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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]

Background/Objectives: This study aimed to examine the postoperative changes in the corneal biomechanical properties between solo cataract surgery and solo microhook ab interno trabeculotomy (LOT). Methods: This retrospective case–control study included 37 eyes belonging to 26 patients who underwent solo cataract surgery and 37 eyes belonging to 31 patients who underwent solo µLOT. These two groups were matched according to their preoperative intraocular pressure (IOP), axial length (AL), and age. Corneal Visualization Scheimpflug Technology (Corvis ST) was used to obtain four biomechanical parameters representing the corneal stiffness or corneal deformation at the highest concavity, including stiffness parameter A1 (SP-A1), stress–strain index (SSI), peak distance (PD), and deflection amplitude max (DefAmpMax). These parameters were compared preoperatively and 6 months postoperatively, and between the two surgical groups. Results: Preoperatively, the patients' IOP, age, and AL, as well as their results in four Corvis ST parameters, were similar between the two groups (p > 0.05). No significant difference was observed in SP-A1; however, PD and DefAmpMax were significantly larger, and SSI was significantly smaller postoperatively in the LOT group than in the cataract group. Conclusions: Corneal stiffness was reduced, and the cornea was more deformed with LOT than cataract surgery. [ABSTRACT FROM AUTHOR]

Corneal biomechanics is a hot topic in ophthalmology. The biomechanical properties (BMPs) of the cornea have important implications in the management and diagnosis of corneal diseases such as ectasia and keratoconus. In addition, the characterization of BMPs is crucial to model the predictability of a corneal surgery intervention, the outcomes of refractive surgery or the follow-up of corneal diseases. The biomechanical behavior of the cornea is governed by viscoelastic properties that allow, among other structural implications, the damping of excess intraocular pressure and the reduction of damage to the optic nerve. Currently, the most versatile and complete methods to measure corneal viscoelasticity are based on air-puff corneal applanation. However, these methods lack the ability to directly measure corneal viscosity. The aim of this work is to propose a new methodology based on the analysis of corneal air-puff measurements through the standard linear solid model (SLSM) to provide analytical expressions to separately calculate the elastic and time-dependent (corneal retardation time and viscosity) properties. The results show the mean values of elasticity (E), viscosity (Ƞ) and corneal retardation time (τ) in a sample of 200 young and healthy subjects. The influence of elasticity and viscosity on viscoelasticity, high-order corneal aberrations and optical transparency is investigated. Finally, the SLSM fed back from experimental E and Ƞ values is employed to compare the creep relaxation response between a normal, an ocular hypertension patient and an Ortho-K user. Corneal biomechanics is strongly affected by intraocular pressure (IOP); however, corneal hysteresis (CH) analysis is not enough to be employed as a risk factor of glaucoma progression. Low values of CH can be accompanied by high or low corneal elasticity and viscosity depending on the IOP threshold from which the time-dependent biomechanical properties trends are reversed. [ABSTRACT FROM AUTHOR]

Allergic conjunctivitis (AC) comprises a group of conditions triggered by environmental allergens, substantially diminishing the quality of life, particularly among children and adolescents. The mechanical impact of eye rubbing in patients with AC is known to induce biomechanical alterations in the cornea. Modern instruments enable the detection and quantification of these corneal biomechanical changes. The ocular response analyzer and CorVis ST have become standard tools for assessing corneal biomechanical properties. We conducted a review of studies that have investigated corneal biomechanics in patients with AC using both devices to elucidate the association between corneal biomechanical changes and early ectasia development. Our analysis highlights significant findings regarding the tomographic biomechanical index parameter in corneal biomechanics among patients with AC. These findings underscore the importance of ocular screening for all patients to promptly detect subclinical keratoconus changes, thereby improving disease management and outcomes.

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.

Purpose: To study the correlation of corneal topography, corneal biomechanical properties, and ocular aberrations with the magnitude of refractive error in myopic eyes. Methods: All myopic patients attending the clinic for refractive surgery were recruited. Data recorded included visual acuity, axial length (AL), central corneal thickness (CCT), manifest refraction spherical equivalent (MRSE), topography (Pentacam - Oculus), corneal biomechanical factors [ocular response analyzer (ORA)], and optical aberrations (iTrace). They were further categorized into group 1 (suitable for femto-LASIK) and group 2 (unsuitable for femto-LASIK). Results: Sixty eyes (30 myopes) of mean age 22.78 ± 2.71 years were enrolled. A negative correlation of refractive error was noted with AL (ρ = -0.9; P < 0.001), total aberrations (ρ = 0.53; P < 0.001), and lower-order aberrations (LOA) (ρ = 0.54; P < 0.001). A strongly positive correlation was noted between CCT and corneal hysteresis (CH) (ρ = 0.63; P < 0.001), CCT and CRF (ρ = 0.56; P < 0.001), CH and corneal resistance factor (CRF) (ρ = 0.83; P < 0.001), and Goldmann equivalent intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) (ρ = 0.78; P < 0.001). An increase in higher-order aberrations (HOAs) as well as lower-order aberrations (LOAs) was noted with increasing sim-K [HOA (r = 0.73, P = 0.001); LOA (r = 0.601, P = 0.014)] and increasing CRF [HOA (r = 0.5, P = 0.006); LOA (r = 0.732, P = 0.001)] in group 2. The amount of refractive error, axial length, central corneal thickness, and sim-K were significantly different in the two groups. Conclusion: Increasing degree of myopia is associated with an increase in axial length, total aberrations, and lower-order aberrations. Corneal biomechanical parameters have a strong correlation with each other. Lower corneal biomechanics are noted in high myopes as they have weaker and thinner corneas. Corneal biomechanics and ocular aberrations do not differ significantly between cases suitable for femto-LASIK and cases unsuitable for femto-LASIK. [ABSTRACT FROM AUTHOR]

Keratoconus (KC), a leading cause of vision impairment, has an unclear aetiology. This study used Mendelian randomization (MR) to explore the causal links between various factors (smoking, asthma, Down syndrome, inflammatory bowel disease, atopic dermatitis, and serum 25-hydroxyvitamin D levels) and KC. A two-sample MR design, grounded in genome-wide association study (GWAS) summary statistics, was adopted using data from FinnGen, UK Biobank, and other GWAS-related articles. The inverse-variance weighted (IVW) method was employed, complemented by the Wald ratio method for factors with only one single-nucleotide polymorphism (SNP). Sensitivity and stability were assessed through Cochrane's Q test, the MR-Egger intercept test, MR-PRESSO outlier test, and the leave-one-out analysis. The IVW results for the ORA (Ocular Response Analyzer) biomechanical parameters indicated significant associations between tobacco smoking (CH: p < 0.001; CRF: p = 0.009) and inflammatory bowel disease (CH: p = 0.032; CRF: p = 0.001) and corneal biomechanics. The Wald ratio method showed tobacco smoking was associated with a lower risk of KC (p = 0.024). Conversely, asthma (p = 0.009), atopic dermatitis (p = 0.012), inflammatory bowel disease (p = 0.017), and serum 25-hydroxyvitamin D levels (p = 0.039) were associated with a higher risk of KC by IVW, and the same applied to Down syndrome (p = 0.004) using the Wald ratio. These results underscore the role of corneal biomechanics as potential mediators in KC risk, warranting further investigation using Corvis ST and Brillouin microscopy. The findings emphasise the importance of timely screening for specific populations in KC prevention and management. [ABSTRACT FROM AUTHOR]

Purpose: To study the correlation of corneal topography, corneal biomechanical properties, and ocular aberrations with the magnitude of refractive error in myopic eyes. Methods: All myopic patients attending the clinic for refractive surgery were recruited. Data recorded included visual acuity, axial length (AL), central corneal thickness (CCT), manifest refraction spherical equivalent (MRSE), topography (Pentacam – Oculus), corneal biomechanical factors [ocular response analyzer (ORA)], and optical aberrations (iTrace). They were further categorized into group 1 (suitable for femto-LASIK) and group 2 (unsuitable for femto-LASIK). Results: Sixty eyes (30 myopes) of mean age 22.78 ± 2.71 years were enrolled. A negative correlation of refractive error was noted with AL (ρ = −0.9; P < 0.001), total aberrations (ρ = 0.53; P < 0.001), and lower-order aberrations (LOA) (ρ = 0.54; P < 0.001). A strongly positive correlation was noted between CCT and corneal hysteresis (CH) (ρ = 0.63; P < 0.001), CCT and CRF (ρ = 0.56; P < 0.001), CH and corneal resistance factor (CRF) (ρ = 0.83; P < 0.001), and Goldmann equivalent intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) (ρ = 0.78; P < 0.001). An increase in higher-order aberrations (HOAs) as well as lower-order aberrations (LOAs) was noted with increasing sim-K [HOA (r = 0.73, P = 0.001); LOA (r = 0.601, P = 0.014)] and increasing CRF [HOA (r = 0.5, P = 0.006); LOA (r = 0.732, P = 0.001)] in group 2. The amount of refractive error, axial length, central corneal thickness, and sim-K were significantly different in the two groups. Conclusion: Increasing degree of myopia is associated with an increase in axial length, total aberrations, and lower-order aberrations. Corneal biomechanical parameters have a strong correlation with each other. Lower corneal biomechanics are noted in high myopes as they have weaker and thinner corneas. Corneal biomechanics and ocular aberrations do not differ significantly between cases suitable for femto-LASIK and cases unsuitable for femto-LASIK.

Purpose: Idiopathic normal pressure hydrocephalus (iNPH) is associated with an increased prevalence of open-angle glaucoma, attributed to variations of the pressure gradient between intraocular and intracranial compartments at the level of the lamina cribrosa (LC). As ocular biomechanics influence the behavior of the LC, and a lower corneal hysteresis (CH) has been associated to a higher risk of glaucomatous optic nerve damage, in this study we compared ocular biomechanics of iNPH patients with healthy subjects. Methods: Twenty-four eyes of 24 non-shunted iNPH patients were prospectively recruited. Ocular biomechanical properties were investigated using the ocular response analyzer (Reichert Instruments) for the calculation of the CH, corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated intraocular pressure (IOPcc). Results were compared with those of 25 eyes of 25 healthy subjects. Results: In iNPH eyes, the median CH value and interquartile range (IQR) were 9.7 mmHg (7.8–10) and 10.6 mmHg (9.3–11.3) in healthy controls (p = 0.015). No significant differences were found in IOPcc [18.1 mmHg (14.72–19.92) vs. 16.4 mmHg (13.05–19.6)], IOPg [15.4 mmHg (12.82–19.7) vs. 15.3 mmHg (12.55–17.35)], and CRF [9.65 mmHg (8.07–11.65) vs. 10.3 mmHg (9.3–11.5)] between iNPH patients and controls. Conclusions: In iNPH patients, the CH was significantly lower compared to healthy subjects. This result suggests that ocular biomechanical properties may potentially contribute to the risk of development of glaucomatous optic nerve damage in iNPH patients. [ABSTRACT FROM AUTHOR]

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]

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]

Clinical measurement of corneal biomechanics can aid in the early diagnosis, progression tracking, and treatment evaluation of ocular diseases. Over the past two decades, interdisciplinary collaborations between investigators in optical engineering, analytical biomechanical modeling, and clinical research has expanded our knowledge of corneal biomechanics. These advances have led to innovations in testing methods (ex vivo, and recently, in vivo) across multiple spatial and strain scales. However, in vivo measurement of corneal biomechanics remains a long-standing challenge and is currently an active area of research. Here, we review the existing and emerging approaches for in vivo corneal biomechanics evaluation, which include corneal applanation methods, such as ocular response analyzer (ORA) and corneal visualization Scheimpflug technology (Corvis ST), Brillouin microscopy, and elastography methods, and the emerging field of optical coherence elastography (OCE). We describe the fundamental concepts, analytical methods, and current clinical status for each of these methods. Finally, we discuss open questions for the current state of in vivo biomechanics assessment techniques and requirements for wider use that will further broaden our understanding of corneal biomechanics for the detection and management of ocular diseases, and improve the safety and efficacy of future clinical practice.

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]

Purpose: The purpose of the study was to evaluate Ocular Response Analyzer (ORA) measurements and endothelial cell density (ECD) in patients who received intravitreal dexamethasone implant (Ozurdex®) injection for diabetic macular edema. Methods: Twenty-three eyes of 13 patients who receive intravitreal dexamethasone implant injection (Group 1) for diabetic macular edema and 33 eyes of 33 healthy individuals (Group 2) were included in the study. All participants underwent a complete ophthalmologic examination including intraocular pressure measurement with Goldmann applanation tonometer (IOP-GAT), ORA measurements, and specular microscopy. Results: The mean age of the patients was 65.43±8.20 (49-75) in Group 1 and 61.94±4.52 (56-71) in Group 2 (p=0.114). The mean IOP-GAT was significantly higher in Group 1 (18.22±3.41; range 12-28 mmHg) than in Group 2 (15.41±3.07; range 8-21 mmHg) (p=0.02). The mean ECD was 2632.4±209.6 (2232-3067) cell/mm2 in Group 1 and 2567±206.37 (2140-2854) cell/mm2 in Group 2 (p=0.60). The mean corneal resistance factor (CRF) was 12.16±2.35 (7.4-15.3) mmHg in Group 1 and 10.18±1.83 (6.7-14.2) mmHg in Group 2 (p=0.02). Mean corneal hysteresis (CH) in Groups 1 and 2 was 8.87±2.45 (4.1-13.4) mmHg and 10.47±1.43 (6.9-13.2) mmHg, respectively (p=0.001). Mean corneal compensated IOP and Goldman correlated IOP (IOPg) were higher in Group 1 (24.72±7.12; range 12.1-36.4 mmHg and 23.21±7.01; range 14.2-36.2 mmHg) than in Group 2 (14.95±3.6; range 8.3-22.9 mmHg and 14.33±3.84; range 6.3-21.7 mmHg) (p<0.001). IOP-GAT was correlated with IOPg (p=0.01). Conclusion: Intravitreal Ozurdex® injection effects IOP, while it has no significant effect on ECD. Ozurdex® injections changed corneal biomechanical properties such as CH and CRF. Thus, ORA may be a useful to avoid underestimating the IOP and missing the alteration of elastic properties of the cornea. [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]

Keratoconus (KC), a leading cause of vision impairment, has an unclear aetiology. This study used Mendelian randomization (MR) to explore the causal links between various factors (smoking, asthma, Down syndrome, inflammatory bowel disease, atopic dermatitis, and serum 25-hydroxyvitamin D levels) and KC. A two-sample MR design, grounded in genome-wide association study (GWAS) summary statistics, was adopted using data from FinnGen, UK Biobank, and other GWAS-related articles. The inverse-variance weighted (IVW) method was employed, complemented by the Wald ratio method for factors with only one single-nucleotide polymorphism (SNP). Sensitivity and stability were assessed through Cochrane’s Q test, the MR-Egger intercept test, MR-PRESSO outlier test, and the leave-one-out analysis. The IVW results for the ORA (Ocular Response Analyzer) biomechanical parameters indicated significant associations between tobacco smoking (CH: p < 0.001; CRF: p = 0.009) and inflammatory bowel disease (CH: p = 0.032; CRF: p = 0.001) and corneal biomechanics. The Wald ratio method showed tobacco smoking was associated with a lower risk of KC (p = 0.024). Conversely, asthma (p = 0.009), atopic dermatitis (p = 0.012), inflammatory bowel disease (p = 0.017), and serum 25-hydroxyvitamin D levels (p = 0.039) were associated with a higher risk of KC by IVW, and the same applied to Down syndrome (p = 0.004) using the Wald ratio. These results underscore the role of corneal biomechanics as potential mediators in KC risk, warranting further investigation using Corvis ST and Brillouin microscopy. The findings emphasise the importance of timely screening for specific populations in KC prevention and management.

Abstract Background This study analyzed regional corneal thickness remodeling, biomechanical properties, and visual outcomes after femtosecond laser-assisted in situ keratomileusis combined with intraoperative accelerated corneal collagen crosslinking (LASIK Xtra) for myopia. Methods This retrospective study analyzed 21 consecutive patients (18 women, three men; 42 eyes) who were treated with LASIK Xtra. All treatments were performed with ultraviolet-A (energy, 2.7 J/cm2; irradiance, 30 mW/cm2), using continuous (90 s) illumination. Postoperative values of corneal biometrics and visual outcomes were compared with preoperative values. Corneal thickness changes were evaluated using anterior segment optical coherence tomography. All patients were followed up for 12-month postoperatively. Preoperative and postoperative data were compared statistically using the paired t-test for normally distributed parameters and the Wilcoxon rank-sum test and Friedman analysis of variance with Bonferroni correction for non-normally distributed data. Results Uncorrected distance visual acuity (UDVA) significantly improved at 6-month after surgery (P

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]

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.

Aim The aim of the study was to report on the ocular response analyzer and posterior segment optical coherence tomography findings in refractive surgery candidates. Patients and methods The study was conducted on 100 eyes of 50 (37 females) patients seeking refractive surgery at a private eye center in Alexandria, Egypt. Following detailed history taking, all study participants were subjected to a thorough ophthalmic examination including assessment of uncorrected and best-corrected visual acuity, manifest and cycloplegic refraction, slit-lamp examination, measurement of intraocular pressure (IOP) using Goldmann applanation tonometry, and fundus examination using a high plus auxiliary lens. Optical coherence tomography and corneal biomechanical properties were then studied using the Reichert ocular response analyzer. Results The mean±SD age of the study patients was 25.27±4.9 years and of contact lens wear (24% of study patients) was 2.5±0.9 years. The mean±SD of the manifest refractive error was −5.6±5.2 D sphere and −1.6±1.2 D cylinder and of the best-corrected visual acuity was 0.9±0.2. The mean±SD of the IOPg, IOPcc, corneal hysteresis and cornea resistance factor were 14.9±3.8, 16.5±3.4, 9.3±1.9, and 9.4±2 mmHg, of the Peripapillary Retinal Nerve Fibre Layer (pRNFL) thickness were 68.9±20.5 μ nasal, 113.3±20.7 μ superior, 77.7±16 μ temporal, and 119.3±21.5 μ inferior and of the central macula thickness was 270.8±22.9 μ. Conclusions The corneal biomechanical properties and the macular nerve fiber layer thickness are not correlated with the refractive error of the eye, whereas the peripapillary nerve fiber layer thickness correlates with the refractive error and the visual acuity. Screening of the corneal biomechanical properties and the nerve fiber layers is recommended for refractive surgery candidates.

BACKGROUND: The aim of this study is to analyze and compare the intraocular pressure (IOP) values measured in three different kinds of participants such as healthy subjects (HS), keratoconus patients (KP), and those who underwent myopic photorefractive keratectomy (MPRK). The devices used in this study are the Goldmann Applanation Tonometry (GAT), the dynamic contour tonometry (DCT), the ocular response analyzer (ORA), and the Corvis ST (CST). SUBJECTS AND METHODS: This research included 92 eyes of 92 h, 63 eyes of 63 KP, and 58 eyes of 58 MPRKM. Each participant underwent a complete ophthalmic evaluation and IOP measurement with GAT, DCT, ORA, and CST. A statistical analysis was conducted to detect possible differences and correlations. RESULTS: First, according to the observed data, HS eyes displayed mean IOP values measured with GAT, DCT, ORA, and CST, respectively, 15.82 ± 2.74 mmHg, 17.63 ± 2.28 mmHg, 16.24 ± 3.14 mmHg, and 17.31 ± 3.21 mmHg. Then, KP eyes showed mean IOP values measured with GAT, DCT, ORA, and CST of, respectively, 14.89 ± 1.64 mmHg, 16.97 ± 2.08 mmHg, 13.09 ± 3.12 mmHg, and 13.78 ± 2.11 mmHg. Finally, MPRK eyes showed mean IOP values measured with GAT, DCT, ORA, and CST of, respectively, 13.92 ± 1.34 mmHg, 15.39 ± 2.86 mmHg, 16.63 ± 2.51 mmHg, and 15.06 ± 1.56 mmHg. CONCLUSION: According to the observed data, ORA and GAT might be used interchangeably in HS, whereas GAT, ORA, and CST in KP eyes. Moreover, it has been noticed that in those eyes that previously undergone a myopic PRK, GAT provided lower values of IOP in comparison with other devices.

Aim The aim of the study was to report on the ocular response analyzer and posterior segment optical coherence tomography findings in refractive surgery candidates. Patients and methods The study was conducted on 100 eyes of 50 (37 females) patients seeking refractive surgery at a private eye center in Alexandria, Egypt. Following detailed history taking, all study participants were subjected to a thorough ophthalmic examination including assessment of uncorrected and best-corrected visual acuity, manifest and cycloplegic refraction, slit-lamp examination, measurement of intraocular pressure (IOP) using Goldmann applanation tonometry, and fundus examination using a high plus auxiliary lens. Optical coherence tomography and corneal biomechanical properties were then studied using the Reichert ocular response analyzer. Results The mean±SD age of the study patients was 25.27±4.9 years and of contact lens wear (24% of study patients) was 2.5±0.9 years. The mean±SD of the manifest refractive error was −5.6±5.2 D sphere and −1.6±1.2 D cylinder and of the best-corrected visual acuity was 0.9±0.2. The mean±SD of the IOPg, IOPcc, corneal hysteresis and cornea resistance factor were 14.9±3.8, 16.5±3.4, 9.3±1.9, and 9.4±2 mmHg, of the Peripapillary Retinal Nerve Fibre Layer (pRNFL) thickness were 68.9±20.5 μ nasal, 113.3±20.7 μ superior, 77.7±16 μ temporal, and 119.3±21.5 μ inferior and of the central macula thickness was 270.8±22.9 μ. Conclusions The corneal biomechanical properties and the macular nerve fiber layer thickness are not correlated with the refractive error of the eye, whereas the peripapillary nerve fiber layer thickness correlates with the refractive error and the visual acuity. Screening of the corneal biomechanical properties and the nerve fiber layers is recommended for refractive surgery candidates. [ABSTRACT FROM AUTHOR]

BACKGROUND: The aim of this study is to analyze and compare the intraocular pressure (IOP) values measured in three different kinds of participants such as healthy subjects (HS), keratoconus patients (KP), and those who underwent myopic photorefractive keratectomy (MPRK). The devices used in this study are the Goldmann Applanation Tonometry (GAT), the dynamic contour tonometry (DCT), the ocular response analyzer (ORA), and the Corvis ST (CST). SUBJECTS AND METHODS: This research included 92 eyes of 92 h, 63 eyes of 63 KP, and 58 eyes of 58 MPRKM. Each participant underwent a complete ophthalmic evaluation and IOP measurement with GAT, DCT, ORA, and CST. A statistical analysis was conducted to detect possible differences and correlations. RESULTS: First, according to the observed data, HS eyes displayed mean IOP values measured with GAT, DCT, ORA, and CST, respectively, 15.82 ± 2.74 mmHg, 17.63 ± 2.28 mmHg, 16.24 ± 3.14 mmHg, and 17.31 ± 3.21 mmHg. Then, KP eyes showed mean IOP values measured with GAT, DCT, ORA, and CST of, respectively, 14.89 ± 1.64 mmHg, 16.97 ± 2.08 mmHg, 13.09 ± 3.12 mmHg, and 13.78 ± 2.11 mmHg. Finally, MPRK eyes showed mean IOP values measured with GAT, DCT, ORA, and CST of, respectively, 13.92 ± 1.34 mmHg, 15.39 ± 2.86 mmHg, 16.63 ± 2.51 mmHg, and 15.06 ± 1.56 mmHg. CONCLUSION: According to the observed data, ORA and GAT might be used interchangeably in HS, whereas GAT, ORA, and CST in KP eyes. Moreover, it has been noticed that in those eyes that previously undergone a myopic PRK, GAT provided lower values of IOP in comparison with other devices. [ABSTRACT FROM AUTHOR]

Background: This study analyzed regional corneal thickness remodeling, biomechanical properties, and visual outcomes after femtosecond laser-assisted in situ keratomileusis combined with intraoperative accelerated corneal collagen crosslinking (LASIK Xtra) for myopia.Methods: This retrospective study analyzed 21 consecutive patients (18 women, three men; 42 eyes) who were treated with LASIK Xtra. All treatments were performed with ultraviolet-A (energy, 2.7 J/cm2; irradiance, 30 mW/cm2), using continuous (90 s) illumination. Postoperative values of corneal biometrics and visual outcomes were compared with preoperative values. Corneal thickness changes were evaluated using anterior segment optical coherence tomography. All patients were followed up for 12-month postoperatively. Preoperative and postoperative data were compared statistically using the paired t-test for normally distributed parameters and the Wilcoxon rank-sum test and Friedman analysis of variance with Bonferroni correction for non-normally distributed data.Results: Uncorrected distance visual acuity (UDVA) significantly improved at 6-month after surgery (P < 0.001). The central and inner regional corneal epithelial thickness significantly increased after LASIK Xtra (P < 0.05 for all), while the peripheral corneal epithelial thickness remained stable at 12-month after surgery. There was also a statistically significant decreased in the stromal thickness at most locations (P < 0.05 for all), except in the outer superior and outer superior-temporal regions.Conclusions: LASIK Xtra provided improvement in UDVA, corneal curvature, and corneal biomechanical stability. Because the results of this retrospective study results depended on the cohort members' past information, it was inferred and confirmed that regular corneal thickness remodeling occurred after treatment. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to identify corneal biomechanical parameters measured by ORA in patients with TED compared to the healthy group. The NOSPECS classification of patients is used to assess the relation between biomechanical changes and disease severity. Methods: We included 22 TED patients, diagnosed with TED for more than five years, and 43 healthy participants. The NOSPECS classification was assessed as mild (grade 1-3) and severe (grade 4-6) disease. For each group, corneal hysteresis (CH), corneal resistance factor (CRF), central corneal thickness (CCT), Goldmann-correlated intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) parameters were measured by ORA. Results: The mean age was 38.8±11.6 years for the TED patients and 42.9± 15.58 years for the control group. For TED patients and healthy volunteers, the mean levels of CRF, CH, and CCT were measured as follows: 10.43±2.04 vs 10.28±1.91 mmHg, p=0.67; 10.18±1.81 vs 10.21±1.68 mmHg, p=0.90; 550.31±35.73 vs 545.23±37.91 µm, p=0.47, respectively. These values were not significant between groups, but they were significantly higher in females compared to males in TED patients [CRF;I0.68 (IQR: 9.49-12.14) vs 8.96 (IQR: 8.04-9.92) mmHg, p=0.002, CH; 10.43 (IQR: 9.48-11.25) vs 8.58 (IQR: 7.90-9.95) mmHg, p=0.003 and CCT; 554.25 (IQR: 536.05-579.52) vs 527.40 (IQR: 492.25-545.90) µm, p=0.014]. CRF values were negatively correlated with NOSPECS score (r=-0.317, p=0.036) and significantly higher CRF was observed in mild patients compared to severe disease (11.43 (IQR: 10.14-12.87) vs 9.46 (IQR: 8.75-10.28) mmHg, p=0.008). Conclusion: We found a significant gender effect on corneal biomechanical parameters of TED patients. CRF, CH and CCT values were significantly higher in females compared to males with TED. The clinical severity score of TED showed negative correlation with CRF. CRF value might be a useful parameter in follow-up of TED patients in clinical practice. [ABSTRACT FROM AUTHOR]

Thermography is the method of noninvasive registration of visible image of the own infrared radiation of the human body surface by special devices. The physiological basis of its application in medical diagnostics is the amplification of infrared radiation intensity from pathologic spots that is connected with the enhancement of blood supply and metabolism.Purpose. To study the possibilities of thermography for functional bleb status assessment, for early diagnostics of bleb scarring processes and for definition of needling indications.Patients and methods. There were executed 32 thermography (32 patients and eyes) of blebs in 7 days after minimally invasive sinustrabeculectomy. Authors used thermal imaging Тesto 875-2i with SuperResolution technology and telephoto lens 9°×7°. The bleb area and temperature were studied With IRSoft and Universal Desktop Ruler programs. Intraocular pressure (corneal compensated) (IOPcc) was measured with Ocular Response Analyzer®, ORA.Conclusion. The study has shown the direct correlation dependence between bleb functional activity and its thermographic characteristics (area and temperature).

Purpose: To introduce a new method for estimation of the target intraocular pressure (TIOP) in naïve eyes with early primary open-angle glaucoma (POAG) using corneal hysteresis (CH) and corneal resistance factor (CRF). Methods: A prospective quasi-experimental study was conducted on naïve 90 eyes of 45 patients who were newly diagnosed with early primary open-angle glaucoma (POAG). They were compared to 72 eyes of 36 normal subjects. The TIOP was determined for each eye. The IOP Goldmann (IOPg), IOP corneal-compensated (IOPcc), CH and CRF were estimated by ocular response analyzer (ORA, Reichert) device. Measurements were taken for each patient prior to treatment and after 1, 3, 6, 9 and 12 months of receiving medications; either monotherapy or combination therapy. Results: For all patients, there was a significant negative correlation (p < 0.05) between IOP, either IOPg or IOPcc, and CH, while a significant positive relationship (p < 0.05) existed between IOP and CRF. For patients with early POAG, the CH was significantly increased (p ≤ 0.001), while CRF was significantly decreased (p ≤ 0.001) when TIOP was achieved. At IOP levels higher than TIOP, CH value was lower than CRF with a significant negative correlation between them in contrast to controls. This correlation was reversed on reaching TIOP and CH values became higher than CRF similar to controls. Conclusion: CH, CRF and IOP measured by ORA can be used for TIOP estimation. This provides us with a guide for assessing the effectiveness of medications introduced to patients with POAG. [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.

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AIM: To compare intraocular pressure (IOP) measurements before and after laser in situ keratomileusis (LASIK) with a femtosecond laser for flap creation using ocular response analyzer (ORA) and Goldmann applanation tonometry, and to identify factors that may influence the preoperative and postoperative IOP. METHODS: A prospective study conducted on myopic patients who underwent LASIK using a femtosecond laser for flap fashioning. Enrolled patients were evaluated preoperatively, 6wk and 3mo postoperatively for manifest refraction (MR), keratometric (K) readings and central corneal thickness (CCT) using a scheimpflug-based topography. Corneal resistance factor (CRF), corneal hysteresis (CH), Goldmann correlated IOP (IOPg) and corneal compensated IOP (IOPcc) were measured using ORA besides IOP assessment by Goldman applanation tonometry (GAT). RESULTS: There was a statistically significant decrease in measures of IOPg by 3.35±0.83 mm Hg, followed by GAT which decreased by 2.2±0.44 mm Hg, and the least affected by operation was IOPcc which decreased only by 0.87±0.1 mm Hg after 6wk. After 3mo follow up there was a statistically significant decrease in IOPcc which decreased only by 0.76±0.4 mm Hg, followed by IOP GAT by 1.6±0.5 mm Hg, and the most affected by operation was IOPg which decreased by 2.3±0.3 mm Hg. Correspondingly, there was a statistically significant decrease in CH and CRF after 6wk and 3mo. At 3mo, the preoperative MR and preoperative GAT were prominent significant predictors of the postoperative GAT changes. The prediction equation was subsumed. CONCLUSION: IOP measurements and corneal biomechanical factors reduce significantly after LASIK with a femtosecond laser for flap creation. The IOPcc values are less influenced by changes in corneal properties than IOPg and GAT, indicating that IOPcc may provide the most reliable measurement of IOP after this procedure.

Objectives:To compare anterior segment parameters and biomechanical analysis of the cornea in children with joint hypermobility (JH) and healthy children.Materials and Methods:Cross-sectional case-control study. Fifty eyes of 25 children with JH were compared with 74 eyes of 37 healthy age- and sex-matched controls in terms of refractive, anterior segment topographic, and corneal biomechanical measurements. Axial length (AL) was measured with a Nidek AL-Scan biometry device; corneal-compensated intraocular pressure (IOPcc), Goldmann-correlated IOP (IOPg), corneal hysteresis (CH), and corneal resistance factor (CRF) were measured with a Reichert ocular response analyzer (ORA). Central corneal thickness (CCT), anterior chamber depth (ACD), K1/K2 values, iris diameter, and anterior chamber volume (ACV) were measured with a Sirius topography device.Results:Mean age in the JH group was 10.56±4.03 years, while that of the control group was 11.27±2.59 years (p=0.23). Spherical equivalent was -0.22±1.02 diopter (D) in the JH group and -0.12±1.12 D in the control group (p=0.60); CCT was 23.01±0.82 µm in the JH group and 23.17±0.82 µm in the control group (p=0.33). There were no significant differences between the two groups in terms of age, sex, IOP, IOPcc, IOPg, CH, CRF, AL, K1, K2, iris diameter, ACD, and ACV.Conclusion:JH, which causes increased flexibility of the joints, was concluded not to cause a significant change in the corneal biomechanical markers of CRF and CH or in anterior segment topographic parameters.

Uncontrolled administration and prolonged use of antihypertensive drugs with preservatives often leads not only to subjectively poor tolerance of treatment, but also to a deterioration in the results of subsequent surgery, if required. The manifestations of dry eye syndrome and its aggravation as a result of such drops use can lead the patients to refuse therapy and worsening the prognosis. The manifestations of dry syndrome are often detected before any hypotensive therapy begins, since the functions of secretory cells change with age and there is always the influence of adverse environmental factors. It is necessary to examine the condition of the anterior surface of the eye to resolve the issue of the need to prescribe drugs without preservatives for all patients before the appointment of antihypertensive therapy. However, sometimes it is not possible due to lack of time or equipment. Therefore, it is important to study the condition of the anterior eye surface in patients with newly diagnosed glaucoma before and during treatment with nonpreservative forms of antihypertensive drugs in order to determine the necessity of the first prescription of non-preservative forms of antihypertensive drops to further interpolate its results into practical recommendations. This study revealed that drug treatment of patients with newly diagnosed glaucoma with the drug Timolol-POS® β-blocker on a non-preservative basis along with IOP compensation improves both subjective and objective indicators of the condition of the anterior surface of the eye with maximum effect after 3 months of treatment. This conclusion suggests the importance of the primary appointment for such patients with instillation drops on a preservative basis.

Abstract Background Accurate measurement of intraocular pressure (IOP) after corneal refractive surgery is of great significance to clinic, and comparisons among various IOP measuring instruments are not rare, but there is a lack of unified analysis. Although Goldmann Applanation Tonometer (GAT) is currently the internationally recognized gold standard for IOP measurement, its results are severely affected by central corneal thickness (CCT). Ocular Response Analyzer (ORA) takes certain biomechanical properties of cornea into account and is supposed to be less dependent of CCT. In this study, we conducted the meta-analysis to systematically assess the differences and similarities of IOP values measured by ORA and GAT in patients after corneal refractive surgery from the perspective of evidence-based medicine. Methods The authors searched electronic databases (MEDLINE, EMBASE, Web of science, Cochrane library and Chinese electronic databases of CNKI and Wanfang) from Jan. 2005 to Jan. 2019, studies describing IOP comparisons measured by GAT and ORA after corneal refractive surgery were included. Quality assessment, subgroup analysis, meta-regression analysis and publication bias analysis were applied in succession. Results Among the 273 literatures initially retrieved, 8 literatures (13 groups of data) with a total of 724 eyes were included in the meta-analysis, and all of which were English literatures. In the pooled analysis, the weighted mean difference (WMD) between IOPcc and IOPGAT was 2.67 mmHg (95% CI: 2.20~3.14 mmHg, p mean-∆IOPGAT > mean-∆IOPcc. Conclusions IOPcc, which is less dependent on CCT, may be more close to the true IOP after corneal refractive surgery compared with IOPg and IOPGAT, and the recovery of IOPcc after corneal surface refractive surgery may be more stable than that after lamellar refractive surgery.

Intraocular pressure (IOP) is currently the only modifiable risk factor in glaucoma. Since all our efforts are directed towards maintaining a stable IOP to halt glaucoma progression, proper understanding about the science behind IOP measurement and biomechanics of cornea becomes paramount. In this paper, we address the basics of corneal biomechanics, recent developments and its impact on glaucoma diagnosis and management. An extensive literature search was done using PubMed and Google Scholar with the search terms such as biomechanics, hysteresis, and glaucoma. Relevant articles published in English language were reviewed.

Corneal biomechanical data has been used since 2005 to screen for keratoconus and corneal ectasia by corneal specialists. Older technology uses force applanation techniques over a 3 mm area in the central cornea, making it highly dependent on extraneous variables and unable to calculate the elasticity of the tissue. Brillouin microscopy is a newer method that uses a natural shift in the frequency of light as it passes through a material. This frequency shift can be used to estimate the viscoelasticity of the tissue. The advantage of Brillouin microscopy is that it can create a full three-dimensional (3D) map of the entire cornea without direct contact. A literature search was conducted using the databases PubMed, Google Scholar, and Ovid regarding the applications of Brillouin microscopy in corneal diagnostics. A final total of 16 articles was included describing the various ex vivo and in vivo studies conducted using Brillouin microscopy. Applications of this technology spanned from keratoconus diagnosis to post-corneal refractive surgery evaluation. All studies evaluated corneal biomechanics and other corneal properties through the quantification of Brillouin frequency shifts. Many of the studies found that this diagnostic device is capable of detecting subtle changes in corneal thickness and biomechanics in keratoconic corneas at a high level of specificity and sensitivity. However, limitations of Brillouin microscopy may include the duration of time required for use and fluctuations in accuracy depending on the corneal hydration state. Future technology seems to be geared toward a combination of optical coherence tomography (OCT) and Brillouin microscopy, using OCT as a three-dimensional pupil-tracking modality. Further research and understanding of the technology involved will lead to better care of patients in the field of ophthalmology., Competing Interests: Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Loveless et al.)

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.

Copyright of MN Opthalmology / MN Oftalmoloji is the property of Medical Network and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Purpose: to study a correlation between morphometric parameters of the eye and tonometry data, taking into account viscoelastic properties of the cornea in patients with primary open-angle glaucoma (POAG), as well as in practically healthy individuals using different methods of tonometry. Patients and Methods. Correlations between morphometric parameters of the eye and tonometry data were studied in view of viscoelastic properties of the cornea in 51 patients with POAG who were observed at the “Optimed” Laser Vision Recovery Center in Ufa (99 eyes) and in 31 practically healthy individuals (62 eyes). Various methods of tonometry were used: tonometry according to Maklakov, contactless tonometry, tonometry with the Ocular Response Analyzer (ORA, Reichert Inc., USA), as well as ultrasound echobiometry, pachymetry. Results. The CH and CRF parameters reflecting the biomechanical properties of the corneoscleral membrane of the eye were close in value to each other with a high degree of positive correlation in the control group (ρ = 0.783, p < 0.001), with an average correlation in the group with POAG (ρ = 0.545, p < 0.001). In eyes with POAG, a negative CH correlation of average degree with corneal-compensated IOP (ρ = -0.572, p < 0.001), a negative CRF correlation of moderate degree with IOP by the Maklakov method (ρ = -0.346, p < 0.001) and corneal-compensated IOP with dynamic bi-directional applanation tonometry (ρ = -0.327, p = 0.001), low correlation with IOP using contactless tonometry (ρ = 0.243, p < 0.015) were observed. In the group of patients with POAG, a positive average correlation was found between the central thickness of the cornea and CRF (ρ = 0.398, p < 0.001), and CH (ρ = 0.368, p < 0.001), low correlation with IOP using contactless tonometry (ρ = 0.266, p = 0.008). Conclusion. Correlations of biomechanical properties of the corneoscleral membrane and morphometric parameters of the eye in patients with POAG were revealed using different methods of tonometry. In the group of patients with POAG and in the control group, positive correlations of the central thickness of the cornea with the IOP level in tonometry were determined by the contactless method, as well as with the main ORA parameters reflecting the visco-elastic properties of the fibrous membrane of the eye — the corneal resistance factor, corneal hysteresis.

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

Purpose. To study tonometry parameters features, measured by different methods, taking into account individual morphometric eye parameters and biomechanical properties of the corneoscleral shell in patients with the initial and the advanced stages of primary open angle glaucoma (POAG).Material and methods. 51 patients (99 eyes) aged 48–82, with the initial (45 eyes) and advanced stages (54 eyes) of POAG were examined. The control group consisted of 31 patients (62 eyes) aged 47–83 without ophthalmic pathology. In addition to standard ophthalmologic examination, tonometry was performed using the Ocular Response Analyzer (ORA, Reichert Inc., the USA).Results. The main tonometry parameters of ORA revealed significant differences between POAG patients and the control group. No significant difference in the central corneal thickness (CCT) was found between the POAG and the control group. Patients with I and II stages of glaucoma taken separately showed differences in CCT and tonometry parameters.Conclusion. Dynamic bi-directional applanation tonometry enables to take into account the changes in viscoelastic properties of the corneoscleral eye shell, and definitely has diagnostic advantages in examining patients with various stages of POAG.

Background Biomechanics of the cornea is represented by corneal hysteresis (CH), which is defined as the viscous damping owing to viscoelastic resistance of the cornea to deformation. Aim Assessing intraocular pressure (IOP) and corneal biomechanics alterations after phacoemulsification. Patients and methods Thirty eyes were uneventfully operated on using phacoemulsification. CH, corneal resistant factor (CRF), corneal compensated intraocular pressure (IOPcc), and Goldmann correlated intraocular pressure (IOPg) values were recorded by ocular response analyzer (ORA). Central corneal thickness (CCT) was evaluated using pentacam preoperatively and postoperatively after 1 day, 1 week, and 1 month. Results Patients comprised 22 males and 8 females, with a mean age of 63.8±6.8years. Preoperative mean CCT was 532.4±39.2 µm, mean CH was 9.4±1.7 mmHg, mean CRF was 9.5±2.0 mmHg, mean IOPg was 15.4±3.9 mmHg, and mean IOPcc was 17.1±3.6 mmHg. CCT significantly increased after 1 day and significantly decreased after 1 week, and decreased again after 1 month but remained significantly higher. CH decreased significantly after 1 day and increased to the preoperative values after 1 week and 1 month. CRF significantly increased after 1 day and then decreased significantly after 1 week and remained significantly lower. Both IOPcc and IOPg insignificantly elevated after 1 day, then significantly declined after 1 week, and insignificantly increased after 1 month but was still lower than the preoperative value. CH, CRF, and CCT correlated significantly except for 1 day after surgery. Conclusion Cataract surgery causes corneal structural alterations, changing biomechanical properties and IOP initially. CCT contributes in these parameters, as there is a correlation with CH and CRF.

Purpose: To evaluate the effect of intravitreal bevacizumab (IVB) injection on corneal biomechanical parameters as measured by the ocular response analyzer (ORA) and Corneal Visualization Scheimpflug Technology (CorVis). Methods: In this prospective pilot study, ORA and CorVis parameters were recorded before and after a three-month course of IVB injection therapy in 16 patients in the injected and the contralateral non-injected control eyes. The changes in the recorded parameters in each group and the differences between the two groups were evaluated and compared. Results: None of the changes in ORA parameters were statistically significant in the injected and non-injected groups before and three months after injection, except for corneal resistance factor (CRF) in injected eyes (paired t-test, P = 0.039). The differences in corneal hysteresis (CH) and CRF were not statistically significant between the two groups (P = 0.441 and 0.236, respectively), but significant differences were noted between corneal compensated IOP (IOPcc) and Goldmann-correlated IOP (IOPg) (P = 0.045 and 0.047, respectively). None of the changes in CorVis parameters were statistically significant in the groups before and at the end of study, except for the time of first corneal applanation (TAp1 ms) in the injected group (P = 0.040, paired t-test). Differences in TAp1, length of the second corneal applanation (LAp2 mm), velocity of the second corneal applanation (VAp2 m/s), intraocular pressure (IOP), and central corneal thickness (CCT) also showed borderline significance between the two groups. Conclusion: In this pilot study IVB injection could change CRF, IOPcc, IOPg, and TAP1 as measured by ORA and CorVis.

INTRODUCTION[|]Corneal biomechanical changes were also suspected and investigated after some scleral procedures but not after strabismus surgery. In this study we aimed to evaluate corneal biomechanical changes following strabismus procedures.with ocular responce analyser. [¤]METHODS[|]Methods: This study a retrospective case series. Corneal biomechanical properties were assessed using the Ocular Response Analyzer (ORA, Reichert Inc., Depew, New York, USA) before, and 6 months after the surgery in 67 eyes of 67 patients performing strabismus surgery. Preoperative and postoperative changes in corneal hysteresis (CH) and corneal resistance factor (CRF) outcomes were examined. [¤]RESULTS[|]Results: In the study group were divided Group1 and Group2 for the performed surgery. Preoperative and postoperative CRF were showed statistically significant differences in Group 1 and Group 2. In Group 1 at preoperative the mean CH was 11.7 +- 2.4 mmHg and 12.3 +- 2.5 mmHg at postoperative. The differences were not statistically significant in Group1. [¤]DISCUSSION AND CONCLUSION[|]This is the first study aimed at evaluating the corneal biomechanical changes after strabismus surgery. and CRF were found to statistically significance at 6 month after strabismus surgery. [¤]