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Background： High intraocular pressure （IOP） and low central corneal thickness （CCT） are important validated risk factors for glaucoma, and some studies also have suggested that eyes with more deformable corneas may be in higher risk of the development and worsening of glaucoma. In the present study, we aimed to evaluate the association between corneal biomechanical parameters and asymmetric visual field （VF） damage using a Corvis-ST device in patients with untreated normal tension glaucoma （NTG）. Methods： In this observational, cross-sectional study, 44 newly diagnosed NTG patients were enrolled. Of these, 31 had asymmetric VF damage, which was defined as a 5-point difference between the eyes according to the Advanced Glaucoma Intervention Study scoring system. Corneal biomechanical parameters were obtained using a Corvis-ST device, such as time from start until the first and second applanation is reached （time A 1 and time A2, respectively）, cord length of the first and second applanation （length A 1 and length A2, respectively）, corneal speed during the first and second applanation （velocity A1 and velocity A2, respectively）, time from start until highest concavity is reached （time HC）, maximum amplitude at the apex of highest concavity （def ampl HC）, distance between the two peaks at highest concavity （peak dist HC）, and central concave curvature at its highest concavity （radius HC）. Results： Time A 1 （7.19 q- 0.28 vs. 7.37 ~ 0.41 ms, P = 0.010）, length A 1 （1.73 [ 1.70-1.76] vs. 1.78 [ 1.76-1.79] mm, P = 0.007）, length A2 （1.58 [1.46-1.70] vs. 1.84 [h76-1.92] mm, P 〈 0.001）, peak dist HC （3.53 [3.08-4.00] vs. 4.33 [3.92-4.74] mm, P = 0.010）, and radius HC （6.20 ± 0.69 vs. 6.59 i h 18 mm, P = 0.032） were significantly lower in the worse eyes than in the better eyes, whereas velocity A 1 and def ampl HC were significantly higher （0.156 [0.149-0.163] vs. 0.145 [0.138-0.152] m/s, P= 0.002 and 1.19 ± 0.13 vs. 1.15 ± 0.13 mm, P = 0.005, respectively）. There was no significant difference in time A2, velocity A2, and time HC between the two groups. In addition, no difference was observed in lOP, CCT, and axial length. In the univariate and multivariate analyses, some of the Corvis-ST parameters, including time A1 and def ampl HC, were correlated with known risk factors for glaucoma, and there was also a significant positive correlation between def ampl HC and age. Conclusions： There were differences in dynamic corneal response parameters but not IOP or CCT between the paired eyes of NTG patients with asymmetric VF damage. We suggest that the shape of the cornea is more easily altered in the worse eyes of asymmetric NTG patients.

To compare the corneal biomechanical parameters measured by Corvis ST in subjects with varying degrees of myopia. And the factors that may affect corneal biomechanical properties were also investigated. Participants in this prospective cross-sectional study were classified into three groups according to spherical equivalent (SE) and axial length (AL): Non-myopia (NM, SE > − 0.50 D and AL < 26 mm), Mild-to-moderate myopia (MM, − 6.00 D < SE ≤ − 0.50 D and AL < 26 mm), high myopia (HM, SE ≤ − 6.00 D or AL ≥ 26 mm). Ten corneal biomechanical parameters were finally included. Linear mixed-effects model accounting for using both eyes in the same participant was carried out to evaluate how the corneal biomechanical parameter was influenced by varying degrees of myopia after adjusting for biomechanically corrected intraocular pressure (bIOP) and central corneal thickness (CCT). Further, multiple linear regression was performed to explore the correlation between corneal biomechanical parameter and SE, AL, bIOP or CCT. A total of 304 eyes from 224 healthy myopic subjects were recorded. There were 95 eyes with NM, 122 eyes with MM, and 87 eyes with HM. After adjusting for bIOP and CCT, eyes with high myopia showed shorter highest concavity time (HC-time, p  = 0.025), greater peak distance (PD, p  = 0.001), greater deflection amplitude (DA-Max, p  = 0.002), smaller whole eye movement (WEM-Max, p  < 0.001) and reduced stiffness parameter (SP-A1, p  < 0.001). Multiple regression analysis showed that five parameters (HC-time, p  < 0.001; PD, p  < 0.001; DA-Max, p  = 0.001; WEM-Max, p  < 0.001; and SP-A1, p  < 0.001) of Corvis ST were significantly correlated with AL, and one parameter (Corvis biomechanical index, p  = 0.016) has significant relationship with SE. With the increase of myopia, significant changes in several corneal biomechanical parameters indicated a progressive decrease in corneal stiffness, independent of bIOP and CCT. Corneal biomechanical parameters may be predictors of scleral mechanical strength in high myopia, which has certain application value in clinical management of myopia.

To evaluate and compare corneal biomechanical properties and densitometry in healthy individuals and type 2 diabetic patients, with and without non-proliferative diabetic retinopathy (NPDR), and to investigate potential associations with glycemic control. This prospective, observational study included 61 diabetic patients (30 without DR and 31 with NPDR) and 76 healthy controls. Comprehensive ophthalmic examinations were performed for all participants, including Corvis ST for corneal biomechanical assessment and Scheimpflug-based densitometry. Glycated hemoglobin (HbA1c) and blood glucose levels were recorded in the diabetic group. Patients with proliferative DR were excluded to maintain more homogeneous cohorts. Diabetic patients demonstrated significantly higher stiffness parameters (stress-strain index) and corneal densitometry compared with healthy controls (p<0.001). In subgroup analyses, the tomographic biomechanical index (TBI) was lower among diabetic patients with retinopathy than those without (p=0.036), suggesting an additional impact of retinopathy on corneal biomechanics. Moderate correlations were identified between HbA1c and specific corneal deformation parameters, highlighting the influence of metabolic control on corneal properties. Blood glucose levels exhibited a moderate positive correlation with TBI (p=0.033). Corneal biomechanics and densitometry differ significantly between diabetic patients and healthy controls, with further alterations in those with non-proliferative retinopathy, and these changes may correlate with glycemic control.

Purpose. To conduct a comparative analysis of corneal biomechanical parameters in initial keratoconus in adults and in children and adolescents. Material and methods. 62 patients with keratoconus stage I according to Amsler – Krummeich classification were included in the study: 31 patients younger than 18 years old (group «Children/Adolescents») and 31 patients older than 18 years old (group «Adults»). Standard methods of examination, Scheimpflug tomography (Pentacam HR) and corneal biomechanics analysis (Corvis ST) were used. Corneal stiffness (SPA1), relative thickness according to Ambrosio (ARTh), integrated radius (IR) and deformation coefficient (DA Ratio) were evaluated. Statistical analysis was performed using Student’s t-test. Results. The groups did not differ in clinical and demographic characteristics except for age. Children/adolescents had 4.5% higher corneal thickness at the thinnest point (p<0.001) and 3.2–3.3% lower keratometry (p<0.05). Biomechanical parameters showed significant differences: in children/adolescents, SPA1 was 18.4% lower, IR was 20.6% higher, ARTh was 15.7% higher, and DA Ratio was 7.0% lower (p<0.05). Conclusion. Corneal biomechanical changes in initial keratoconus in children and adolescents are more significant than in adults, emphasizing the need for early diagnosis and monitoring at a young age for timely i ntervention. Key words: keratoconus, corneal biomechanics, children, adolescents, adults, Corvis ST, Scheimpflug tomography, Pentacam, diagnosis.

Investigating the corneal biomechanical characteristics and clinical correlations in children with dust mite-induced perennial allergic conjunctivitis (PAC). This study is a prospective cross-sectional study that enrolled 260 children (aged 6 to 12), divided into the PAC group and the healthy control group (NAC).Corneal biomechanical parameters were measured using the OCULUS Corvis ST, and the Ocular Surface Disease Index (OSDI), Visual Analogue Scale (VAS), typical symptom and sign scores, corneal fluorescein staining(CFS), tear break-up time (TBUT), and tear meniscus height (TMH) were recorded. The PAC group showed higher symptom/sign scores and poorer tear-film function (all p  < 0.001). First applanation time (A1) and first applanation length (AL1) were shorter, and first applanation velocity (A1V) and second applanation time (A2) were higher (all p  < 0.05). After covariate adjustment/weighting, second applanation time (A2), deformation amplitude ratio (DA ratio), and integrated radius (IR) also increased (all p  < 0.05). Symptoms and signs showed weak to moderate correlations with multiple biomechanical parameters. CFS acted as a mediator for differences in some parameters. Cluster analysis revealed a “soft subtype”, and trend analysis suggested that the corneal biomechanical differences in normal children are primarily driven by corneal thickness, with limited age effects. PAC children show reduced corneal stability and biomechanical susceptibility, warranting regular follow-up for early risk stratification.

Background The diagnosis of keratoconus, as the most prevalent corneal ectatic disorder, at the subclinical stage gained great attention due to the increased acceptance of refractive surgeries. This study aimed to assess the pattern of the corneal biomechanical properties derived from Corneal Visualization Scheimpflug Technology (Corvis ST) and evaluate the diagnostic value of these parameters in distinguishing subclinical keratoconus (SKC) from normal eyes. Methods This prospective study was conducted on 73 SKC and 69 normal eyes. Subclinical keratoconus eyes were defined as corneas with no clinical evidence of keratoconus and suspicious topographic and tomographic features. Following a complete ophthalmic examination, topographic and tomographic corneal assessment via Pentacam HR, and corneal biomechanical evaluation utilizing Corvis ST were done. Results Subclinical keratoconus eyes presented significantly higher Deformation Amplitude (DA) ratio, Tomographic Biomechanical Index (TBI), and Corvis Biomechanical Index (CBI) rates than the control group. Conversely, Ambrósio Relational Thickness to the Horizontal profile (ARTh), and Stiffness Parameter at the first Applanation (SPA1) showed significantly lower rates in SKC eyes. In diagnosing SKC from normal eyes, TBI (AUC: 0.858, Cut-off value: > 0.33, Youden index: 0.55), ARTh (AUC: 0.813, Cut-off value: ≤ 488.1, Youden index: 0.58), and CBI (AUC: 0.804, Cut-off value: > 0.47, Youden index: 0.49) appeared as good indicators. Conclusions TBI, CBI, and ARTh parameters could be valuable in distinguishing SKC eyes from normal ones.

PurposeTo assess corneal stiffening of standard (S-CXL) and accelerated (A-CXL) cross-linking protocols by dynamic corneal response parameters and corneal bending stiffness (Kc[mean/linear]) derived from Corvis (CVS) Scheimpflug-based tonometry. These investigations were validated by corneal tensile stiffness (K[ts]), derived from stress-strain extensometry in ex vivo porcine eyes.MethodsSeventy-two fresh-enucleated and de-epithelized porcine eyes were soaked in 0.1% riboflavin solution including 10% dextran for 10 min. The eyes were separated into four groups: controls (n = 18), S-CXL (intensity in mW/cm2*time in min; 3*30) (n = 18), A-CXL (9*10) (n = 18), and A-CXL (18*5) (n = 18), respectively. CXL was performed using CCL Vario. CVS measurements were performed on all eyes. Subsequently, corneal strips were extracted by a double-bladed scalpel and used for stress-strain measurements. K[ts] was calculated from a force-displacement curve. Mean corneal stiffness (Kc[mean]) and constant corneal stiffness (Kc[linear]) were calculated from raw CVS data.ResultsIn CVS, biomechanical effects of cross-linking were shown to have a significantly decreased deflection amplitude as well as integrated radius, an increased IOP, and SP A1 (P < 0.05). Kc[mean]/Kc[linear] were significantly increased after CXL (P < 0.05). In the range from 2 to 6% strain, K[ts] was significantly higher in S-CXL (3*30) compared to A-CXL (9*10), A-CXL (18*5), and controls (P < 0.05). At 8% to 10% strain, all protocols induced a higher stiffness than controls (P < 0.05).ConclusionSeveral CVS parameters and Kc[mean] as well as Kc[linear] verify corneal stiffening effect after CXL on porcine eyes. S-CXL seems to have a higher tendency of stiffening than A-CXL protocols have, which was demonstrated by Scheimpflug-based tonometry and stress-strain extensometry.

Purpose To assess the associations of corneal biomechanical properties as measured by the Corvis ST with refractive errors and ocular biometry in an unselected sample of young adults. Methods A total of 1645 healthy university students underwent corneal biomechanical parameters measurement by the Corvis ST. The refractive status of the participants was measured using an autorefractor without cycloplegia. Ocular biometric parameters were measured using the IOL Master. Results After adjusting for the effect of age, sex, biomechanical-corrected intraocular pressure and central corneal thickness, axial length was significantly associated with A1 velocity (A1v, β  = -10.47), A2 velocity (A2v, β  = 4.66), A2 deflection amplitude (A2DeflA, β  = -6.02), HC deflection amplitude (HC-DeflA, β  = 5.95), HC peak distance (HC-PD, β  = 2.57), deformation amplitude ratio max (DA Rmax, β  = -0.36), Ambrósio′s relational thickness to the horizontal profile (ARTh, β  = 0.002). For axial length / corneal radius ratio, only A1v ( β  = -2.01), A1 deflection amplitude (A1DeflA, β  = 2.30), HC-DeflA ( β  = 1.49), HC-PD ( β  = -0.21), DA Rmax ( β  = 0.07), stress–strain index (SSI, β  = -0.29), ARTh ( β  < 0.001) were significant associates. A1v ( β  = 23.18), HC-DeflA ( β  = -15.36), HC-PD ( β  = 1.27), DA Rmax ( β  = -0.66), SSI ( β  = 3.53), ARTh ( β  = -0.02) were significantly associated with spherical equivalent. Conclusion Myopic eyes were more likely to have more deformable corneas and corneas in high myopia were easier to deform and were even softer compared with those in the mild/moderate myopia.

Background To evaluate differences in Corvis ST tonometry (CST) parameters between healthy eyes and eyes with primary angle-closure glaucoma (PACG). Methods We retrospectively analyzed CST parameters of 24 healthy eyes and 24 eyes with PACG after 1:1 propensity score matching based on age, sex, axial length, intraocular pressure, and central corneal thickness. Differences in 12 CST parameters were evaluated using linear mixed-effects models, with group as a fixed effect and subject ID as a random intercept to account for inter-eye correlation. The models were adjusted for age, sex, axial length, intraocular pressure, and central corneal thickness. Multiple comparisons across parameters were controlled using the Benjamini–Hochberg false discovery rate procedure. Results Compared with healthy eyes, eyes with PACG exhibited greater A1 deformation amplitude and a shorter A2 time. Conclusions Compared with healthy eyes, eyes with PACG showed differences in selected CST parameters, specifically greater A1 deformation amplitude and shorter A2 time. These findings may indicate altered corneal dynamic response behavior in PACG.

Descemet Membrane Endothelial Keratoplasty (DMEK) is a surgical intervention for restoring endothelial function in Fuchs endothelial corneal dystrophy (FECD). However, changes in corneal biomechanical properties assessed using dynamic Scheimpflug analyzer (DSA) remain limited. This study aimed to assess alterations in corneal biomechanical parameters before and after surgery in patients with FECD using DSA. This prospective study included 24 FECD patients. Demographic data, visual acuity, central corneal thickness (CCT), endothelial cell count, intraocular pressure (IOP), stress strain index (SSI) and others DSA parameters were evaluated. Measurements were obtained preoperatively and at 1, 3, and 6 months after surgery. Repeated measures analysis of variance and pairwise correlations were used to assess differences and associations. Significant postoperative alterations were observed in multiple corneal biomechanical parameters. CCT, ARTh, A1 length, A1 DefA and SPA showed significant reductions over time. Conversely, the DefA max, maximum inverse radius, DA ratio, integrated radius and CBI significantly increased during follow-up. While, SSI remained stable at all time points. These findings demonstrate a biomechanical transformation following DMEK from 1 to 6 months postoperatively, reflecting the transition from a swollen, thickened cornea to a thinner, clearer cornea in the postoperative state. DMEK resulted in reduced corneal thickness and significant changes in several corneal biomechanical parameters. However, the stability of SSI, which is independent of CCT and bIOP, suggests that intrinsic corneal stiffness remains unchanged despite postoperative remodeling. The observed biomechanical alterations may provide useful markers for monitoring corneal recovery following DMEK.