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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., (© 2024. The Author(s).)

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., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

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.

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., (© 2024 The Authors. Ophthalmic and Physiological Optics published by John Wiley & Sons Ltd on behalf of College of Optometrists.)

Purpose: To investigate and compare the association of corneal hysteresis (CH) in patients with secondary glaucoma to control patients and patients with primary open-angle glaucoma (POAG). Additionally, to determine the consistency of CH measurements in patients with secondary glaucoma., Methods: A total of 84 patients (121 eyes) were prospectively included in this study. Twenty-three patients (46 eyes) were healthy controls, 24 patients (40 eyes) were diagnosed with POAG, and 27 patients (35 eyes) were diagnosed with a form of secondary glaucoma. CH and intraocular pressure (IOP) were measured using the Ocular Response Analyzer. Three measurements per eye were performed and used for the analysis and to determine fluctuations in CH data. One-way ANOVA with post-hoc Bonferroni analysis and Chi-Squared testing was done to determine differences between groups., Results: All patients were matched for age. Patients in both POAG and secondary glaucoma groups were matched for age and IOP. All groups had similar sex and racial compositions as well as similar proportions of diabetes, hypertension, and hyperlipidemia. CH was lower ( p  < .05) in patients with POAG (9.32 ± 1.64) and secondary glaucoma (7.89 ± 3.18) when compared to healthy controls (11.16 ± 1.60). Fluctuations in CH measurements were minimal in all groups. Further analysis of the secondary glaucoma group revealed no differences in CH between different types of secondary glaucoma ( p  > .05)., Conclusion: Patients with secondary glaucoma have lower CH when compared to POAG or control groups. The ORA exhibits precision of CH measurements for control, POAG, and secondary glaucoma groups, making it a reliable tool in management of secondary forms of glaucoma.

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., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

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.

Purpose: To compare corneal biomechanical properties measured with ocular response analyzer (ORA) and intraocular pressure (IOP) measurements in patients with vitamin D deficiency and in healthy cases., Methods: One hundred and twenty eyes of 120 subjects (between the ages of 19 and 78) who applied to university's outpatient clinic were evaluated: 41 lacks of vitamin D (Group 1), 39 insufficient vitamin D (Group 2) and 40 controls (Group 3). Corneal hysteresis, corneal resistance factor, Goldmann-correlated IOP and corneal compensated IOP of patients were measured by ORA., Results: The mean ages were 48.9 ± 12.1, 52.8 ± 13.6 and 52.1 ± 13.9 in groups 1, 2 and 3, respectively (p = 0.370). Mean IOPcc values were 16.5 ± 3.6 (8.1-27.3), 16.7 ± 2.7 (12.0-22.7) and 16.3 ± 3.3 (10.8-27.4) mmHg (p = 0.889); mean IOPg values were 16.8 ± 5.0 (6.5-39.5), 16.3 ± 2.9 (10.3-23.0) and 15.9 ± 3.2 (10.0-26.0) mmHg (p = 0.539); mean CH values were 10.8 ± 1.9 (8.3-19.0), 11.4 ± 1.6 (6.9-14.0) and 11.2 ± 1.5 (7.5-13.2) (p = 0.257); mean CRF values were 10.5 ± 2.7 (7.4-25.0), 11.1 ± 1.5 (6.8-13.5) and 10.5 ± 1.2 (7.7-12.8) (p = 0.282) in groups 1, 2 and 3, respectively. There was no statistical difference between the groups in terms of IOPcc, IOPg CH and CRF. However, mean CH values were found less in the lack of vitamin D group., Conclusion: The CH values were lower, and the IOPg values were higher in cases of vitamin D deficiency. Corneal biomechanical differences in patients with lack of vitamin D were not statistically significant.

Purpose: Clinically evaluate intraocular pressure (IOP) measurements taken with a Goldmann applanation tonometer (GAT) prism and a modified surface Goldmann prism examining measurement differences correlated to central corneal thickness (CCT) and corneal hysteresis (CH) values., Design: Prospective, open-label, randomised, controlled, multicentre reference device accuracy analysis., Methods: A GAT and a modified surface GAT prism measured IOP on 243 unique eyes. The study design and methodology complied with International Standard Organization (ISO) tonometer evaluation guidelines, except the inclusion of thin (<500 µm) and thick (>600 µm) corneas. All eyes were randomised to IOP measurement by one of five standard Goldmann prisms and five modified prisms. Pressures were measured by six investigators, two times with each prism for a total of 1936 IOP measurements. Analysis included a multiple linear regression including CCT and CH correlation., Results: The difference in IOP measurements of the standard and modified Goldmann prisms correlated well to CCT particularly in thin (<500 µm) and thick (>600 µm) corneas (R 2 =0.404, p=0.007). Corneal hysteresis (CH) also significantly correlated to the difference in prism measurements (R 2 =0.125, p=0.039). There was no significant overall mean IOP bias between the two prisms (+0.43 mm Hg in modified, p=0.19)., Discussion: The paired IOP measurement difference between GAT and a modified surface Goldmann replacement prism indicated a statistically significant correlation to CCT and CH. A simple modified replacement prism for any Goldmann-type tonometer may significantly improve IOP measurement accuracy by minimising corneal biomechanical errors associated with CCT and CH., Trial Registration Number: NCT02990169 and NCT02989909., Competing Interests: Competing interests: The submitted manuscript was completed by referencing studies funded by an NIH/NEI SBIR grant, 1R43 EY026821-01. Requirements of this grant are commercialisation of potentially beneficial ophthalmic/optometric medical devices/products. The commercialisation necessitates intellectual property and a company to produce the product. Commonly in new technology start-up companies, the corresponding author is also part owner in the intellectual property and the associated company (Intuor Technologies) producing the medical device. This is a conflict of interest. However, the authors attest to the stringent efforts made to provide unbiased information provided in this manuscript. We believe, as does the NIH and ASCRS, that the tonometer device has a potential to bring considerable value to the ophthalmic medical community and their patients., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

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 < 0.001). No significant association was found between CGT and IOP readings obtained using either the ORA or GAT. There were significant negative association between CH with both IOP GAT and IOPcc, while CRF had significant positive association with IOPg., Conclusion: After penetrating keratoplasty for non keratoconic patients, graft biomechanics does not return to average values even 2 years after the operation; moreover, intraocular pressure measurement with ORA gives higher values than thickness compensated GAT.

Purpose: To review and summarize the characteristics of corneal hysteresis (CH) and its relationship with glaucoma., Methods: A PubMed search was carried out using the terms "corneal hysteresis", "glaucoma", and "biomechanics". Up to March 2018, all studies published in English are included in this review., Results: The value of CH reflects the ability of corneal tissue to absorb and release energy during bidirectional flattening. It is an important biomechanical parameter of the cornea. The CH value of healthy adults is about 11 mmHg. The measurement of CH is reproducible and different. People have different CH values, which are determined by the shape of the individual's cornea. The study found that all types of glaucoma, including primary open angle glaucoma, angle-closure glaucoma, normal tension glaucoma, congenital glaucoma, binocular asymmetrical glaucoma, CH values are lower than normal people, therefore, CH is therefore a good indicator of glaucoma diagnosis and screening. Lower CH values are associated with thinner retinal nerve fiber layer (RNFL), larger linear cup/disk ratio (LCDR) and degree of optic disc defect. A lower CH value can also result in a lower visual field index. CH and the basic intraocular pressure play a synergistic role in the progression of glaucoma. The study found that CH can change with changes in basic intraocular pressure, means CH increases when intraocular pressure decreases, while the CH decreases conversely when intraocular pressure increases. Most clinical case studies have shown a decrease in CH after LASER refractive surgery. CH has its limitations, such as corneal damage or corneal surgery, but in general, CH is a risk factor for glaucoma progression., Conclusion: CH is used as a predictor of glaucoma risk and may help to assess the effect of corneal thickness on intraocular pressure. The clinical significance of CH in the diagnosis and efficacy of glaucoma will become more explicit. In the future, CH can also play an important role in the diagnosis and treatment of glaucoma.

Purpose: Corneal hysteresis (CH) is a corneal biomechanical property measured by the ocular response analyzer (ORA). It is associated with primary open-angle glaucoma development, progression, and severity as well as intraocular pressure (IOP) measurement. Decreases in CH and changes in IOP measurements have been described for laser-assisted refractive surgery; however, patients with prior radial keratotomy (RK) have not been examined. We have performed a cohort study examining CH and intraocular pressure measurements (Goldmann applanation and ORA values including Goldmann-correlated and cornea-compensated IOP [adjusted for corneal hysteresis]) in RK patients and myopic controls with POAG., Methods: Eighty POAG patients (28 RK and 52 myopic controls) were recruited. Central corneal thickness (CCT), prostaglandin analogue (PGA) use, perimetric stage, and history of cataract and glaucoma filtration surgery were assessed through chart review. Participants underwent testing with the ORA (yielding measures of CH, cornea-compensated [IOPcc], Goldmann-correlated IOP [IOPgc], and corneal resistance factor [CRF]), Goldmann applanation, A-scan for axial length (AL), and corneal topography. Slit lamp exam was performed to assess for number of incisions in RK patients., Results: Adjusting for AL and CCT, CH was significantly lower in the RK group with an estimated difference of 0.8585 mmHg (p = 0.0112). Cornea-compensated intraocular pressure was significantly higher in the RK group after controlling for Goldmann applanation, AL, and CCT (2.35 mmHg difference, p < 0.001). Corneal resistance factor and IOPgc were not significantly different. A correlational analysis did not reveal a significant correlation between numbers of RK incisions and CH., Conclusions: We report significant differences, with lower CH and higher IOPcc, when comparing eyes with glaucoma and either a history of RK or myopia. These findings may aid in establishing normative decreases in CH with RK and POAG and indicate a possible under-estimation of pressure in RK patients.

Importance: Corneal hysteresis (CH) is a dynamic marker of structural and functional changes in the cornea associated with intraocular pressure (IOP) and central corneal thickness, but its utility in assessing primary angle closure suspects (PACS) has not been fully elucidated., Background: This study assesses if anterior segment measurements correlate with CH in PACS patients., Design: IRB-approved retrospective review of imaging and records at a university practice., Participants: Sixty-three eyes from 37 patients diagnosed as PACS, without other ocular pathology., Methods: Every eye underwent measurements including: ocular response analyzer (ORA), anterior segment optical coherence tomography (OCT) and a clinical evaluation. ORA measurements were correlated with other anatomic parameters using a mixed effects multivariable linear regression framework., Main Outcome Measures: ORA measurements included: CH, corneal resistance factor, Goldmann IOP (IOP g ) and corneal compensated IOP (IOP cc ). Anterior segment OCT measurements included: central corneal thickness (CCT OCT ), nasal and temporal peripheral corneal thicknesses (PCT1 and PCT2), anterior chamber depth (ACD), nasal angle to temporal angle distance (ATA) and temporal and nasal angle measurements. Clinical measurements included: central corneal thickness via pachymetry, IOP measured by Goldmann applanation, axial length by A-scan ultrasound and spherical equivalent., Results: CH was negatively correlated with IOP cc, and ACD CH was positively correlated with CCT OCT , CCT p , CRF, PCT1 and PCT2. Females were found to have lower CH. In multivariable regression controlling for gender, CCT, PCT, IOP and ACD, no correlation was seen between CH and anatomic measurements., Conclusions and Relevance: CH values in PACS do not correlate with anterior segment anatomy., (© 2017 Royal Australian and New Zealand College of Ophthalmologists.)

Purpose: Corneal hysteresis (CH) and corneal resistance factor (CRF) are corneal biomechanical parameters which were measured by ocular response analyzer (ORA). Aim of this study was to define the CH and CRF in high myopic and hyperopic patients and compare the results with emmetropic control group., Methods: A total of 193 eyes of 100 healthy volunteers were included. Study groups were high myopic patients (n = 27) with spherical refractive errors (SRE) of greater than -5.00D, high hyperopic patients (n = 20) with SRE of greater than +3.00D and controls (n = 53) with SRE between ± 1.00D. All subjects underwent IOP and corneal biomechanical evaluation with the ORA. Also Goldmann applanation tonometry (GAT), central corneal thickness (CCT), corneal curvature and axial length measurements were taken., Results: Mean age of groups was 30.7 ± 6.9, 29.1 ± 7.7, 28.9 ± 5.6 years (p > 0.05). Among study groups except CRF and CCT, all parameters were significantly different between study groups. CH was lowest in the high myopic group and highest in the high hyperopia. In all groups, there were significant correlations between CH and CRF, CCT, SRE, SE (spherical equivalent), AL (axial length) and between CRF and CCT. GAT and IOPg (Goldmann-correlated intraocular pressure) measurements were significantly correlated with CCT (p < 0.05). One of the major findings was as the CH approaches 11.2 mmHg, IOPcc (corneal-compensated intraocular pressure) and IOPg get close to each other., Conclusions: The results revealed that CRF is not affected by refractive errors and IOPcc is not affected by any other ocular parameter. The difference between IOPcc and IOPg was greatest in myopic group, and IOP (intraocular pressure) measurement in these patients deserves high suspicion.

Purpose: To investigate the effects of dehydration and fasting on the intraocular pressure (IOP) and corneal biomechanics during Ramadan in healthy subjects., Methods: A total of 36 healthy fasting male volunteers with a mean age of 32.7 ± 5.1 years (range 28-38 years) were enrolled in the study. A Reichert Ocular Response Analyzer (ORA) was used to measure the corneal resistance factor (CRF), corneal hysteresis (CH), Goldman-correlated IOP (IOPg), and corneal-compensated IOP (IOPcc), additionally IOP with Goldmann applanation tonometer (IOP-GAT) was taken. All measurements were recorded at 8:00 am and 4:00 p.m. during Ramadan and during a 1-month follow-up after Ramadan was over., Results: Statistical analysis demonstrated no difference in the ORA measurements including CH, CRF, IOPcc, and IOPg; CCT and CV values between fasting and non-fasting periods or within a single day (diurnal changes). Nine volunteers (25% of total subjects) were excluded because eyedrops were believed to disrupt the Ramadan fast consequently IOP-GAT could not be measured from these subjects. No statistically significant difference was noted between IOP-GAT and IOPg measurements of twenty-seven subjects at the different periods and time points., Conclusions: Our results reveal that fasting during Ramadan does not profoundly affect corneal biomechanics and IOP values in healthy volunteers without ocular diseases such as glaucoma. When planning corneal refractive surgery and determining IOP, the ORA measurements can be done safely during a Ramadan fast. Moreover, ORA may be a better alternative for patients that refuse IOP measurement via GAT for examining the accuracy of IOP during fasting. Further studies are needed to better understand the role of these parameters on corneal disease and glaucoma during fasting.

Purpose: To determine the effect of aging on corneal biomechanical parameters measured via ocular response analyzer in a homogenous healthy Caucasian population., Methods: A total of 2039 Caucasian adults were consecutively recruited and divided into seven groups according to decades of age. The difference in mean corneal hysteresis (CH), mean corneal resistance factor (CRF), mean Goldmann-correlated intraocular pressure (IOPg), and mean corneal-compensated IOP (IOPcc) between decades of age were investigated. The strength of the correlations between corneal biomechanical parameters, and between each biomechanical parameter and age were evaluated. The effect of age on each corneal biomechanical parameter was analyzed., Results: Mean age of the participants (1173 female and 866 male) was 43.30 ± 14.64 years. Mean CH, CRF, IOPcc, and IOPg were 11.49 ± 1.89 mmHg, 11.40 ± 2.30 mmHg, 15.01 ± 3.11 mmHg, and 15.72 ± 3.80 mmHg, respectively. There were significant differences in mean CH, CRF, IOPcc, and IOPg between groups (p < 0.001 for all parameters). There was a significant negative correlation between age and CH (r = -0.067 and p = 0.003), and a significant negative correlation between age and CRF (r = -0.053 and p = 0.017). There was a significant positive correlation between age and IOPg (r = 0.25 and p < 0.001), and between age and IOPcc (r = 0.20 and p < 0.001). Linear regression analysis showed that for every 1-year increase CH decreased 0.011 mmHg, CRF decreased 0.004 mmHg, IOPcc increased 0.053 mmHg, and IOPg increased 0.047 mmHg., Conclusions: Aging can cause significant changes in corneal biomechanical parameters. Corneal biomechanical parameters were correlated with each other, and each was correlated with aging.

Background: We evaluated the relationships between corneal biomechanical properties and structural parameters in patients with newly diagnosed, untreated normal-tension glaucoma (NTG)., Methods: All subjects were evaluated using an Ocular Response Analyzer (ORA) measuring corneal hysteresis (CH) and the corneal resistance factor (CRF). Central corneal thickness (CCT), Goldmann applanation tonometric (GAT) data, axial length, and the spherical equivalent (SE), were also measured. Confocal scanning laser ophthalmoscopy was performed with the aid of a Heidelberg retina tomograph (HRT III). We sought correlations between HRT parameters and different variables including CCT, CH, and the CRF. Multiple linear regression analysis was performed to identify significant associations between corneal biomechanical properties and optic nerve head parameters., Results: We enrolled 95 eyes of 95 NTG patients and 93 eyes of 93 normal subjects. CH and the CRF were significantly lower in more advanced glaucomatous eyes (P = 0.001, P = 0.008, respectively). The rim area, rim volume, linear cup-to-disc ratio (LCDR), and mean retinal nerve fiber layer (RNFL) thickness were significantly worse in more advanced glaucomatous eyes (P < 0.001, P < 0.001, P < 0.001, and P = 0.001). CH was directly associated with rim area, rim volume, and mean RNFL thickness (P = 0.012, P = 0.028, and P = 0.043) and inversely associated with LCDR (P = 0.015), after adjusting for age, axial length, CCT, disc area, GAT data, and SE. However, in normal subjects, there were no significant associations between corneal biomechanical properties and HRT parameters., Conclusions: A lower CH is significantly associated with a smaller rim area and volume, a thinner RNFL, and a larger LCDR, independent of disc size, corneal thickness, intraocular pressure, and age.

Purpose: To examine interrelations between corneal biomechanics, ocular biometric variables and optic disc size (ODS), lamina cribosa depth (LCD) or thickness (LCT) in a healthy population., Material and Methods: In a cross-sectional case-control study, the following measurements were made in 81 eyes of 81 participants: axial length, anterior chamber depth, lens thickness, and central corneal thickness using the optical biometer Lenstar LS900; and corneal hysteresis (CH), corneal resistance factor (CRF), Goldman-correlated intraocular pressure (IOPg), and corneal-compensated IOP (IOPcc) using the Ocular Response Analyzer. Serial horizontal enhanced depth imaging optical coherence tomography (EDI OCT) B-scans of the optic nerve head were obtained in each participant. Mean ODS, mean LCD, and mean LCT were measured in 11 equally spaced horizontal B-scans, excluding the LC insertion area under Bruch's membrane and scleral rim., Results: LCD was measured in 74 of 81 eyes (91.36%); LCT in 60/81 (75.3%); ODS in 81/81 (100%). CRF was poorly, but significantly, correlated with LCT (Pearson's R = 0.264; P = 0.045). IOPcc, IOPg, CH, and ocular biometrics variables were poorly (non-significantly) correlated with LCD, LCT, and ODS., Conclusions: CRF was poorly but directly correlated with LCT. No association was detected between CH or ocular biometric variables and ODS, LCD, or LCT.

Purpose: The aim of this study was to evaluate the corneal biomechanical parameters in patients with ankylosing spondylitis (AS) and to compare them with the healthy subjects., Methods: Sixty patients with AS (study group) and 60 healthy subjects (control group) were enrolled in this prospective study. The study group was further classified as active (n:30) and inactive (n:30). After detailed ophthalmological examination including intraocular pressure (IOP) measurement with Goldmann applanation tonometer (IOPGAT), corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated IOP (IOPcc), and Goldmann-correlated IOP (IOPg) were measured with the Reichert Ocular Response Analyzer (ORA). Central corneal thickness (CCT) was measured with the Spectral-Domain Optical Coherence Tomography (SD-OCT)., Results: The study group's mean CH, CCT, IOPg, and IOPGAT values were lower than the control group (p < 0.05 for all variables). The mean CH, CRF, CCT, IOPg, and IOPGAT values were higher in active patients when compared to the inactive ones (p < 0.001, p < 0.001, p = 0.013, p = 0.021, and p = 0.002, respectively)., Conclusions: AS patients have lower CCT, CH, IOPg, and IOPGAT when compared with healthy subjects. In the active stage of AS, patients present with higher levels of corneal biomechanical parameters with thicker corneas. IOPcc is a more accurate measurement than IOPGAT or IOPg in AS patients.

The purpose of this study is to compare the corneal biomechanical properties in primary hyperparathyroid patients and healthy control subjects. The study consisted of 31 patients with primary hyperparathyroidism (study group) and 31 healthy subjects (control group). Corneal biomechanical properties, including corneal hysteresis (CH), corneal resistance factor (CRF), and intraocular pressure (IOP) were measured with an ocular response analyzer (ORA). IOP was also measured using Goldmann applanation tonometry (GAT), and central corneal thickness (CCT) was measured with an ultrasonic pachymeter. The differences in ORA parameters and CCT between study and control group participants were analyzed. The mean CH in study and control groups was 8.7 ± 1.9 mmHg (5.3-13.7 mmHg) and 9.8 ± 1.5 mmHg (7.7-14.3 mmHg), respectively (p = 0.018). The mean CRF was 9.5 ± 1.8 (5.5-13.7) in the study group compared with 9.8 ± 1.5 (6.2-12.8) in the control group. The difference for CRF was not statistically significant (p = 0.41). In study and control group, corneal-compensated IOP (IOPcc) values were 18.2 ± 4.2 and 16.9 ± 2.7 mmHg, respectively (p = 0.12). Mean IOP measurement values with GAT were 16.3 ± 3.4 mmHg for study group and 16.5 ± 2.7 mmHg for control group (p = 0.71). The mean differences of IOPcc and IOPGAT in the study group eyes were higher than that of control group eyes (1.9 vs. 0.4 mmHg). CCT was 536.5 ± 25.4 µm (490-593 µm) in study group eyes compared with 534.2 ± 31.4 µm (472-602 µm) in control eyes (p = 0.75). Hyperparathyroidism could be associated with a decrease of CH. The differences between IOPcc and IOPGAT in these patients were higher than normal subjects. Underestimation of IOP readings with GAT may be a consequence of the lower CH in patients with hyperparathyroididsm.

Purpose: To compare the diagnostic value of ocular blood flow parameters and choroidal thickness (CT) with standard structural parameters for early glaucoma detection., Methods: A total of 32 patients with pre-perimetric glaucoma were compared with 30 age-matched normal subjects. The thickness of the ganglion cell complex (GCC), retinal nerve fiber layer (RNFL), and the choroid and foveal loss volume (FLV) were measured by means of optical coherence tomography (OCT). Retrobulbar blood velocities (Color Doppler Imaging), corneal compensated intraocular pressure (IOPcc), and corneal hysteresis (CH) were also evaluated. Mean ocular perfusion pressure (MOPP) was calculated by measuring IOP and mean arterial blood pressure as MOPP = ([2/3 diastolic BP + 1/3 systolic BP] × 2/3-IOP). The value of each diagnostic indicator (z-value) was calculated using the Wilcoxon-Mann-Whitney test and the area under the receiver operating characteristic curve (AUC)., Results: The following indicators had the largest AUC and diagnostic value (z-value): mean blood flow velocity in the vortex veins (AUC 1.0; z-value 5.35) and central retinal vein (0.85; 3.74), diastolic blood flow velocity in the central retinal artery (0.73; 2.74) and lateral short posterior ciliary arteries (0.71; 2.53), IOPcc (0.74; -2.9), CH (0.69; 2.24), CT (0.69; -2.28), GCC (0.67; 2.05), and FLV (0.66; -1.86) to discriminate pre-perimetric glaucoma from healthy subjects., Conclusions: Interestingly, ocular hemodynamic parameters performed better than structural parameters in detecting early glaucoma. This highlights the potential of techniques to measure ocular blood flow in glaucoma diagnostics independently of the question whether perfusion abnormalities are a cause or a consequence of the disease.

Rosacea is a chronic cutaneous disorder which is known to cause inflammation and increased proteolytic activity on the ocular surface that might lead to corneal biomechanical alterations. The aim of this study is to evaluate the corneal biomechanical properties of ocular rosacea patients and compare the measurements with healthy individuals as measured with Reichert ocular response analyser (ORA). Besides full eye examination [best corrected visual acuity (BCVA), intraocular pressure (IOP) measured with Goldmann applanation tonometry (IOP-G)], central corneal thickness (CCT), and ORA [corneal hysteresis (CH), corneal resistance factor (CRF), corneal compensated IOP (IOPcc), Goldmann correlated IOP (IOPg)] measurements of 30 eyes of 15 ocular rosacea patients (study group) and 30 eyes of 15 healthy individuals (control group) were performed. For comparisons paired t test was used. Mean age of study group was 45.26 ± 11.65 (range 25 and 63) and control group was 45.00 ± 8.91 (range 26 and 58) years (p = 0.865). No significant difference in BCVA, CCT, IOP-G, IOPcc was detected among groups. However, IOPg, CH, and CRF in the study group were significantly lower than in the control group (p = 0.013, p = 0.013, p = 0.009, respectively). IOPg, CH, and CRF parameters of ocular rosacea patients were significantly lower than normal individuals. These differences and their probable clinical reflections that might effect making decisions in conditions such as glaucoma should be investigated in larger number of patients.

Aim: To determine the effect of drug-induced stress-relief tests on biomechanical properties of the ocular fibrous tunic in eyes with early, moderate, or advanced primary open-angle glaucoma (POAG)., Material and Methods: A total of 202 eyes of 150 patients with POAG of different severity (early, moderate, or advanced) and 36 eyes of 30 healthy controls were examined. The mean patient age was 62±8.2 years. All groups were standardized by age, sex, and the range of corneal-compensated intraocular pressure (IOP) at baseline (21-30 mmHg). All patients underwent a standard ophthalmic examination, including visometry, biomicroscopy, gonioscopy, ophthalmoscopy, and Humphrey visual field assessment. Corneal hysteresis (CH), corneal resistance factor (CRF), CH-CRF difference, corneal-compensated IOP (IOPcc), and Goldmann-related IOP (IOPg) were measured with Ocular Response Analyzer (ORA, Reichert, USA). The axial eye length was measured on an ultrasonic A-scan (Ocuscan RxP, Alcon, USA) in the 10 MHz mode., Results: CH and CRF variability analysis was conducted to assess changes in biomechanical properties of the fibrous tunic due to an IOP decrease and a tendency toward compensation. For the first time, the ratio between CH and CRF changes (ΔCH/ΔCRF) was used to evaluate biomechanical properties of the fibrous tunic. This ratio provides understanding of the significance of CH and CRF changes after reduction of IOP. In early glaucoma patients, it differed inconsiderably from the control group (p>0.05) and averaged 1.62±0.9. In moderate glaucoma, CH changes were more pronounced than those of CRF: ΔCH/ΔCRF - 2.03±2.41 (under conservative treatment) and 2.12±1.07 (without treatment). In advanced glaucoma an opposite pattern was observed: the CH/CRF ratio got closer to 1.0 largely due to CRF changes, while CH changes became much less pronounced (or even negative, in some cases): ΔCH/ΔCRF - 0.27±0.32 (under conservative treatment), 0.16±1.29 (without treatment)., Conclusion: While the IOP decreased as a result of drug-induced stress-relief tests, CH and CRF changes differed between the groups depending on the stage of POAG. In early and moderate glaucoma, CH undergoes greater changes than CRF. In advanced glaucoma, CRF changes are more pronounced, and, hence, the ΔCH/ΔCRF ratio shifts reliably as glaucoma progresses. The ratio has also been shown to depend on the duration of the disease and on whether or not eye drops were prescribed.

Purpose: To evaluate the effect of selective laser trabeculoplasty (SLT) on ocular biomechanics as measured with the ocular response analyzer (ORA, AMETEK Inc. and Reichert Inc.)., Methods: In a prospective case series, 52 eyes of 52 patients (aged 66.6 ± 9.6 years) with insufficient intraocular pressure (IOP) control despite maximum tolerated medical therapy underwent SLT (Solo(™) SLT, Ellex Inc.) for further IOP reduction. Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH) and the corneal resistance factor (CRF) were measured with the ORA prior to and at least 4 weeks following SLT., Results: IOPg decreased statistically significantly from 18.0 ± 6.4 to 14.8 ± 3.8 mmHg and IOPcc from 20.2 ± 6.5 to 16.7 ± 3.4 mmHg (p < 0.001). CH increased from 8.53 ± 2.03 to 9.12 ± 1.83 mmHg (p = 0.028) and CRF decreased from 9.58 ± 2.18 to 9.1 ± 2.1 mmHg (p = 0.037), which was statistically significant. Correcting the CH and CRF data for the influence of IOP reduction with a covariance analysis, however, resulted in an unchanged CH (IOPg adjusted: p = 0.318; IOPcc adjusted: p = 0.468) and CRF (IOPg adjusted: p = 0.320; IOPcc adjusted: p = 0.464) after SLT., Conclusion: Selective laser trabeculoplasty does not change corneal biomechanical properties as measured with the ORA in already pretreated patients with glaucoma. The measured increase in CH and decrease in CRF can be solely explained by IOP reduction., (© 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Purpose: To measure the differences in corneal hysteresis (CH) and corneal resistance factor (CRF) in primary congenital glaucoma (PCG) and in control subjects using ocular response analyser (ORA) and also to compare intraocular pressure (IOP) measurements given by ORA against IOP given by Perkins tonometer, a handheld version of Goldman applanation tonometer (GAT), to determine correlation., Methods: One hundred and eighteen eyes of 78 patients with PCG (group I) and 103 eyes of 53 controls (group II) were evaluated using ORA. In all participants, IOP was measured using the Perkins tonometer. The ORA device uses applanation pressure peaks to generate the corneal-compensated IOP (IOPcc), which is reportedly independent of corneal thickness, and the measurement of Goldman-correlated IOP (IOPg), which is influenced by corneal thickness., Results: The measures in group I were as follows: IOPcc 20.92 ± 5.33; IOPg 18.87 ± 6.67; CH 8.51 ± 2.25; CRF 9.85 ± 3.03; and IOP measured by Goldman 18.32 ± 5.13. The measures in group II were as follows: IOPcc 14.33 ± 2.91; IOPg 14.77 ± 3.00; CH 11.37 ± 1.61; CRF 11.02 ± 1.74; and IOP measured by Goldman 13.74 ± 2.42. The differences of all parameters compared between both groups were statistically significant (p < 0.001 for CH and for all IOP measures and p = 0.001 for CRF). The values of IOPcc, IOPg and IOP measured with Goldman were higher in group I than the values in group II. However, CH and CRF values were lower in group I., Conclusion: A decrease in CH and CRF has been observed in patients with PCG compared to controls. Future research should assess how these parameters are modified in PCG and whether they could provide more information about progression., (© 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Purpose: To evaluate the influence of pterygium on corneal biomechanical properties as measured by the ocular response analyzer (ORA)., Methods: ORA measurements of 48 eyes with primary nasal pterygium were compared with those of healthy fellow eyes. The mean age of the patients was 46.6 ± 18.9 years. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated IOP (IOPcc) were obtained for each subject by using the ORA (Reichert Ophthalmic Instruments, Depew, NY)., Results: CH and CRF were significantly lower in the eyes with pterygium than in the healthy fellow eyes (p1 = 0.011, p2 = 0.014, respectively). On the other hand, there were no significant differences between the eyes with pterygium and healthy fellow eyes concerning IOPg and IOPcc (p1 = 0.948, p2 = 0.129, respectively)., Conclusions: The present study showed that biomechanical properties measured by ORA were affected by pterygium. The eyes with primary nasal pterygium had lower CH and CRF than healthy fellow eyes. Therefore, the effect of pterygium should be taken into account in order to make correct diagnoses by ORA.

Purpose: The purpose was to investigate a possible association of corneal hysteresis (CH) and corneal resistance factor (CRF) with open-angle glaucoma and the severity of disease., Methods: In this prospective cross-sectional study we recruited 86 open-angle glaucoma patients, 16 patients with ocular hypertension (OHT,) and 44 age-matched controls. Each participant had a complete glaucoma workup including measurements with the Ocular Response Analyzer and computerized perimetry with the Humphrey 30-2 SITA Standard program. Visual field damage was based on mean deviation (MD) and considered as early glaucomatous with a MD > - 6 dB, moderate glaucomatous between -6 and -12 dB and advanced glaucomatous < -12 dB. The association between ORA parameters, glaucoma, and disease severity was evaluated using univariate and multivariate linear regression analyses., Results: There was a statistically significant correlation between the biomechanical parameters and intraocular pressure, central corneal thickness, axial length, and age. On average, glaucoma patients had the lowest adjusted CH (8.96 ± 1.43 mmHg) and CRF (9.07 ± 1.93 mmHg) values in comparison to OHT patients (CH: 10.2 ± 1.5 mmHg; CRF: 10.6 ± 2.1 mmHg) and controls (CH: 9.7 ± 1.4 mmHg; CRF: 10.2 ± 1.9 mmHg). This difference was statistically significant (CH: p = 0.003; CRF: p = 0.008). There was also a statistically significant difference in adjusted CH (p = 0.001) and CRF (p = 0.004) values between the controls and the visual field groups, with the lowest values being in the most advanced group., Conclusions: Before interpreting corneal biomechanical parameters, it seems important to adjust the measured data for their underlying influencing factors. Glaucoma patients with lower adjusted CH and CRF probably have more advanced disease and should, therefore, be treated more aggressively and monitored more carefully and frequently.

Purpose: The aim of this study was to investigate the possibility of a relationship between corneal biomechanical properties and different grades of dermatochalasis., Patients and Methods: Patients were assigned to four groups according to the severity of their dermatochalasis: normal (Group 1), mild (Group 2), moderate (Group 3), and severe (Group 4). An Ocular Response Analyzer device was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), and corneal-compensated intraocular pressure (IOPcc)., Results: We found no significant differences in the mean values of the CH, CRF, and IOPcc of all groups (P=0.75, P=0.93, and P=0.11, respectively). However, CH and IOPcc were negatively correlated in Group 1, Group 2, and Group 3 patients (P=0.013, r=-0.49; P=0.015, r=-0.52; and P=0.011, r=-0.47, respectively), but this correlation was not apparent in the Group 4 patients (P=0.57, r=0.12). CRF and IOPcc were correlated, but only in Group 4 (P=0.001, r=0.66)., Conclusion: Severe dermatochalasis was associated with altered corneal biomechanical properties. Some of the important visual consequences of dermatochalasis and related diseases (such as floppy eyelid syndrome) can be understood by considering corneal biomechanical alterations.

Background: The aim was to evaluate the effects of the Valsalva manoeuvre on Ocular Response Analyzer (ORA) measurements., Methods: A total of 152 eyes of 76 healthy individuals were included. The biomechanical properties of cornea, including corneal hysteresis (CH), corneal resistance factor (CRF) and intraocular pressure (IOP) parameters, namely, cornea compensated IOP (IOPcc) and Goldmann correlated IOP (IOPg) as measured with ORA were obtained before and during the Valsalva manoeuvre. Wilcoxon test for group analysis, Mann-Whitney test for intergroup analysis, Generalized Estimating Equation, and Spearman's test for correlation analysis were used., Results: The mean age of the 76 subjects (52 female) was 34.18 ± 10.20 years (range, 21 to 58 years). The mean IOPcc was 14.50 ± 0.30 mmHg before and 19.80 ± 0.60 mmHg during the Valsalva manoeuvre (p < 0.001). The mean IOPg before the Valsalva manoeuvre was 15.02 ± 0.33 mmHg and during was 20.18 ± 0.63 mmHg (p < 0.001). The mean corneal hysteresis was 11.40 ± 0.15 mmHg before Valsalva manoeuvre, and 10.60 ± 0.16 mmHg during Valsalva manoeuvre (p < 0.001). Pre-Valsalva manoeuvre mean corneal resistance factor was 11.97 ± 0.16 mmHg, whereas during the Valsalva manoeuvre, the mean corneal resistance factor was 12.06 ± 0.20 mmHg (p < 0.001). There was no correlation between age and either pre- or during-Valsalva manoeuvre measurements. The change in IOPcc and corneal hysteresis before and during Valsalva manoeuvre showed no intersexual difference; however, IOPg and corneal resistance factor change before and during Valsalva manoeuvre were significantly higher in male subjects. A negative correlation between pre-Valsalva manoeuvre corneal hysteresis and pre- and during-corneal resistance factor difference (r = -0.167) was detected., Conclusions: Valsalva manoeuvre causes a statistically significant increment in IOPcc, IOPg and corneal resistance factor and statistically significant decrement in corneal hysteresis. For this reason, to obtain reliable results, ORA measurements should be performed in suitable positions and with clothes that do not increase thoracic or abdominal pressure., (© 2015 The Authors. Clinical and Experimental Optometry © 2015 Optometry Australia.)

Background: The aim was to study the relationships between the output parameters of the Ocular Response Analyzer (ORA) and those calculated from the raw ORA data and to ascertain the subject-related variations of ORA parameter calculation procedures., Method: Six subjects were recruited for a prospective study. Up to 32 measurements by ORA were performed in series on the dominant eye of each subject. A relationship was examined between Goldmann-correlated intraocular pressure values (IOPg) obtained from the standard ORA output and IOPg' calculated from raw ORA data with a custom-written procedure. The same analysis was carried out for the parameters of corneal hysteresis (CH and CH'). Data and statistical analysis included Epanechnikov kernel smoothing, orthogonal linear regression, hypothesis testing and bootstrap techniques., Results: The group average (mean ± standard deviation) IOPg and CH values were 11.6 ± 1.8 mmHg and 10.7 ± 1.7 mmHg, respectively. A strong correlation was found between IOPg and IOPg' and also between CH and CH' parameters. There was a significant (Behrens-Fisher test, p < 0.001) difference between subjects for both IOPg and CH calculations, in terms of the regression slope parameter., Conclusions: Subject-related variations of ORA parameter calculation were demonstrated. This could indicate that currently employed estimators of IOP parameters include unreported algorithmic procedures that may lead to biased results., (© 2015 The Authors. Clinical and Experimental Optometry © 2015 Optometry Australia.)

Aim: This study aims to investigate the corneal biomechanical properties of steroid sensitive refractive surgery patients and to compare these with those patients that did not have steroid induced ocular hypertension after refractive surgery., Material and Methods: This retrospective study in a tertiary care center involved 48 eyes with steroid induced ocular hypertension (Group I) and 61 eyes of age and sex matched refractive patients who used topical steroids for the same duration as group I without developing ocular hypertension (group II). All patients had preoperative ophthalmological examination, pachymetry and postoperative corneal hysteresis (CH) and resistance factor (CRF) measurements by ocular response analyser. The preoperative CH and CRF measurements of the two groups were compared., Results: The mean CH was statistically lower in group I (6.89±1.62) as compared to group II (7.80±1.30) (p=0.001). The CRF was higher in group I (7.68±2.26) as compared to group II (7.66±1.72) but the difference was not statistically significant (p=0.96). The preoperative spherical refractive error (r=0.43, p=0.00) and postoperative corneal thickness (r=0.58, p=0.001) were moderately correlated with CH., Conclusions: A statistically significant decrease in CH in subjects with steroid induced ocular hypertension is found. Previous studies have revealed an association of low CH with risk of glaucomatous damage of optic nerve. This may imply risk of optic disc damage in this ocular hypertension group if not recognized and treated properly. However the results should be confirmed with larger sample sizes., (Copyright © 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.)

Purpose: To evaluate the relationship between corneal hysteresis (CH) and corneal resistance factor (CRF) with age, central corneal thickness (CCT), corneal curvature (KM), corneal volume (CV), and refractive error in naïve eyes., Methods: 105 healthy subjects (58 male and 47 female) were included in this study. The ages ranged from 19 to 82 years (mean 43.1 ± 15.4 years) and refraction between -11 D and +6 D (mean -0.79 ± 2.95 D). CH and CRF obtained with the Ocular Response Analyzer (ORA) were correlated with age, refractive error, Goldmann Applanation Tonometry (GAT), and with CCT, KM, CV obtained with the Pentacam, and with Corneal-Compensated Intraocular Pressure (IOPcc) and Goldmann-correlated intraocular pressure measurement (IOPg) obtained with ORA. A multivariable mixed effect model was used to evaluate associations among these parameters., Results: CH ranged from 6.9 to 14.6 mmHg (mean 10.26 ± 1.49 mmHg); CRF ranged from 5.8 to 17 mmHg (mean 10.38 ± 1.64 mmHg). Multivariate analysis showed a statistically significant correlation between CH with CCT (p < 0.001), and KM (p < 0.001), and between CRF with CCT (p < 0.001) and GAT (p < 0.001)., Conclusions: Our findings support the hypothesis that CH and CRF are related to the corneal shape and thickness, and show a decrease of CH with age.

The level of intraocular pressure (IOP) is the main known risk factor for the development and progression of glaucomatous optic neuropathy. Despite Goldmann applanation tonometry (GAT) being the gold standard for determining IOP since the last century, its limitations were obvious from the start and include substantial effects of several eye variables such as axial length, curvature, rigidity, and corneal thickness. These limitations have prompted the development of numerous formulas and nomograms designed to compensate for the ocular characteristics effect on GAT, but none of these methods has been entirely satisfactory. Similarly, as a result of efforts to mitigate some of the limitations of conventional tonometry, several new tonometers have appeared on the scene., (© 2015 Elsevier B.V. All rights reserved.)

Purpose: To compare the corneal biomechanical properties of rheumatoid arthritis (RA) patients with those of healthy controls., Methods: Measurements of 39 eyes of 39 RA patients (patient group) were compared with those of 55 eyes of 55 healthy controls (control group). Corneal hysteresis (CH), corneal resistance factor (CRF), intraocular pressure (IOP), and corneal-compensated IOP (IOPcc) were obtained for each subject by the ocular response analyzer (ORA). Corneal thickness (CCT) was measured by ultrasonic pachymeter., Results: CH and CRF were significantly lower in the patient group than in the control group (p1 = 0.002, p2 = 0.019, respectively). The patient group had significantly higher IOPcc values than the control group (p = 0.024). There was no significant differences between the groups concerning CCT and IOP., Conclusions: RA patients had lower CH and CRF, but higher IOPcc values than healthy controls. RA should be considered when the corneal biomechanical properties measured by the ORA are used for diagnoses or therapies.

Purpose: This study compared the measurements of intraocular pressure (IOP) and ocular pulse amplitude (OPA) using the Dynamic Contour Tonometry (DCT) over silicone hydrogel contact lenses of different modulus. Corneal biomechanics were also measured using the Ocular Response Analyzer (ORA)., Methods: Forty-seven young (mean age 22.3 years, standard deviation 1.2 years) subjects had IOP, OPA, corneal hysteresis (CH) and corneal resistance factor (CRF) measured without lens and with two brands of silicone hydrogel contact lenses. Each eye wore one brand followed by another, randomly assigned, and then the lenses switched over. Difference and agreement of IOP and OPA with and without silicone hydrogel contact lens were studied., Results: The right and left eyes had similar corneal curvatures, central corneal thicknesses, IOP, OPA and corneal biomechanics at baseline. No significant difference was found in CH and CRF when they were measured over different contact lenses. IOP demonstrated a greater difference (95% limits of agreement: 2.73mmHg) compared with no lens when it was measured over high modulus silicone hydrogel lenses. Agreement improved over low lens modulus silicone hydrogel lenses (95% limits of agreement: 2.2-2.4mmHg). 95% limits of agreement were within 1.0mmHg for OPA., Conclusions: This study demonstrated the feasibility of DCT over silicone hydrogel lenses. Low lens modulus silicone hydrogel contact lens in situ has no clinical effect on DCT., (Copyright © 2013 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.)

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]

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]

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 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]

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]

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.

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

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 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]