. The results of the study revealed the highest corneal biomechanics reduction after laser in situ keratomileusis (LASIK) followed by small incision lenticule extraction (SMILE) and surface procedures, such as photorefractive keratectomy (PRK) or laser-assisted sub-epithelial keratectomy (LASEK). In SMILE procedure treatment planning, the use of thicker caps preserves the corneal biomechanics. Similarly, reduction of flap thickness in LASIK surgery maintains the corneal biomechanical strength. Future prospective clinical trials with standardization of the study groups and surgical parameters are needed to confirm the results of the current review. [ABSTRACT FROM AUTHOR]

Introduction Ablation procedures used for vision correction such as photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) flap creation produce massive changes within the corneal structure and biomechanical properties. These changes are due to thinning of the central cornea and disruption of continuity of the collagen lamellae. Several approaches to assessment of the biomechanical properties have been proposed. Refractive photoablation procedures that decrease corneal hysteresis (CH) and corneal resistance factor (CRF) have been shown by several studies; therefore, here in our study we are going to discuss the effect of PRK versus LASIK on the corneal biomechanics and stability over time. Aim To compare the postoperative biomechanical properties of the cornea after PRK and after LASIK in eyes with moderate myopia. Patients and methods The study is 'prospective, controlled, and randomized.' In all, 40 eyes with moderate myopia (−2.0 to − 5.0 D) underwent refractive correction of myopia; 20 of them (group A) were enrolled for PRK while the other 20 of them (group B) were enrolled for LASIK surgery. CH and CRF were measured with an ocular response analyzer preoperatively and 1and 3 months postoperatively. All eyes were subjected to corneal topography preoperatively and 1 and 3 months postoperatively ocular response analyzer was used preoperatively and 1 and 3 months postoperatively. Results All patients were followed up postoperatively at 1 and 3 months. The CH and CRF were measured in both groups preoperatively and postoperatively. In group A, the mean preoperative CH was 10.7 ± 0.4 (range: 10–11.1) and CRF was 10.2 ± 0.11 (range: 10.1–10.5), whereas in group B it was 10.57 ± 0.38 (range: 10–11.2) and the CRF was 10.21 ± 0.1 (range: 10–10.5), respectively, with no significant difference (P = 0.43 and 0.25, respectively). After 1 month, CH and CRF were 8.4 ± 0.27 (range: 7.9–9.1) and 8.2 ± 0.23 (range: 7.8–8.6) in group A and 8.3 ± 0.25 (range: 8.0–9.0) and 8.17 ± 0.19 (range: 7.9–8.5) in group B, respectively, with no significant difference (P = 0.28 and 0.45, respectively). At 3 months, CH and CRF were 8.6 ± 0.28 (range: 8.1–9.2) and 8.3 ± 0.21 (range: 7.8–8.6) in group A and 8.55 ± 0.26 (range: 8.2–9.1) and 8.28 ± 0.18 (range: 7.9–8.6) in group B, respectively, with no significant difference (P = 0.56 and 0.32, respectively). The corneal biomechanical parameters decreased after both PRK and LASIK procedures. The corneal biomechanical parameters decreased after both PRK and LASIK procedures. The postoperative measurements of CH and CRF at 3 months were lower than the preoperative values in both groups with a significant amount (P < 0.001). Conclusion Both PRK and LASIK substantially weaken the biomechanical strength of the cornea, the greater the amount of myopic correction, the more the change in corneal biomechanics.

Background and Objectives: Hyperopia is a refractive error which affects cognitive and social development if uncorrected and raises the risk of primary angle-closure glaucoma (PACG). Materials and Methods: The study included only the right eye—40 hyperopic eyes in the study group (spherical equivalent (SE) under pharmacological cycloplegia over 0.50 D), 34 emmetropic eyes in the control group (SE between −0.50 D and +0.50 D). A complete ophthalmological evaluation was performed, including autorefractometry to measure SE, and additionally we performed Ocular Response Analyser: Corneal Hysteresis (CH), Corneal Resistance Factor (CRF); specular microscopy: Endothelial cell density (CD), Cell variability (CV), Hexagonality (Hex), Aladdin biometry: Anterior Chamber Depth (ACD), Axial Length (AL), Central Corneal Thickness (CCT). IBM SPSS 26 was used for statistical analysis. Results: The mean age of the entire cohort was 22.93 years (SD ± 12.069), 66.22% being female and 33.78% male. The hyperopic eyes had significantly lower AL, ACD, higher SE, CH, CRF. In the hyperopia group, there are significant, negative correlations between CH and AL (r −0.335), CRF and AL (r −0.334), SE–AL (r −0.593), ACD and CV (r −0.528), CV and CRF (r −0.438), CH (r −0.379), and positive correlations between CCT and CH (r 0.393) or CRF (r 0.435), CD and ACD (r 0.509) or CH (0.384). Age is significantly, negatively correlated with ACD (r −0.447), CH (r −0.544), CRF (r −0.539), CD (r −0.546) and positively with CV (r 0.470). Conclusions: Our study suggests a particular biomechanical behavior of the cornea in hyperopia, in relation with morphological and endothelial parameters. Moreover, the negative correlation between age and ACD suggests a shallower anterior chamber as patients age, increasing the risk for PACG.

Corneal biomechanical properties reflect the capacity of the cornea to respond to applied mechanical forces. They are an increasingly important domain in ocular pathology, correlated to the diagnosis and evolution of eye diseases such as refractive errors, glaucoma or corneal ectasias. Refractive errors constitute a significant etiology of decreased vision worldwide, with a particular impact in children. Myopic eyes significantly differ from emmetropic eyes in terms of morphology and biomechanics, with differences being reported in both adults and children. In the latter, corneal hysteresis (CH) and the corneal resistance factor (CRF) are significantly lower in myopic individuals, and both biomechanical parameters correlate with the central corneal thickness and axial length. Glaucoma is a progressive optic neuropathy that leads to thinning of the nerve fiber layer and specific visual field loss, in which intraocular pressure (IOP) is an important risk factor. There is an inverse correlation between IOP and CH - a low hysteresis is associated with a high IOP. Furthermore, CH is on average lower in primary open angle glaucoma (POAG) compared to ocular hypertension (OHT) for the same IOP. Significant correlations between CH and the thickness of the ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL), in both POAG and OHT, have been described. Keratoconus is the most frequent corneal ectasia, which leads to a progressive thinning and protruding of the cornea. Biomechanical parameters are severely affected in keratoconus - usually, both CH and CRF are lower compared to normal eyes. The biomechanical behavior of the cornea modulates the evolution of several ocular pathologies. As research is ongoing, more data will enable us to apply this knowledge in diagnosing disease more efficiently and targeting the right treatment for the right patient, including refractive surgery. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate corneal biomechanical changes after Descemet stripping automated endothelial keratoplasty (DSAEK), penetrating keratoplasty (PK), and phacoemulsification (PE). Methods: This prospective study included 138 eyes which underwent PK (26 eyes), DSAEK (26 eyes), PE (57 eyes), and 29 normal eyes. Intraocular pressure (IOP) was measured by Goldmann applanation tonometer (GAT), and central corneal thickness (CCT) and axial length by ultrasound. The ocular response analyzer was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-related IOP (IOPg), and cornea-compensated IOP (IOPcc) preoperatively and 1, 3, and 6 months postoperatively. Results: At baseline, PK group had the lowest CH and CRF. There was a significant increase in CH and CRF to normal values in PK (P = 0.015 and 0.006) and PE (P = 0.005 and 0.0001) groups over the study period. At 6 months, CH and CRF increased and reached normal values in the PK group; increased to a lower level than normal in the DSAEK group; and, after an initial reduction, increased to normal values in the PE group. At 6 months, DSAEK group had the lowest CH and CRF. There was a significant positive correlation between CRF and GAT (r = 0.281, P = 0.009), IOPg and GAT (r = 0.335, P = 0.001), and IOPcc and GAT (r = 0.282, P = 0.001). CH was negatively correlated with age (r = − 0.189, P = 0.04). Conclusion: Corneal biomechanical factors increase after DSAEK and PK. At post-operative month six, they reach normal values in PK group, but are lower than normal in DSAEK group. [ABSTRACT FROM AUTHOR]

Purpose: Corneal hysteresis (CH) and corneal resistance factor was found to be less for patient wearing toric contact lens as compared to soft spherical CH was calculated as the difference in air pressures between force-in applanation (P1) and force-out applanation (P2), or (P1–P2). Materials and Methods: This was the prospective study, 40 eyes of 22 patients with mean age of 22.09 ± 4.05 years. Eleven eyes were fitted with soft toric contact lens and 29 eyes were fitted with soft spherical contact lens. Dry eye, keratoconic or any systemic pathology were excluded. Soft toric and soft spherical contact lenses (Comfilcon A, Coopervision, and Southampton, UK) were fitted. The Ocular response Analyzer (Reichert Ophthalmic Instruments, Depew, New York, USA) was used to measure CH before and after 3 months using soft toric and soft spherical contact lenses. Descriptive statistics were used to analyze the demographic data. Paired t-test was employed for analyzing the difference between the base line value of CH with soft toric and soft spherical contact lens wearers after 3 months. Independent t-test was used to find the association between CH and gender. Results: CH was found to be lesser after 3 months of soft toric contact lens wear, as compared with soft spherical contact lenses. Mean increase of CH was found to range from 10.44 ± 0.96to 10.80 ± 0.96 mmHg (P = 0.000). Conclusion: In this study, there was a decrease in CH after using soft toric contact lenses and increase after using soft spherical contact lenses for 3 months. The increased CH with soft spherical contact lens was reversible in nature. However, CH may differ between lens type and modality of wear which can lead to long-term changes in the corneal biomechanical properties.

Purpose: To determine the distribution of corneal-compensated intraocular pressure (IOPcc), Goldmann-correlated intraocular pressure (IOPg) and their associated factors in a geriatric population. Methods: The present cross-sectional study was performed in individuals above 60 years of age in Tehran, the capital of Iran. The sampling was performed using multi-stage random cluster sampling method. All participants underwent preliminary ocular examinations, and then imaging by Pentacam HR and IOL master 500. Measurement of IOPg, IOPcc, and corneal biomechanical indices including corneal hysteresis (CH) and corneal resistant factor (CRF) was performed in a random sub-sample using ocular response analyzer (ORA). Results: The mean IOPg and IOPcc were 16.76 ± 4.71 mmHg and 19.05 ± 4.67 mmHg, respectively. There were no statistically significant differences in both IOPg (p = 0.891) and IOPcc (p = 0.248) between males and females. Based on the multiple linear regression models, both IOPg and IOPcc showed a statistically significant direct relationship with CRF (P < 0.001) and a significant inverse relationship with CH (P < 0.001 for IOPg and IOPcc), anterior chamber angle (ACA) (p = 0.006 for IOPg and p = 0.017 for IOPcc), and spherical equivalent refractive error (p = 0.032 for IOPg and p = 0.046 for IOPcc). Conclusion: Mean IOPg and IOPcc in the present study were higher compared to most previous studies. Corneal biomechanical indices including CH and CRF, refractive error and anterior chamber angle were independent associated factors of IOPg and IOPcc in the present study. There was no significant relationship between ORA-derived IOP values and CCT. [ABSTRACT FROM AUTHOR]

Biomechanics of the cornea have significant influences on the non-contact measurement of the intraocular pressure. The corneal behaviour during tonometry is a fundamental factor in estimating its value. The aim of the study was to analyse the behaviour of the cornea during tonometric measurement with the forced change in intraocular pressure during the water drinking test. Ocular Response Analyser (Reichert) was used to the measurement. Besides four basic parameters connected with intraocular pressure (IOPg, IOPcc) and biomechanics (corneal hysteresis CH and corneal resistance factor (CRF), other parameters representing the behaviour of the cornea during a puff of air were analysed. There were 47 eyes included in the study, including 27 eyes with a XEN GelStent implanted and 20 without it. The eyes of people with monocular implementation were the reference group. The values of analysed parameters were compared before and after 10, 25, 40, and 55 min after drinking the water. The intraocular pressure increased by 2.4 mmHg (p < 0.05) for eyes with a XEN stent and 2.2 mmHg for eyes without a stent (p < 0.05) in the tenth minute after drinking of water. This change caused a decreasing of corneal hysteresis (p < 0.05) without significant changes in the corneal resistance factor (p > 0.05). Corneal hysteresis changed similarly in the reference group and the group with a XEN GelStent. The analysis of additional parameters showed a difference in the behaviour of the cornea in eyes with a XEN GelStent in comparison to the corneas of eyes without a stent. This was particularly visible in the analysis of the cornea's behaviour during the second applanation, when the cornea returns to its baseline state after deformation caused by air puff tonometry. [ABSTRACT FROM AUTHOR]

PURPOSE: The purpose of the study was to evaluate the corneal biomechanical properties in patients post kidney transplant and to compare them with healthy age-matched control. MATERIALS AND METHODS: In this cross-sectional study, 68 patients with kidney transplant (study group) and 68 healthy individuals (control group) were analyzed with ocular response analyzer measurements. Only the right eye of each participant was assessed for corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc), and Goldmann-correlated intraocular pressure (IOPg). RESULTS: The mean CH in the study group was 9.70 ± 1.62 mmHg which was significantly lower than the control group with the mean CH of 10.60 ± 1.49 mmHg (P = 0.001). The mean IOPcc was 18.17 ± 4.00 mmHg and 16.00 ± 3.94 mmHg in the study and control groups, respectively (P = 0.002). CRF and IOPg were not significantly different between groups. CONCLUSION: CH and IOPcc are altered in kidney transplant patients.

It is known that as people age their tissues become less compliant and the ocular structures are no different. Corneal Hysteresis (CH) is a surrogate marker for ocular compliance. Low hysteresis values are associated with optic nerve damage and visual field loss, the structural and functional components of glaucomatous optic neuropathy. Presently, a range of parameters are measured to monitor and stratify glaucoma, including intraocular pressure (IOP), central corneal thickness (CCT), optical coherence tomography (OCT) scans of the retinal nerve fibre layer (RNFL) and the ganglion cell layer (GCL), and subjective measurement such as visual fields. The purpose of this review is to summarise the current evidence that CH values area risk factor for the development of glaucoma and are a marker for its progression. The authors will explain what precisely CH is, how it can be measured, and the influence that medication and surgery can have on its value. CH is likely to play an integral role in glaucoma care and could potentially be incorporated synergistically with IOP, CCT, and visual field testing to establish risk stratification modelling and progression algorithms in glaucoma management in the future. [ABSTRACT FROM AUTHOR]

Introduction: Ablation procedures used for vision correction such as photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) flap creation produce massive changes within the corneal structure and biomechanical properties. These changes are due to thinning of the central cornea and disruption of continuity of the collagen lamellae. Several approaches to assessment of the biomechanical properties have been proposed. Refractive photoablation procedures that decrease corneal hysteresis (CH) and corneal resistance factor (CRF) have been shown by several studies; therefore, here in our study we are going to discuss the effect of PRK versus LASIK on the corneal biomechanics and stability over time. Aim: To compare the postoperative biomechanical properties of the cornea after PRK and after LASIK in eyes with moderate myopia. Patients and methods: The study is 'prospective, controlled, and randomized.' In all, 40 eyes with moderate myopia (-2.0 to - 5.0 D) underwent refractive correction of myopia; 20 of them (group A) were enrolled for PRK while the other 20 of them (group B) were enrolled for LASIK surgery. CH and CRF were measured with an ocular response analyzer preoperatively and 1and 3 months postoperatively. All eyes were subjected to corneal topography preoperatively and 1 and 3 months postoperatively ocular response analyzer was used preoperatively and 1 and 3 months postoperatively. Results: All patients were followed up postoperatively at 1 and 3 months. The CH and CRF were measured in both groups preoperatively and postoperatively. In group A, the mean preoperative CH was 10.7 ± 0.4 (range: 10-11.1) and CRF was 10.2 ± 0.11 (range: 10.1-10.5), whereas in group B it was 10.57 ± 0.38 (range: 10-11.2) and the CRF was 10.21 ± 0.1 (range: 10-10.5), respectively, with no significant difference (P = 0.43 and 0.25, respectively). After 1 month, CH and CRF were 8.4 ± 0.27 (range: 7.9-9.1) and 8.2 ± 0.23 (range: 7.8-8.6) in group A and 8.3 ± 0.25 (range: 8.0-9.0) and 8.17 ± 0.19 (range: 7.9-8.5) in group B, respectively, with no significant difference (P = 0.28 and 0.45, respectively). At 3 months, CH and CRF were 8.6 ± 0.28 (range: 8.1-9.2) and 8.3 ± 0.21 (range: 7.8-8.6) in group A and 8.55 ± 0.26 (range: 8.2-9.1) and 8.28 ± 0.18 (range: 7.9-8.6) in group B, respectively, with no significant difference (P = 0.56 and 0.32, respectively). The corneal biomechanical parameters decreased after both PRK and LASIK procedures. The corneal biomechanical parameters decreased after both PRK and LASIK procedures. The postoperative measurements of CH and CRF at 3 months were lower than the preoperative values in both groups with a significant amount (P < 0.001). Conclusion: Both PRK and LASIK substantially weaken the biomechanical strength of the cornea, the greater the amount of myopic correction, the more the change in corneal biomechanics. [ABSTRACT FROM AUTHOR]

Larae Zimprich,1 Jacob Diedrich,2 Adam Bleeker,3 Justin A Schweitzer1 1Vance Thompson Vision, Sioux Falls, SD 57108, USA; 2Mijangos Optometry, Sioux City, IA 51106, USA; 3University of South Dakota Sanford School of Medicine, Vermillion, SD 57069, USACorrespondence: Justin A SchweitzerVance Thompson Vision, 3101 W 57th Street, Sioux Falls, SD 57108, USATel +1605-361-3937Fax +1605-371-7035Email justin.schweitzer@vancethompsonvision.comAbstract: The diagnosis and management of glaucoma has long been dependent on making decisions based on family history, optic nerve head evaluation, intraocular pressure, visual field testing, and optical coherence testing. Other pieces to aid in understanding glaucoma have presented throughout the years, including the role of corneal thickness. The discussion and debate on the mechanism of glaucoma have been attributed to resistance at the level of the conventional outflow pathway, perfusion pressure to the optic nerve head, cerebral spinal fluid pressure, and many more. Another piece that has emerged is corneal hysteresis, an assessment of the cornea’s ability to absorb and dissipate energy. There is abundant published literature supporting corneal hysteresis being associated with the presence and severity of glaucoma, the structural and functional progression of glaucoma, and the conversion to glaucoma. The supported data in these studies add another piece, corneal hysteresis, to consider in the diagnosis and management of glaucoma.Keywords: glaucoma, corneal hysteresis, corneal biomechanics

Purpose: To investigate the effect of "skin-only" upper eyelid blepharoplasty on corneal biomechanics and central as well as peripheral topographic/tomographic parameters before and 4 weeks after surgery. Methods: In a prospective study, the corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated before and after blepharoplasty. Corneal topographic (maximum simulated keratometry value, inferior-superior value, index of surface variance, index of vertical asymmetry, index of height asymmetry, index of height decentration) and tomographic parameters (corneal thickness, corneal astigmatism and mean 5-mm- and 7-mm-zone keratometry value) were measured by the Pentacam HR. Statistical analysis was performed using a linear mixed model considering correlated data of both eyes. Results: This study included 42 eyes of 35 patients (mean age: 64.5 years, range 52–82 years). Four weeks after surgery CH and CRF increased (9.4 ± 2.3 to 10.2 ± 2.2 mmHg and 9.7 ± 2.1 to 10.5 ± 2.2 mmHg) but did not reach statistical significance (P = 0.100 and P = 0.072). A significant increase in central maximum simulated keratometry value (Kmax) from 45.0 ± 2.3 to 45.4 ± 2.2 diopters (D) was observed (P = 0.004). Inferior-superior value (I-S) and index of surface variance (ISV) showed significant changes from 0.32 ± 0.98 to 0.10 ± 0.98 D (P = 0.02) and from 19.98 ± 9.84 to 22.93 ± 11.23 (P = 0.009), respectively. These alterations did not affect the subjective spherical equivalent (-0.09 ± 4.71 to -0.04 ± 4.51 D; P = 0.437) and the best-corrected distance visual acuity of patients (0.11 ± 0.14 to 0.15 ± 0.15 logMAR; P = 0.142). Age, gender and corneal thickness were not correlated with pre and postoperative differences of CH, CRF, corneal compensated IOP, Kmax, corneal astigmatism or I-S. Conclusion: The trend of increasing CH and CRF values might indicate a rise of corneal damping capacity. Despite statistically significant differences of Kmax, I-S and ISV, all other tomographical and topographical parameters did not change 4 weeks after surgery. The corneal steepening with a mean change of 0.4 diopters and the decrease of I-S with a mean of 0.22 diopters do not seem to have a clinically relevant effect for blepharoplasty patients in daily practice. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to determine the corneal biomechanical properties in patients with connective tissue disorders (CTDs) and compare them with age-matched healthy control. Materials and Methods: In this cross-sectional study, 62 patients (study group) with CTDs and 44 healthy patients (control) were analyzed by Ocular Response Analyzer (Reichert Inc., Depew, N. Y., USA) and Corneal Pachymetry (SP-2000, Tomey, Nagoya, Japan). The right eye of all patients was assessed for corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPc), and Goldmann-correlated intraocular pressure (IOPg), and central corneal thickness (CCT). Results: Mean CH (9.54 ± 1.66 mm Hg [study group] and 10.62 ± 1.21 mm Hg [control]; P = 0.013) and mean CRF (9.95 ± 1.47 mm Hg [study group] and 10.76 ± 1.25 mm Hg [control]; P = 0.040) were significantly different between groups. Mean IOPc, IOPg, and CCT were not significantly different between groups. In the subgroup analysis of study cases (oral steroid versus nonsteroid therapy) of CTDs, CRF which was significantly lower in steroid (9.25 mm Hg) compared nonsteroid therapy (10.20 mm Hg) (P = 0.045), whereas, other parameters such as CCT, CH, IOPc, and IOPg were comparable between the two groups (P ≥ 0.05). Conclusion: CH is altered in CTDs which may be an independent risk factor for glaucoma and might underestimate intraocular pressure so CH is an important consideration in patients with CTDs.s

Purpose: Evaluate potential corneal biomechanical changes following corneal crosslinking (CXL) by paired differential tonometry intraocular pressure (IOP) measurements with a Goldmann tonometer (GAT) prism and corneal compensating, correcting applanation tonometry surface (CATS) prism. Methods: IOP was measured prospectively on 23 unique eyes undergoing CXL for keratoconus with a GAT using a standard flat GAT prism and a curved corneal error correcting CATS prism before treatment and at 2 weeks, 2 months and 6 months after treatment. Concurrent measurements of central corneal thickness (CCT) and corneal hysteresis (CH) were completed. Results: Paired IOP measurements with standard GAT and corneal correcting CATS prisms indicated a significant sustained relative increase in the differential IOP between the two prisms after CXL (p =.002,0.051,0.062). CH initially decreased at two weeks post-CXL then returned to sustained pre-op levels (p =.033,0.20,0.20). CCT progressively decreased following CXL (p =.005). Discussion: Differential tonometry between standard GAT and corneal biomechanical compensating CATS prisms indicates findings consistent with increased corneal rigidity following CXL and may demonstrate a simple and sensitive method for measurement of relative corneal biomechanical changes due to pharmacologic agents and procedures. [ABSTRACT FROM AUTHOR]

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Purpose: To evaluate corneal hysteresis (CH), acquired with ocular response analyzer (ORA), as a risk factor for glaucoma progression in early-stage primary open-angle glaucoma (POAG). Methods: In a historical cohort study, patients diagnosed in 2011 with early-stage POAG according to the Hodapp, Parrish and Anderson classification modified for Octopus perimetry and followed up until glaucomatous progression development; otherwise, observations were censored in October 2018. Cox regression was used to obtain hazard ratios (HR) to evaluate baseline variables (CH, central corneal thickness, gender, age IOP and glaucoma family history) as risk factors for perimetric glaucoma progression. A likelihood ratio test for interaction was performed in order to assess the effect of the combination of CH and CCT on the risk of progression. Results: Of the cohort of 1573 patients, 11.38% developed early-stage POAG progression during the follow-up. The mean follow-up time was 3.28 ± 1.92 years. Patients without progression had a higher CH (11.35 ± 1.43 vs 9.07 ± 1.69 mmHg; p < 0.001) and CCT (570.75 ± 17.71 vs 554.51 ± 23.20; p < 0.001). In the multivariate analysis, each 1 mmHg of lower CH was associated with an increase of 2.13 times in the HR of progression (95% CI: 1.92–2.32; p < 0.001). CH hazard ratio was modified by CCT, with higher values of CCT and CH resulting in a higher HR of early glaucoma progression (p < 0.001). Conclusions: CH can be considered as a risk factor of progression in early-stage POAG. The risk associated with CH changed depending on CCT values, acting synergistically slowing the risk of glaucoma progression with higher values. [ABSTRACT FROM AUTHOR]

Abstract Background To evaluate corneal biomechanical properties by the Ocular Response Analyzer (ORA) in non keratoconic patients underwent penetrating keratoplasty (PK). Methods Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann- correlated intraocular pressure (IOPg), cornea-compensated IOP (IOPcc) using the ORA, and central graft thickness (CGT) were measured in 30 eyes at least two years after penetrating keratoplasty for non keratoconic indications. IOP using the Goldmann applanation tonometer (GAT) was also obtained after compensation for graft thickness and astigmatism. Results The mean age of patients was 33.1 ± 10.13 years; indications for PK were herpetic corneal scar (53.3%), corneal stromal dystrophy (23.3%), traumatic corneal opacity (10%), chemical corneal opacity (6.7%), and Fuchs endothelial dystrophy (6.7%). Mean CH and CRF were 8.52 ± 1.81 mmHg, and 8.56 ± 1.59 mmHg, respectively. Mean CGT was 532.43 ± 30 μm. Mean IOP GAT, IOPg, and IOPcc were 11.88 ± 3.66, 14.64 ± 4.08, and 17.27 ± 4.60 mmHg, respectively (P

INTRODUCTION[|]To determine the biomechanical and topographic alterations within the first year after accelerated crosslinking (CXL) treatment in patients with keratoconus.[¤]METHODS[|]In this prospective study, 52 eyes of 52 patients with progressive keratoconus underwent accelerated CXL were included. All patients had a detailed preoperative ophthalmologic examination, including slit-lamp evaluation, Goldmann tonometry, fundoscopy, topography by Scheimpflug imaging (Sirius), and corneal biomechanical evaluation with a biomechanical waveform analysis device (ORA). Alterations in visual acuity and topographic findings were evaluated before the treatment and at 12 months follow-up. Corneal biomechanical features were obtained before the treatment, and at 1st, 3rd, 6th and 12th months.[¤]RESULTS[|]Uncorrected-visual acuity and best-corrected visual acuity both statistically significantly improved at 12th month (p=0.001). There were no statistically significant differences in keratometry values, whereas maximum K (AKfront) and symmetry index front (SIfront) decreased significantly (p=0.015 and p=0.009, respectively). Corneal thinnest point and volume also decreased significantly at 12th month (p=0.001 for both). Goldmann-correlated intraocular pressure (IOPg) and corneal compensated IOP (IOPcc) values transiently increased in the first three months, while corneal hysteresis (CH) and the corneal resistance factor (CRF) transiently decreased, with the difference not statistically significant (p>0.05). However, central corneal thickness significantly decreased at the end of the 12th month (p=0.001).[¤]DISCUSSION AND CONCLUSION[|]Accelerated CXL seems to be effective in stopping the progression of keratoconus. Our findings showed transient alterations in biomechanical features, which will end with the preoperative values at the end of the 12th month. Further studies are needed to demonstrate the changes in corneal biomechanics in vivo.[¤]

The purpose is to assess the structural state of the cornea and pre-corneal lacrimal film in patients with myopia before refractive surgery, to identify the relationship with changes in cytokine concentration in the tear. Material and methods. 62 patients (124 eyes) with myopia were examined. The first group included 26 patients, only glasses were used for the correction of myopia, and in the 2nd group, 36 patients who used soft contact lenses during 5 to 15 years. Methods of examination: determination of the thickness of the corneal epithelium, height and width of the lacrimal meniscus, assessment of the biomechanical properties of the cornea, the Norn and Schirmer tests. Content of cytokines in the tear – interleukin 10 and tumor necrosis factor α – was measured using the test set «BEST» by enzyme immunoassay. Results. The decrease in the thickness of the epithelium of the cornea, the height and width of the lacrimal meniscus, the stability of the tear film, and the ratio of interleukin-10 to the tumor-α necrosis factor in patients who use contact lenses for a long time are revealed. The conclusion. Prolonged wearing of contact lenses for correction of myopia is accompanied by signs of symptomatic dry eye syndrome against a background of moderate oppression of the anti-inflammatory activity of tears.

AIM: To define the corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) prior to and following coaxial micro-incision phacoemulsification in patients with corneal astigmatism. METHODS: Of 97 patients with cataracts were enrolled in the study. Group 1 included patients with corneal astigmatism (K1-K2) values of K1-K2

Purpose: to investigate the average speed and risk factors for the glaucomatous optic neuropathy (GON) progression during longterm observation. Patients and methods. The 10-year data of 750 patients were analyzed. The average GON progression rate was calculated on the basis of perimetry and optical coherent tomography data. Further, according to inclusion and exclusion criteria 128 patients were included into the group of retrospective analysis. Resultes. The following risk factors were established: initial cornealcompensated IOP (IOPcc) > 23.6 mm Hg (AUC 0.7), IOPcc after 5 years > 19.8 mm Hg (AUC 0.83), age > 69.5 years (AUC 0.6), corneal hysteresis < 9.9 mm Hg (AUC 0.6) and retinal nerve fiber layer < 92 μm (AUC 0.6). Patients with pseudoexfoliation syndrome, and patients taking systemic calcium channel blockers (p = 0.01) also had the higher risk of GON progression. Its rate was lower in patients with arterial hypertension (p = 0.015), and in patients who received prostaglandin analogues (risk was 5 times reduced, p = 0.04) and fixed combinations (risk was 2 times reduced, p = 0.018). IOPcc of higher than 17.6 mm Hg in the long-term period is the most pronounced risk factor for the progression of GON. It was determined that the average ROP of glaucoma progression among the patients was 0.6 dB/year for ROP1, 0.62 ± 1.09 μm/year for ROP2 and 0.95 ± 3.28 μm/year for ROP3, also each 1 dB/year decrease in photosensitivity (in group with glaucoma progression) was associated with further loss of RNFL (3.9 µm/year). Conclusion. The use of prostaglandin analogues and fixed combinations reduces this risk.

Background and Objective: Keratoconus is a disorder in cornea characterized by constant thinning and prominence that can result in vision defect. Due to ultrasonic changes in the corneal structure caused by keratoconus disease, its rigidity and biomechanical properties are subject to some changes. In this regard, the present study was conducted to determine the correlation of biomechanical features of keratoconus patients with the severity of the disease. Materials and Methods: The case group was selected from the patients with keratoconus who referred to the Corneal Clinic of Nikookari Hospital in Tabriz and the controls had no eye diseases. Corneal biomechanics, corneal hysteresis, and corneal resistance factor were evaluated in all the samples using an ocular response analyzer device. Results: The present study was carried out on 213 keratoconus eyes and 179 normal eyes. The mean scores of corneal hysteresis were obtained at 13.49±1.34 and 7.67±1.01 mmHg for normal and keratoconus eyes, respectively, which were significantly different between the two groups. The differences between the corneal hysteresis of mild (8.86 mm Hg), moderate (8.30 mm Hg), and severe (7.10 mm Hg) keratoconus eyes were also significant. The mean scores of the corneal resistance factor were reported as 12.68±1.15 and 7.36±1.07 mmHg for normal and keratoconus eyes, respectively, which were significantly different between the two groups. The differences between the corneal resistance factor of mild (8.55 mm Hg), moderate (8.05 mm Hg), and severe (6.76 mm Hg) keratoconus eyes were also significant. Conclusion: The obtained results of the present study showed that corneal hysteresis and corneal resistance factor were lower in keratoconus eyes, compared to those in normal eyes and decreased with the severity of the disease.

PURPOSE: To evaluate biomechanical properties, corneal thickness, and intraocular pressure (IOP) in patients with rheumatoid arthritis (RA) and correlate them with rheumatoid activity. PATIENTS AND METHODS: Forty RA eyes were enrolled in a cross-sectional study. Clinical Disease Activity Index (CDAI) was used to assess the rheumatoid activity by a rheumatologist. Corneal hysteresis (CH), corneal resistance factor (CRF), and IOP corneal compensated, IOP Goldmann corrected were assessed using ocular response analyzer (ORA), Corneal thickness was measured using optical coherence tomography, and IOP using Goldman applanation tonometer (IOP GAT). RESULTS: There was a positive correlation between CH and CRF (P < 0.001 and r = 0.818) and (P < 0.001 and r = 0.714) in the active and inactive groups respectively, also between CRF and central corneal thickness (CCT) (P value 0.05 and r = 0.0435) in Inactive Group only. No correlation was found between CDAI score and ORA parameters. There was a negative correlation between CDAI and CCT in Active Group only (P < 0.001 and r = −0.823). CONCLUSION: Corneal biomechanical properties could be affected in rheumatoid patients in both active and remission phases, which may indicate that any corneal changes may be irreversible. These changes are of important significance regarding IOP measurement in rheumatoid patients. CCT may be a new parameter in the follow up of disease activity. [ABSTRACT FROM AUTHOR]

Purpose: The study evaluates the corneal biomechanical properties on Ocular Response Analyzer (ORA) and aims to establish their correlation with the clinical profile of patients with TAO. Methods: A tertiary care centre-based cross-sectional observational study was conducted. Eighty patients with stage I and II TAO (EUGOGO classification), categorized as group A, were age and sex matched with 85 controls constituting group B. The disease activity was assessed using clinical activity score (CAS). The thyroid hormonal profile of within one-week duration was recorded for each patient of group A. Mean IOP-GAT (IOP using Goldmann applanation tonometer), IOPg (Goldmann-correlated IOP value), IOPcc (cornea-compensated IOP value), CRF (corneal resistance factor), and mean corneal hysteresis (CH) of group A and B were compared. The variation of CH with disease severity, activity, and thyroid status in group A was evaluated. Results: Mean GAT, IOPg, and IOPcc of group A were significantly higher than that of group B (p <.001). Mean CH of group A i.e the visco-elastic dampening ability of cornea was significantly lower than that of group B (p <.001). In group A, mean CH of patients with stage 1 disease severity and CAS<3 was significantly higher than that of patients with stage 2 severity and CAS≥3 (p <.001). CH of hyperthyroid patients was significantly lower than CH of hypothyroid patients (p <.01). Conclusion: TAO affects the biomechanical properties of the globe as reflected by the corneal biomechanics on ORA. The disease severity, activity, and hyperthyroid status are negatively correlated with the CH. [ABSTRACT FROM AUTHOR]