Corneal Hysteresis Values Research Articles

Long-term results of combined surgery in patients with cataract and glaucoma

Aim. To evaluate the efficacy and safety of femtolaser-assisted phacoemulsification in combination of cataract and glaucoma in combination with NPDS in long-term follow-up.
 Materials and methods. A retrospective analysis of the results of the surgical treatment of patients with combined pathology of cataract and glaucoma was carried out. The groups of patients differed according to the method of surgical intervention: 1) phacoemulsification with NPDS and implantation of the Xenoplast drainage (49 eyes, 43 patients); 2) femtolaser-assisted phacoemulsification with NPDS and Xenoplast drainage implantation (27 eyes, 23 patients).
 Results. Before surgery, the average values ​​of corneal-compensated intraocular pressure (IOP cc), pressure equated to Goldman pressure (IOP g) and corneal hysteresis (CH) in group 1 were 27.99.9 mm Hg. Art., 27.78.9 mm Hg. Art., 7.03.0 mm Hg. Art.; in group 2 - 25.98.4 mm Hg. Art., 24.77.7 mm Hg, 7.72.1 mm Hg Art. 5 years after the surgical treatment, the average values ​​of IOP cc, IOP g and CH of the 1st group were 17.13.8 mm Hg. Art., 14.52.8 mm Hg. Art., 8.52.6 mm Hg. Art.; 2nd group - 15.13.3 mm Hg. Art., 15.34.7 mm Hg, 8.31.0 mm Hg Art. In both groups, normalization of IOP and CH was noted in the late postoperative period.
 Conclusion. Combined phacoemulsification with femtolaser accompaniment and non NPDS with Xenoplast drainage implantation is an effective and safe way to improve visual functions and normalize IOP with subsequent stabilization of the glaucoma process in the late postoperative period.

The Effect of Childhood Obesity on Intraocular Pressure, Corneal Biomechanics, Retinal Nerve Fiber Layer, and Central Macular Thickness.

Elevated corneal hysteresis (CH) and resistance factor (CRF) in obese and overweight children imply weight's effect on corneal biomechanics. Increased Goldmann-correlated intraocular pressure (IOPg) in obese children indicates glaucoma risk, emphasizing screening for IOP and retinal changes. To evaluate the effect of obesity on corneal biomechanics, retinal nerve fiber layer (RNFL), and central macular thickness (CMT) in children. In this prospective, cross-sectional, comparative study, 146 eyes of normal-weight, over-weight, and obese children aged between 6 to 17 years were evaluated. The IOPg, corneal compensated IOP (IOPcc), CH, CRF, and the average retinal nerve fiber layer (RNFL), average cup-to-disk ratio (c/d), and central macular thickness (CMT) were measured by Ocular Response Analyser and Spectral-Domain Optical Coherence Tomography (SD-OCT), respectively. There was no statistically significant difference regarding age, gender, IOPcc, average RNFL thickness, c/d ratio, and CMT among the groups ( P ≥0.05). The IOPg was significantly higher in obese children compared with normal-weight children, while CH and CRF values were significantly higher in both obese and over-weight children compared with healthy ones ( P <0.05). There was a positive correlation between BMI percentile and IOPg, CH, and CRF values. In our study, higher IOPg, corneal hysteresis, and corneal resistance factor values suggest that obese children could be potential candidates for glaucoma. Therefore, it would be appropriate to screen them for IOP and retinal alterations. Further investigations with larger sample size and longer follow-up are needed to understand the risk of glaucoma in obese children.

In vivo assessment of the ocular biomechanical properties in patients with idiopathic normal pressure hydrocephalus

PurposeIdiopathic 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.

Reliability of Measurements Using Ocular Response Analyzer as a Screening Tonometer and Corneal Hysteresis Values in the Presence or Absence of Glaucomatous Changes in Fundus.

Use of the Ocular Response Analyzer (ORA) as a screening tonometer in clinical practice yielded reliable measurements in over 80% of eyes screened. Including corneal hysteresis (CH) data in screening may improve the accuracy of glaucoma detection. To examine measurement reliability when the ORA is used as a screening tonometer, and to compare CH measurements in eyes with and those without glaucomatous changes in the fundus. 1488 eyes of 747 patients (mean age: 53.5 ± 20.4y, range: 6-94y) underwent intraocular pressure (IOP) measurement using ORA as screening. The percentage of eyes with a waveform score ≥6, the recommended threshold indicating reliability, was calculated. Eyes that had waveform score ≥6 and had undergone fundus photography and optical coherence tomography were assessed for the presence or absence of glaucomatous changes in fundus from optical coherence tomography and fundus images, and CH was compared between the 2 groups. Mean ± SD (range) of ORA measurements were: Goldmann-correlated IOP 14.9 ± 4.8 (1.0-63.2)mmHg, corneal-compensated IOP 16.2 ± 4.7 (3.2-73.6)mmHg, CH 9.7 ± 1.5 (0.0-20.6)mmHg, and waveform score 7.3 ± 1.5 (0.1-9.7). Eighty-four percent of eyes had a waveform score ≥6. Among 192 eyes (127 patients, aged 53.5 ± 18.0y) with waveform score ≥6 and evaluable for glaucomatous changes in the fundus, 53 eyes were determined as positive and 139 eyes as negative. CH was 9.6 ± 1.4 (6.8-13.3)mmHg in the positive group and 10.2 ± 1.2 (6.9-13.3)mmHg in the negative group, and was significantly lower in the positive group ( P =0.003). When using ORA as a screening tonometer, reliable results were obtained in ~80% of the eyes. CH was lower in the glaucomatous change-positive group compared with the glaucomatous change-negative group, but the ranges overlapped between the 2 groups.

Analysis of potential impact factors of corneal biomechanics in myopia

PurposeTo investigate potential impact factors associated with corneal biomechanical properties in Chinese myopia and further to investigate quantifying corneal biomechanics in clinical work.MethodsThree hundred fifty-five eyes from 181 healthy myopic subjects with a mean age of 25.1 ± 9.4 were recruited in this study. Each patient carried out a comprehensive ophthalmic examination, including corneal hysteresis(CH), corneal resistance factor(CRF), central corneal thickness(CCT), axial length(AL), intraocular pressure(IOP), spherical equivalence(SE) and corneal curvature (K). CH and CRF were measured with the ocular response analyzer(ORA). To analyze the corneal biomechanical characteristics of myopia patients and their association with other parameters.ResultThe multiple linear regression analysis showed that CH was positively associated with CCT, and corneal curvature (all with P < 0.05) and negatively associated with SE and AL)(all with P < 0.05); CRF was positively correlated with CCT, corneal curvature and IOP(all with P < 0.05), but negatively correlated with SE and AL(all with P < 0.05). The CH and CRF values in children group were both higher than adults group (≥ 18 years old) (P < 0.05), but it attributed to that the CCT of children was thicker than adults. Excluding factor of CCT, there was no significant difference in CH and CRF between children group and adult group. Excluding factor of CCT, there was no significant difference in CH and CRF among different stage of age (age 18–48).ConclusionThe CCT played the most important role of affecting the CH and CRF. The SE, corneal curvature, AL and IOP had a certain influence on corneal biomechanics. Whether the CH and CRF values of individual patient are normal in clinical work, it should refer to the CH and CRF values corresponding CCT sectional range and SE.

Correlation between Interocular Asymmetry of Corneal Hysteresis and Visual Field Defect in Glaucoma.

To evaluate the relationship between interocular asymmetries of corneal hysteresis (CH) and visual field defects in Korean patients with glaucoma. A total of 444 eyes from 222 participants with glaucoma in at least one eye were enrolled. CH was measured using an ocular response analyzer (Reichert Technologies Inc). Eyes of each participant were classified into "better eye" and "worse eye" based on the mean deviation (MD) value of visual field test. The correlation between interocular differences in intraocular pressure, axial length, central corneal thickness, CH, and MD values was evaluated using Spearman correlation analysis. To exclude the possible effect of antiglaucoma medication on corneal properties, additional analyses were performed on eyes without any glaucoma treatment at the time of CH measurement (treatment-naive group). Median (interquartile range) MD value was -3.71 dB (-6.87 to -1.30 dB) in the better eye and -10.20 dB (-16.32 to -5.62 dB) in the worse eye. When the correlation between the asymmetry of the MD value and asymmetry of intraocular pressure, axial length, central corneal thickness, and CH were evaluated, only interocular differences in CH were significantly associated with interocular differences in MD values (rho = 0.214, p = 0.001). Among the 222 participants, 60 (27.0%) were treatment-naive group. In these eyes, interocular differences in CH were also significantly associated with interocular differences in the MD values (rho = 0.285, p = 0.029). The interocular asymmetry of CH was significantly correlated with the interocular asymmetry of visual field defects in glaucoma.

Corneal Hysteresis in Adult Indian Population

Purpose: To evaluate corneal hysteresis (CH) and to study its inter-ocular variability along with its association with gender and age using Ocular Response Analyzer (ORA) among healthy adult Indian population. Methods: This prospective, cross-sectional, observational study was conducted at a tertiary eye care centre in a medical university in India between July and December 2020. 300 healthy participants in age group between 18 to 60 years were recruited from amongst the residents, staff and patients coming for routine examination in Ophthalmology department. Participants with history of systemic/ocular disease, ocular surgery, pregnancy or spherical equivalent refraction &gt;±1D were excluded from study. CH and corneal compensated intra-ocular pressure (IOP-cc) was assessed using ORA. Statistical analysis was done to calculate mean CH in study population. Inter-ocular and gender-wise variability in mean CH was analysed using independent-t test. Pearson correlation coefficient was calculated to study correlation of CH between eyes and with age, gender, IOP-cc and central corneal thickness (CCT). Results: 162 males and 134 females were recruited. The mean age was 37.5±11 years and mean CH in overall study population, males and females were 10.57±1.12, 10.25±0.90, 10.96±1.22 mm Hg. No significant difference in CH, IOP-cc and CCT was observed between eyes. A strong positive correlation was observed in CH between eyes (r=0.75, p&lt;0.001). Conclusions: Mean CH among healthy Indian adult is 10.57±1.12 mm Hg. CH values are higher among females compared to males. CH values between the two eyes in normal individuals are coherent and positively correlated.

Evaluation of the corneal biomechanical properties and corneal thickness in patients with Graves' orbitopathy.

To evaluate the corneal biomechanical properties and central corneal thickness in patients with Graves' orbitopathy (GO). 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. The mean CH values were found as 9.6 ± 1mmHg in Group 1, 10.2 ± 0.9mmHg in Group 2, and 11.4 ± 1.7mmHg 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 ± 3.6mmHg in Group 1, 15.8 ± 4.0mmHg in Group 2 and 15.2 ± 4.1mmHg in the Control Group. The IOPcc and IOPg measurements between all groups were statistically significant (p = 0.009, p = 0.027, respectively). Corneal biomechanical measurements were different in the GO patients with varying CAS scores compared to healthy individuals.

Effect of Corneal Hysteresis on the Rates of Microvasculature Loss in Glaucoma

To investigate the association between corneal hysteresis (CH) and rates of optic nerve head whole image capillary density (wiCD) loss over time in open-angle glaucoma (OAG). Observational cohort. One hundred seventy-four eyes (122 OAG and 52 glaucoma suspect eyes) from 112 patients over more than 2 years and 4 visits or more. Baseline CH measurements were acquired with the Ocular Response Analyzer. Linear mixed-effect models were designed to investigate the effect of CH, average intraocular pressure (IOP) during follow-up, and baseline visual field (VF) mean deviation (MD) on the rates of wiCD loss and circumpapillary retinal nerve fiber layer (cpRNFL) thinning over time, while adjusting for confounders. Interaction between CH or baseline MD and average IOP during follow-up were included in final models to evaluate the effect of baseline MD or average IOP during follow-up on structural changes for different values of CH. Effect of CH, IOP, and baseline MD on the rates of wiCD loss and cpRNFL thinning over time. The average follow-up time was 3.9 years. In the multivariable model, non-Black race, higher average IOP during follow-up, lower baseline CH, lower baseline VF MD, and higher numbers of IOP-lowering medications were associated with faster rates of wiCD loss over time. For CH values 6 mmHg and 12 mmHg, every 1-mmHg increase in average IOP during follow-up was associated with 0.23% per year faster and 0.07% per year slower rates of wiCD loss over time, respectively. While every 1-mmHg decrease in CH was associated with 1.89% per year faster rate of wiCD loss for MD of -12 dB, it was associated with 0.81% per year faster rate of wiCD loss for MD of -3 dB. Lower CH values were significantly associated with faster rates of wiCD loss over time. In eyes with lower CH, both higher average IOP during follow-up and more severe glaucoma damage at baseline were associated with faster rates of wiCD loss and cpRNFL thinning. These results support CH as a useful parameter for risk assessment of glaucoma progression. Proprietary or commercial disclosure may be found after the references.

Diurnal Variation of Corneal Hysteresis in Patients With Untreated Primary Open Angle Glaucoma and Normal Individuals.

Corneal hysteresis in both patients with untreated open angle glaucoma and normal individuals demonstrated significant diurnal variation independent of confounding factors and was higher in the nighttime than in the daytime. To investigate diurnal variations in corneal hysteresis (CH) in patients with untreated primary open angle glaucoma (POAG) and normal individuals by using an ocular response analyzer. This prospective study included 72 eyes of 53 patients with untreated POAG and 53 eyes of 47 normal individuals. Intraocular pressure (IOP) and CH were measured using Goldmann applanation tonometry (GAT) and ocular response analyzer, respectively, every 3 hours from 9:00 to 24:00. Mixed-effects models were used to determine factors associated with CH values and CH amplitude (maximum values minus minimum values) and to examine the diurnal variations in GAT IOP and CH in each group. Significant differences between time points were defined as significant variations. The diurnal average GAT IOP and CH in patients with POAG were significantly higher and lower than those in normal individuals ( P =0.001, 0.002). In the multivariate analysis, the larger central corneal thickness was associated with larger CH values in POAG and normal eyes (both P <0.001). A larger amplitude of GAT IOP was significantly associated with a larger CH amplitude in POAG and normal eyes ( P =0.010, 0.013). CH, in both groups, showed similar significant diurnal variation and was higher in the nighttime than in the daytime, even after adjusting for confounding factors, while IOP showed an antiphase pattern. CH in both untreated POAG patients and normal participants demonstrated similar diurnal variations, that is, higher at night, independent of confounding factors. These findings suggest that viscoelastic properties of the cornea may fluctuate diurnally independent of IOP.

Corneal Biomechanical Parameters after 60-Year-Old.

To determine the distribution of corneal biomechanical parameters in an elderly population. This cross-sectional study was conducted in subjects above 60 years living in Tehran. The participants were selected using multi-stage cluster sampling. Corneal biomechanical parameters were measured in a randomly selected subsample of this population using the Reichert Ocular Response Analyzer (Reichert Ophthalmic Instruments, Inc., Buffalo, NY, USA). Of 470 subjects, the data of 420 participants aged over 60 years were analyzed (mean age: 69.3 ± 6.5 years and range: 61-88 years), 363 (86.4%) of whom were male. The mean and standard deviation of corneal hysteresis (CH) and corneal resistance factor (CRF) were 8.37 ± 1.55 mmHg (95% confidence interval [CI]: 8.02-8.72) and 9.06 ± 1.70 mmHg (95% CI: 8.69-9.44), respectively. The mean CH was 8.27 ± 1.54 mmHg in men and 9.25 ± 1.28 mmHg in women, and the mean CRF was 9.00 ± 1.71 mmHg in men and 9.63 ± 1.37 mmHg in women. According to the results of multiple linear logistic regression analysis, CH had a significant association with younger age (β = -0.05, P = 0.032), female sex (β = 1.83, P < 0.001), reduced maximum keratometry (β = -0.22, P = 0.06), and increased anterior chamber volume (β = 0.01, P = 0.007). CRF had a significant correlation with a younger age (β = -0.06, P = 0.02), female sex (β = 1.01, P = 0.05), central corneal thickness (β = 0.02, P < 0.001), and reduced maximum keratometry (β = -0.39, P = 0.010). The mean CH and CRF values were low in this sample of the Iranian population aged over 60 years indicating the weaker elasticity of the corneal connective tissue.

Corneal Hysteresis, Intraocular Pressure, and Progression of Glaucoma: Time for a "Hyst-Oric" Change in Clinical Practice?

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

The Effect of Thyroid Eye Disease on Corneal Biomechanical Properties.

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±1.91mmHg, 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;10.68 (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.

Use of corneal hysteresis and corneal resistance factor in target intraocular pressure estimation in patients with early primary open-angle glaucoma.

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). 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 12months of receiving medications; either monotherapy or combination therapy. 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. 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.

Effect of upper eyelid blepharoplasty on corneal biomechanical, topographic and tomographic parameters 4\xa0weeks after surgery

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

Synergic effect of corneal hysteresis and central corneal thickness in the risk of early-stage primary open-angle glaucoma progression.

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

Pediatric Keratoconus: Topographic, Biomechanical and Aberrometric Characteristics

This study sought to evaluate the demographic profile, clinical features, topographic features, and biomechanical and aberrometric characteristics in pediatric keratoconus (KC). Cross-sectional study. Pediatric KC cases <18 years of age were evaluated at a tertiary hospital. Main outcome measurements were demographic profile, clinical features, visual acuity, corneal topography, aberrometry, and biomechanical and confocal microscopy findings. A total of 116 eyes of 62 consecutive patients were recruited with a mean ± age of 14.7 ± 2.77 years (range: 8-18 years); 46 of 62 (88%) were males; 57 of 62 cases (92%) had bilateral disease; 53 of 116 eyes (46%) had progressive KC; and 9 of 116 eyes (8%) had acute hydrops. Systemic associations were found in 6 of 62 patients (9.7%) and ocular associations in 77 of 116 eyes (66.3%); 68 of 116 eyes (58.6%) had associated vernal keratoconjunctivitis (VKC). Among eyes with VKC, 29 of 68 eyes (46%) were in stage IV KC, versus 25% of eyes with no VKC (P= .004). The mean ± SD refractive spherical equivalent was-4.72 ± 3.32 diopters (D), and refractive astigmatism was 3.69 ± 3.09 D. The mean values of maximum keratometry, thinnest pachymetry, and corneal higher-order aberrations were 60.89 ± 10.9 D, 396.05 ± 95.03μm, and 1.18 ± 1.2μm, respectively. Values of corneal hysteresis and corneal resistance factor correlated with the stage of KC (r=-0.26; P= .007). Pediatric KC was commonly associated with VKC in this cohort. Eyes with VKC had more severe KC than those without VKC. Nearly half of the patients presented with progressive disease. Corneal biomechanical changes correlated well with stage of KC in this pediatric age group.

The Relationship Between Corneal Hysteresis and Retinal Ganglion Cells - A Step Forward in Early Glaucoma Diagnosis.

BackgroundGlaucoma is a major cause of irreversible visual field (VF) loss across the world. Many studies have assessed the accuracy of glaucoma diagnostic tests for a more precise diagnosis to quickly identify patients with higher risk of progression.Material/MethodsWe conducted a study that included 214 eyes divided into 3 groups: 79 eyes from patients diagnosed with primary open-angle glaucoma (POAG), 68 eyes from patients diagnosed with ocular hypertension (OH), and 67 eyes from normal individuals (normal eyes, NE). All patients included in the study received a complete checkup.ResultsIn POAG patients, means of central corneal thickness (CCT), corneal hysteresis (CH), corneal resistance factor (CRF), mean defect (MD), visual field index (VFI), peripapillary retinal nerve fiber layer (pRNFL), and ganglion cell complex (GCC) are lower than in OH patients, and in NE are higher than in both groups. Also, we found a statistically significant direct correlation between CH and GCC thickness. Further statistical analysis revealed that both pRNFL thickness and GCC thickness are significantly influenced by CH value in a precise manner.ConclusionsThe first cell type affected in glaucoma is the retinal ganglion cell. We found a positive correlation between GCC thickness and CH, suggesting that CH might be a parameter to consider in the evaluation of all glaucoma patients from their first examination. Moreover, both pRNFL thickness and GCC thickness are influenced by CH, suggesting the utility of monitoring the value of CH at every checkup to detect its decrease in glaucoma patients.

Corneal Biomechanical Response Alteration After Scleral Buckling Surgery for Rhegmatogenous Retinal Detachment

To compare the corneal biomechanics of eyes that underwent scleral buckle (SB) for rhegmatogenous retinal detachment (RRD) with those of fellow eyes (fellow eyes) and to further investigate the effects of SB on intraocular pressure (IOP) values. Retrospective, fellow-eye matched cohort study. A total of 18 consecutive patients (11 males and 7 females) treated with SB for RRD in 1 eye were enrolled. Goldmann applanation tonometry was used to measure IOP. Biomechanical properties of the cornea were investigated by using the Ocular Response Analyzer (ORA) (Reichert Instruments) for the calculation of corneal resistant factor (CRF), corneal hysteresis, Goldmann-correlated IOP, and corneal-compensated IOP. Customized software was used for analysis of the ORA infrared and pressure signals, and a significance threshold was set to a P value of .05. Operated eyes (OEs) showed significantly lower values of corneal hysteresis and CRF than fellow eyes (9.0 ± 1.8 vs 10.1 ± 1.8mm Hg, respectively; P < .001; 10.0 ± 2.2 vs 10.9 ± 2.2mm Hg; P < .001). GAT was significantly lower than corneal-compensated IOP in OEs (18.1 ± 4.9 vs 19.8 ± 4.8mm Hg, respectively; P= .022) but not in fellow eyes. The second applanation event (A2) took place earlier in time, and the cornea was moving faster during A2 in the OEs than in the fellow eyes. SB for the treatment of RRD affects corneal biomechanical response, likely due to a less compliant sclera that limits corneal motion and reduces energy dissipation, reflected in a lower corneal hysteresis. This has potentially meaningful clinical implications as the accuracy of the measurement of IOP values may be affected in these eyes.

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

To determine the changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with controls. Pertinent studies were identified by comprehensively search of PubMed, Embase, the Web of Science, the Cochrane Library, Scopus, the China National Knowledge Infrastructure and the Chinese biomedical disc (CBM) databases. Pooling analyses by random models using the D-L method were performed for corneal hysteresis (CH), the corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOPg). A total of 15 studies were included in the final analysis, involving 1506 eyes in the diabetic group and 2190 eyes in the control group. The diabetic group had significantly higher CH, CRF, IOPg and IOPcc values than the control group. The pooled mean differences were 1.34mmHg (95% confidence interval [CI] 0.60-2.08mmHg, P < 0.001) for IOPg and 0.85mmHg (95% CI 0.18-1.51mmHg, P = 0.013) for IOPcc, 0.38mmHg (95% CI 0.01-0.75, P = 0.047) for CH and 0.63mmHg (95% CI 0.27-0.98, P = 0.001) for the CRF. Sensitivity analyses using the leave-one-out method showed a consistent significant difference between the groups (all P < 0.001). Corneal biomechanics changed in the patients with DM. High CH, CRF, IOPcc and IOPg values may be associated factors for diabetes mellitus. Future studies are warranted to clarify the underlying mechanisms and explore the relationship between corneal biomechanics, glaucoma and diabetes mellitus. PROSPERO registration No CRD4201705465.