Relationship between corneal biomechanical properties and structural biomarkers in patients with normal-tension glaucoma: a retrospective study

Changes in corneal biomechanics in patients with glaucoma: a systematic review and meta-analysis

INTRODUCTION

Corneal biomechanics has been implicated in a variety of ocular diseases. The purpose of this study was to evaluate the relationship between the glaucoma and corneal biomechanical properties, and exploring the value of corneal biomechanics in the diagnosis and follow-up of glaucoma diseases.

METHODS

We searched studies in PubMed, EMBASE, Web of Science and clinicaltrials.gov., as of October 8, 2022. Only English studies were included, without publication time limit. We also searched the reference lists of published reviews. This meta-analysis was conducted with random-effects models, we used mean difference(MD) to evaluate the outcome, and the heterogeneity was assessed with the I2 statistic. Subgroup analyses were performed under the appearance of high heterogeneity. We used 11 items to describe the characteristics of included studies, publication bias was performed through the Egger's test. The quality assessment were evaluated by Newcastle-Ottawa Scale(NOS) items.

RESULTS

A total of 27 eligible studies were identified for data synthesis and assessment. The result of meta-analysis showed that in the comparison of included indicators, the corneal biomechanics values of glaucoma patients were statistically lower than those of normal subjects in a similar age range. The covered indicators included central corneal thickness(CCT) (MD = -8.34, 95% CI: [-11.74, -4.94]; P < 0.001), corneal hysteresis(CH)(MD = -1.54, 95% CI: [-1.88, -1.20]; P < 0.001), corneal resistance factor(CRF)( MD = -0.82, 95% CI: [-1.21, -0.44]; P < 0.001), and intraocular pressure(IOP)( corneal-compensated intraocular pressure (IOPcc): MD = 2.45, 95% CI: [1.51, 3.38]; P < 0.001); Goldmann-correlated intraocular pressure (IOPg): MD = 1.30, 95% CI: [0.41, 2.20]; P = 0.004), they all showed statistical difference. While the value of axial length(AL) did not show statistically different(MD = 0.13, 95% CI: [-0.24, 0.50]; P = 0.48).

CONCLUSION

Corneal biomechanics are associated with glaucoma. The findings can be useful for the design of glaucoma screening, treatment and prognosis.

The influence of topical anesthetic and fluorescein on non-contact tonometry measurements using ultra-high-speed dynamic Scheimpflug

This study aimed to investigate the effects of topical anesthetic and fluorescein drops on intraocular pressure (IOP), central corneal thickness (CCT) and biomechanical properties as measured by Corvis ST (CST-Oculus; Wezlar, Germany) in healthy eyes. A cross-sectional observational study was conducted on 46 healthy patients. The CST measurements were obtained before and immediately after the instillation of topical anesthetic and fluorescein drops. Pre-post instillation data were statistically analyzed. IOP measurements were compared to Goldmann's Applanation Tonometry (GAT), which was also performed after drops instillation. Biomechanical parameters analyzed included applanation 1 velocity, applanation 2 velocity, applanation 1 time, applanation 2 time, whole eye movement, deflection amplitude, and stiffness parameter at first applanation. A statistically significant difference in IOP, both for non-corrected IOP (IOPnct) and biomechanically corrected IOP (bIOP), was observed before and after the instillation of eyedrops. Despite this statistical significance, the observed difference lacked clinical relevance. The IOPnct demonstrated a significant difference pre and post-anesthetic and fluorescein instillation compared to GAT (14.99 ± 2.27 mmHg pre-instillation and 14.62 ± 2.50 mmHg post-instillation, versus 13.98 ± 2.04 mmHg, with p-values of 0.0014 and 0.0490, respectively). Comparable findings were noted when justaposing bIOP to GAT (14.53 ± 2.10 mmHg pre-instillation and 13.15 ± 2.25 mmHg post-instillation, against 13.98 ± 2.04 mmHg, with p-values of 0.0391 and 0.0022, respectively). Additionally, CCT measurements revealed a statistically significant elevation following the administration of topical anesthetic and fluorescein drops (from 544.64 ± 39.85 µm to 586.74 ± 41.71 µm, p < 0.01. None of the analyzed biomechanical parameters showed statistically significant differences after drops instillation. While the administration of topical anesthetic and fluorescein drops induced a statistically significant alteration in both IOPnct and bIOP readings, these changes were not clinically consequential. Furthermore, a notable statistical rise was observed in CCT measurements post-drops instillation, as determined by CST. Yet, corneal biomechanical parameters remained unaffected.

Corneal Biomechanical Measures for Glaucoma: A Clinical Approach

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.

Corneal Biomechanical Properties of Various Types of Glaucoma and Their Impact on Measurement of Intraocular Pressure

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.

Corneal Biomechanics in Primary Open Angle Glaucoma and Ocular Hypertension: A Systematic Review and Meta-analysis

PRCIS

Normal tension glaucoma patients had softer corneas than normal controls, whereas high-tension glaucoma and ocular hypertension patients had stiffer corneas.

PURPOSE

To comprehensively identify the corneal biomechanical differences of patients with primary open angle glaucoma (POAG) and ocular hypertension (OHT) using the Ocular Response Analyzer or the Corvis ST.

METHODS

The electronic databases PubMed, Embase, and Web of Science were comprehensively searched for studies comparing corneal biomechanical differences between POAG and OHT patients with normal controls by Ocular Response Analyzer or Corvis ST. The weighted mean differences and 95% confidence intervals (CIs) were calculated. Subgroup analyses were performed according to the subtypes of POAG, including high-tension glaucoma (HTG) and normal tension glaucoma (NTG).

RESULTS

Thirty-one case-control studies were ultimately included, with 2462 POAG patients, 345 OHT patients, and 3281 normal controls. The corneal hysteresis (CH), corneal resistance factor (CRF), and highest concavity time (HC-t) were all lower in POAG patients than in normal controls. The CH, time at the second applanation (A2t), HC-t, highest concavity radius (HC-R), and deformation amplitude at the highest concavity (HC-DA) were lower in OHT patients, while the CRF, time at the first applanation (A1t), and stiffness parameter at the first applanation (SP-A1) were greater in OHT patients than in normal controls. The subgroup analyses showed that the CH, A2t, length at the second applanation (A2L), and HC-DA were lower in HTG, and the CH, CRF, A1t, and HC-t were lower in NTG patients than in normal controls.

CONCLUSION

The corneas of NTG patients are more deformable than normal controls, whereas the corneas of HTG and OHT patients are stiffer.

Comparison of two analyzer measurements focusing on material stiffness among normal, treatment-naïve, and treated glaucoma eyes

To investigate differences in biomechanical properties focusing on stiffness parameters between normal, treatment-naïve primary open-angle glaucoma (POAG), and treated POAG eyes. Retrospective case-control study, This study included 46 treatment-naïve POAG eyes, 46 POAG eyes treated with prostaglandin analogues, and 49 normal eyes used as controls; matched in terms of age and axial length. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using an ocular response analyzer (ORA). Fifteen biomechanical parameters were measured with the Corneal Visualization Scheimpflug Technology (Corvis ST), including biomechanical glaucoma factor (BGF) and two stiffness parameters of 'SP A1' and 'stress-strain index (SSI)', which were compared among the three groups. Additionally, the area under the curve (AUC) values of the receiver-operating curve to discriminate control and treatment-naïve POAG eyes were calculated for BGF and CH. Treatment-naïve POAG eyes had higher 'SSI' than normal eyes even after controlling for IOP (p < 0.05, Tukey-Cramer test). Treated POAG eyes had significantly lower CRF, and higher BGF than treatment-naïve POAG eyes. There were also significant differences in CH or SP A1 among the three groups. BGF and CH had similar AUC values (0.61 and 0.59). Treatment-naïve POAG eyes had stiffer corneas compared to normal eyes, which seemed to result from the material/structure of the cornea rather than higher intraocular pressure. Antiglaucoma topical medication alters biomechanical properties measured with Corvis ST. These results are important for understanding the pathogenesis and improving the management of POAG.

The Comparison of Age-related Change in Retinal Nerve Fiber Layer and Ganglion Cell Complex Thicknesses between Glaucoma Suspects and Healthy Individuals

Aim

The purpose of this study is to investigate the difference of change in the retinal nerve fiber layer (RNFL) and the ganglion cell complex (GCC) thickness according to age in glaucoma suspect individuals and healthy subjects.

Materials and methods

Thicknesses of RNFL and GCC were measured with spectral domain optical coherence tomography (SD-OCT) in glaucoma-suspected individuals and healthy subjects. The differences in age, overall mean, four quadrants, and 12 clock-hour sectors of RNFL and overall mean, superior half, and inferior half GCC thicknesses between glaucoma suspects and healthy participants were analyzed and compared using linear regression analyses.

Results

There were 201 glaucoma-suspect individuals and 121 healthy subjects with a mean age of 38.89 and 40.26 years, respectively (p = 0.27). The mean overall RNFL thickness was found to be 97.76 and 97.43 µm in healthy individuals and glaucoma suspects (p = 0.72). The mean overall GCC thickness was found to be 111.30 and 104.67 µm in healthy individuals and glaucoma suspects, respectively (p < 0.001). There was a 0.11 µm decrease per year found in overall GCC thickness in glaucoma suspects and 0.23 µm decreases per year in overall GCC thickness in healthy individuals (p < 0.001). There was a 0.02 µm decrease per year found in overall RNFL thickness in glaucoma suspects and a 0.29 µm decrease per year in overall RNFL thickness in healthy individuals (p < 0.001). However, these per-year decreases in GCC thickness glaucoma suspects and healthy individuals were not found to be statistically significant (p = 0.21); on the other hand, this difference for RNFL thickness was significant (p < 0.001).

Conclusion

It was found that the thicknesses of RNFL and GCC were different between glaucoma suspects and healthy individuals. However, age-related decay in the RNFL and GCC thicknesses was not uniform in healthy individuals and glaucoma suspects.

Clinical significance

It was found that the RNFL thickness and GCC thickness were lower in glaucoma suspects than in healthy controls eyes. However, an age-related decrease of RNFL and GCC thicknesses were found to be less in glaucoma suspects compared with healthy controls.

How to cite this article

Firatli G, Elibol A, Altinbas E, et al. The Comparison of Age-related Change in Retinal Nerve Fiber Layer and Ganglion Cell Complex Thicknesses between Glaucoma Suspects and Healthy Individuals. J Curr Glaucoma Pract 2023;17(1):22-29.

Evaluation of corneal biomechanical properties using the ocular response analyzer and the dynamic Scheimpflug-Analyzer Corvis ST in high pressure and normal pressure open-angle glaucoma patients

PURPOSE

To characterize differences in corneal biomechanics in high (HPG) and normal pressure (NPG) primary open-angle glaucoma, and its association to disease severity.

METHODS

Corneal biomechanical properties were measured using the Ocular Response Analyzer (ORA) and the dynamic Scheimpflug-Analyzer Corvis ST (CST). Disease severity was functionally assessed by automated perimetry (Humphrey field analyzer) and structurally with the Heidelberg Retina Tomograph. To avoid a possible falsification by intraocular pressure, central corneal thickness and age, which strongly influence ORA and CST measurements, group matching was performed. Linear mixed models and generalized estimating equations were used to consider inter-eye correlation.

RESULTS

Following group matching, 60 eyes of 38 HPG and 103 eyes of 60 NPG patients were included. ORA measurement revealed a higher CRF in HPG than in NPG (P < 0.001). Additionally, the CST parameter integrated radius (P < 0.001) was significantly different between HPG and NPG. The parameter SSI (P < 0.001) representing corneal stiffness was higher in HPG than in NPG. Furthermore, regression analysis revealed associations between biomechanical parameters and indicators of disease severity. In HPG, SSI correlated to RNFL thickness. In NPG, dependencies between biomechanical readings and rim area, MD, and PSD were shown.

CONCLUSION

Significant differences in corneal biomechanical properties were detectable between HPG and NPG patients which might indicate different pathophysiological mechanisms underlying in both entities. Moreover, biomechanical parameters correlated to functional and structural indices of diseases severity. A reduced corneal deformation measured by dynamic methods was associated to advanced glaucomatous damage.

Corneal Biomechanics - an Emerging Ocular Property with a Significant Impact

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

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.

Discrepancy between NTG and POAG with corneal nerves in CCM

BACKGROUND

To investigate the morphological features of corneal subbasal nerve plexus (CSNP) in normal-tension glaucoma (NTG) and primary open-angle glaucoma (POAG).

METHODS

Thirty-four eyes with NTG (16 untreated), 23 eyes with POAG (11 untreated) and 31 eyes of healthy subjects were recruited. CSNP were assessed by corneal confocal microscopy (CCM) and peripapillary retinal nerve fibre layer (RNFL) was measured with optical coherence tomography (OCT). CCM parameters including corneal subbasal nerve fibre length (FL), corneal subbasal nerve branch number (BN), corneal subbasal nerve width (NW), corneal subbasal nerve reflectivity (NR), total and local corneal subbasal nerve tortuosity (NT) was compared across all groups, as well as between the topical medication treated and the nontreated patients.

RESULTS

The newly diagnosed NTG patients had the longest FL (3619.15 ± 501.55), most BN (21.02 ± 5.90), thinnest corneal subbasal nerve width (3.04 ± 0.82), corneal subbasal nerve lowest reflectivity (140.43 ± 10.24) and the corneal subbasal nerves were most bending (1.09 ± 0.06) and tortuous (123.36 ± 7.82) compared with untreated POAG patients and controls. Untreated POAG had similar CSNP to controls. The treated glaucoma patients had longer FL and more BN than the nontreated but with no significant difference. FL and BN had correlations with RNFL thickness in untreated NTG patients, and NR and NW had correlations with RNFL thickness in untreated POAG patients. NT had no correlations with RNFL thickness.

CONCLUSIONS

The NTG group had different CSNP characteristics from the POAG group and controls, while the latter two shared more morphological features. The CCM parameters except NT had associations with the RNFL thickness in glaucoma patients.

The Association Between Ocular Rigidity and Neuroretinal Damage in Glaucoma

Purpose

Ocular rigidity (OR) is an important biomechanical property, thought to be relevant in the pathophysiology of open-angle glaucoma (OAG). This study aims to evaluate the relationship between OR and neuroretinal damage caused by glaucoma.

Methods

One hundred eight subjects (22 with healthy eyes, 23 with suspect discs, and 63 with OAG) were included in this study. OR was measured using a noninvasive optical coherence tomography (OCT)-based method developed by our group. We also measured central corneal thickness (CCT), corneal hysteresis (CH), and corneal resistance factor (CRF). Pearson and partial correlations were performed to evaluate the relationship between OR and glaucomatous damage represented by ganglion cell complex (GCC), retinal nerve fiber layer (RNFL) thicknesses, and neuroretinal rim area.

Results

Significant positive correlations were found between OR and minimum GCC thickness (r = 0.325, P = 0.001), average GCC thickness (r = 0.320, P = 0.002), rim area (r = 0.344, P < 0.001), and RNFL thickness in the superior (r = 0.225, P = 0.023), and inferior (r = 0.281, P = 0.004) quadrants. These correlations were generally greater than those found for CCT, CH, and CRF. Furthermore, no correlation was found between OR and corneal biomechanical parameters. After adjusting for age, sex, and ethnicity, significant correlations were found between OR and minimum and average GCC thickness (r = 0.357, P = 0.001 and r = 0.344, P = 0.001, respectively), rim area (r = 0.327, P = 0.001), average RNFL thickness (r = 0.331, P = 0.001), and RNFL thickness in the superior (r = 0.296, P = 0.003) and inferior (r = 0.317, P = 0.001) quadrants.

Conclusions

In this study, we found a positive correlation between structural OCT-based parameters and OR, indicating more neuroretinal damage in eyes with lower OR. These findings could provide insight into the pathophysiology of OAG.

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

BACKGROUND Glaucoma 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 AND METHODS We 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. RESULTS In 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. CONCLUSIONS The 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.

Is the Corneal Thickness Profile Altered in Diabetes Mellitus?

Purpose: To investigate the influence of chronic hyperglycemia in diabetes mellitus (DM) on spatial corneal thickness distribution and to analyze the influence of disease-specific factors. Methods: DM patients and healthy subjects were matched according to age and intraocular pressure (IOP). In diabetics, disease duration, DM type, and HbA_1c value were assessed. Spatially resolved corneal thickness was measured by Pentacam HR. Thinnest corneal thickness (TCT) and peripheral pachymetry of concentric circles around TCT were determined. The Dynamic Scheimpflug Analyzer Corvis ST (CST) was used to measure the parameter pachy slope, which is an indicator of the change of corneal thickness from the apex to the periphery. Results: 59 DM patients and 57 healthy subjects were included. Age (P = .486) and IOP (P = .154) were not different between the groups. In DM, pachy slope was significantly higher than in healthy subjects (41.1 ± 9.87 vs. 35.18 ± 10.64 μm, P = .004). Also, the differences between TCT and the average of peripheral corneal thickness of concentric circles with a diameter of 2 mm (10.3 ± 1.7 vs. 9.3 ± 3.8 μm, P < .001) to 6 mm (82.2 ± 12.4 vs. 76.8 ± 12.6 μm, P = .011) were increased in patients. Changes in thickness profile were associated with HbA_1c value and presence of diabetic retinopathy or maculopathy. Conclusion: In DM, a stronger peripheral corneal thickness increase was detectable. This change was shown using the novel CST parameter pachy slope and confirmed by Pentacam readings. These alterations might affect IOP and biomechanical measurements, and influence refractive procedures.

The association between oxidative stress and corneal hysteresis in patients with glaucoma

Systemic antioxidative status has been implicated in glaucoma pathogenesis. Additionally, corneal hysteresis (CH) may contribute to glaucoma progression. Here, we evaluated the relationship between biological antioxidant potential (BAP) and CH. This study included 103 patients with open-angle glaucoma (OAG). We used a free radical analyzer to measure BAP, and an ocular response analyzer to measure CH and corneal resistance factor (CRF). We evaluated the relationship between systemic oxidative stress and other clinical parameters with Spearman's rank correlation test and a multi-regression analysis. BAP was not correlated to either CH or CRF in the male or female OAG patients. BAP was correlated to both CH and CRF in the female OAG patients older than 57 years (r = 0.51, P = 0.003; r = 0.49, P = 0.004), but uncorrelated in the female OAG patients younger than 57 years. Multiple regression analysis revealed that BAP independently contributed to CH (P = 0.025) and CRF (P = 0.015) in the older female OAG patients. Systemic oxidative stress may significantly affect the viscoelasticity of the cornea in older female OAG patients. Future studies are needed to confirm that low systemic antioxidative status and low corneal hysteresis contribute to glaucoma pathogenesis.

Correlations between corneal biomechanics and specular microscopy in patient with cataract

This study aimed to analyze the connection between corneal biomechanics (corneal hysteresis, CH) and endothelial cell density of cornea (mean endothelial cell density, MCD) in patients diagnosed with cataract. This retrospective, observational study was performed in the Ophthalmology Clinic of the University Emergency Hospital in Bucharest. Of 60 patients (120 eyes) with cataract, who were included in this study, we analyzed the CH values obtained using with the Ocular Response Analyzer (ORA) and the MCD values obtained using the specular microscopy. The study groups comprised both men and women with ages ranging from 45 to 63 years. Patients were divided into three study groups according to CH values. In each batch, the CH values obtained with the Ocular Response Analyzer (ORA) were correlated with age, gender and MCD, then the subgroups were compared. All the data gathered showed no correlation to be statistically significant regarding the biomechanical properties of the cornea and the corneal endothelial cell density in patients with cataract.

Ocular Surface Changes in Prostaglandin Analogue-Treated Patients

Glaucoma is the second leading cause of blindness globally. Reducing intraocular pressure (IOP) has been acknowledged to be the main therapy for glaucoma. Prostaglandin analogues (PGAs) have become the first-line therapy for patients with glaucoma due to their powerful efficacy for lowering (IOP). However, usage of PGAs can also cause several notable side effects, including the changes in ocular surface. The relationship between PGAs and ocular surface changes is complicated and still remains unclear. In the present review, we summarize the recent studies of the effects of PGAs on ocular changes as well as the possible mechanisms that might provide new considerations during clinical medication.

Corneal hysteresis and glaucoma

PURPOSE

To review and summarize the characteristics of corneal hysteresis (CH) and its relationship with glaucoma.

METHODS

A PubMed search was carried out using the terms "corneal hysteresis", "glaucoma", and "biomechanics". Up to March 2018, all studies published in English are included in this review.

RESULTS

The value of CH reflects the ability of corneal tissue to absorb and release energy during bidirectional flattening. It is an important biomechanical parameter of the cornea. The CH value of healthy adults is about 11 mmHg. The measurement of CH is reproducible and different. People have different CH values, which are determined by the shape of the individual's cornea. The study found that all types of glaucoma, including primary open angle glaucoma, angle-closure glaucoma, normal tension glaucoma, congenital glaucoma, binocular asymmetrical glaucoma, CH values are lower than normal people, therefore, CH is therefore a good indicator of glaucoma diagnosis and screening. Lower CH values are associated with thinner retinal nerve fiber layer (RNFL), larger linear cup/disk ratio (LCDR) and degree of optic disc defect. A lower CH value can also result in a lower visual field index. CH and the basic intraocular pressure play a synergistic role in the progression of glaucoma. The study found that CH can change with changes in basic intraocular pressure, means CH increases when intraocular pressure decreases, while the CH decreases conversely when intraocular pressure increases. Most clinical case studies have shown a decrease in CH after LASER refractive surgery. CH has its limitations, such as corneal damage or corneal surgery, but in general, CH is a risk factor for glaucoma progression.

CONCLUSION

CH is used as a predictor of glaucoma risk and may help to assess the effect of corneal thickness on intraocular pressure. The clinical significance of CH in the diagnosis and efficacy of glaucoma will become more explicit. In the future, CH can also play an important role in the diagnosis and treatment of glaucoma.