Central corneal thickness and corneal hysteresis associated with glaucoma damage

Heartbeat-Induced Corneal Axial Displacement and Strain Measured by High Frequency Ultrasound Elastography in Human Volunteers

Purpose

The purpose of this study was to establish in vivo data acquisition and processing protocols for repeatable measurements of heartbeat-induced corneal displacements and strains in human eyes, using a high-frequency ultrasound elastography method, termed ocular pulse elastography (OPE).

Methods

Twenty-four volunteers with no known ocular diseases were recruited for this study. Intraocular pressure (IOP) and ocular pulse amplitude (OPA) were measured using a PASCAL Dynamic Contour Tonometer (DCT). An in vivo OPE protocol was developed to measure heartbeat-induced corneal displacements. Videos of the central 5.7 mm of the cornea were acquired using a 50-MHz ultrasound probe at 128 frames per second. The radiofrequency data of 1000 frames were analyzed using an ultrasound speckle tracking algorithm to calculate corneal displacements and quantify spectral and temporal characteristics. The intrasession and intersession repeatability of OPE- and DCT-measured parameters were also analyzed.

Results

The in vivo OPE protocol and setup were successful in tracking heartbeat-induced corneal motion using high-frequency ultrasound. Corneal axial displacements showed a strong cardiac rhythm, with good intrasession and intersession repeatability, and high interocular symmetry. Corneal strain was calculated in two eyes of two subjects, showing substantially different responses.

Conclusions

We demonstrated the feasibility of high-frequency ultrasound elastography for noninvasive in vivo measurement of the cornea's biomechanical responses to the intrinsic ocular pulse. The high intrasession and intersession repeatability suggested a robust implementation of this technique to the in vivo setting.

Translational Relevance

OPE may offer a useful tool for clinical biomechanical evaluation of the cornea by quantifying its response to the intrinsic pulsation.

Study of corneal biomechanical properties in patients with childhood glaucoma

AIM

To study of corneal biomechanical properties and intraocular pressure (IOP) measured with Corvis Scheimpflug Technology (ST) in patients with childhood glaucoma (CG).

METHODS

Cross-sectional study in which 89 eyes were included 56 of them with CG. Only one eye per patient was included. The following variables were obtained from the clinical history and the ophthalmological examination: age, sex, IOP, number of surgeries, and the cup/disc ratio (CDR). The following parameters were recorded using Corvis ST: corrected by biomechanics IOP (bIOP), not corrected IOP (nctIOP), central corneal thickness (CCT), maximum concavity [radius, peak distance (PD) and deformation amplitude], applanation 1 and 2 (length and velocity). The mean age was 23±14.55 and 33±19.5 years old for the control group and CG group, respectively. Totally 36 were males and 53 were females. In the CG group, 7 patients were controlled only with medical treatment. Sixteen had at least one previous goniotomy, 19 had at least one trabeculectomy, and 11 had an Ahmed implant.

RESULTS

A significant and positive intraclass correlation coefficient was found between Goldman IOP and the IOP measured by Corvis in both groups. No differences were found between the IOP measured with Corvis and Goldman using a student t-test. Regarding biomechanical parameters, there were differences in the applanation length 2 (A-L2), in the applanation velocity 2 (A-V2) and in the PD. By sex, only the applanation length 1 (A-L1) was found to be different in control group. A positive and significant Pearson correlation was found between CDR and the A-L1.

CONCLUSION

Corneal biomechanical properties have shown differences between CG and healthy subjects and also between men and women.

Relationship between corneal stiffness parameters and lamina cribrosa curvature in normal tension glaucoma

PURPOSE

To evaluate the relationship between corneal biomechanical parameters and lamina cribrosa (LC) curvature in normal tension glaucoma (NTG).

METHODS

95 eyes of 56 NTG patients were enrolled in this prospective, observational study. Corneal biomechanical parameters, including stiffness parameters at applanation 1 (SP-A1), deformation amplitude ratio (DA ratio), inverse concave radius and biomechanically corrected intraocular pressure estimate (bIOP), were captured using the Corneal Visualization Scheimpflug Technology instrument (Corvis-ST). LC curvature was evaluated by mean adjusted LC curvature index (maLCCI) averaged by the measurements on 12 radial B-scan images obtained using swept-source optical coherence tomography (SS-OCT). Linear mixed models were constructed to assess the relationship between corneal biomechanical parameters and LC curvature.

RESULTS

The mean age of participants was 51.04 ± 13.74 years (range, 24-82 years). The SP-A1 and maLCCI were 93.50 ± 13.82 mm Hg/mm and 7.57 ± 1.58, respectively. In univariate and multivariate analysis, SP-A1 (p < 0.001 and p = 0.001) and age (p = 0.010 and p = 0.024) were both significantly associated with maLCCI. The LC curvature increased with softer cornea demonstrated by lower SP-A1 and younger eyes. There was no statistical significance interaction between SP-A1 and age (p = 0.194).

CONCLUSIONS

The greater posterior LC curvature was associated with lower corneal stiffness parameters and younger eyes in NTG patients.

CLINICAL TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR1900021465.

The Relationship Between Corvis ST Tonometry Parameters and Ocular Response Analyzer Corneal Hysteresis

PRECIS

Corvis ST Tonometry and Ocular Response Analyzer (ORA) measurements were conducted in primary open-angle glaucoma and normative subjects. Many parameters were significantly correlated, however, the strengths were weak to moderate.

PURPOSE

Reichert ORA parameters are derived from pressure information following the application of air-jet, whereas detailed structural observation can be made using the Corneal Visualization Scheimpflug Technology instrument (CST). The purpose of the study was to investigate the association between CST measurements and ORA measured corneal hysteresis (CH).

METHODS

Measurements of CST, ORA, axial length, average corneal curvature, central corneal thickness (CCT) and intraocular pressure with Goldmann applanation tonometry were carried out in 104 eyes of 104 patients with primary open-angle glaucoma and 35 eyes from normative subjects. The association between CST and ORA parameters was assessed using linear regression analysis, with model selection based on the second order bias corrected Akaike Information Criterion index.

RESULTS

Deformation amplitude ratio (corneal softness, R=-0.51), SP A1 (corneal stiffness, R=0.41), and Inverse Radius (integrated area under the curve of the inverse concave radius, R=-0.44) were significantly correlated with CH (P <0.05). The optimal model to explain CH using CST measurements was given by: CH=-76.3+4.6×A1 time (applanation time in the corneal inward movement)+1.9×A2 time (second applanation time in the corneal outward movement) + 3.1 × highest concavity deformation amplitude (magnitude of movement of the corneal apex from before deformation to its highest concavity) + 0.016×CCT (R=0.67; P<0.001).

CONCLUSIONS

CST parameters are significant, but weakly or moderately, related to ORA measured CH.

Biomechanical properties of the cornea following intravitreal ranibizumab injection

OBJECTIVE

To evaluate intraocular pressure (IOP) and corneal biomechanical properties changes after intravitreal ranibizumab injection (IVRI).

METHODS

One hundred twenty eyes of 120 patients who underwent IVRI between January and March 2018 in Adnan Menderes University Ophthalmology Clinic were included in study. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated intraocular pressure (IOPcc) were measured by Ocular Response Analyzer (ORA) by the same specialist preoperatively (preop), postoperative 1st (postop-1st), postoperative 3rd (postop-3rd), and postoperative 24th hours (postop-24th) after single-dose IVRI.

RESULTS

Among the 120 wet age-related macular degeneration subjects, 58 (48.3%) were female and 62 (51.7%) were male. The mean age was 64.8 ± 10.4 years. Postop-1st hour IOP cc and IOPg measurements were statistically different from all other measurements (p < 0.001). Postop-1st hour CH measurements were statistically different from preop and postop-3rd (p = 0.022 and p = 0.008, respectively).

CONCLUSION

After intravitreal injection, IOP pressures significantly increased. But, CH and CRF values were significantly decreased. All these changes were temporary.

Association of 24-Hour Intraocular Pressure Fluctuation With Corneal Hysteresis and Axial Length in Untreated Chinese Primary Open-Angle Glaucoma Patients

PURPOSE

The purpose of this study was to evaluate the association of 24-hour intraocular pressure (IOP) fluctuation with corneal biomechanics and ocular biometric parameters in Chinese patients with primary open angle glaucoma (POAG) before initial treatment.

METHODS

Forty-nine Chinese patients with POAG (98 eyes) were recruited in this study before start of any POAG treatment. The 24-hour IOP was measured with a 2-hour interval by a noncontact tonometer. Corneal biomechanical properties and biometric parameters were measured once during 8 AM to 6 PM before 24-hour IOP measurement.

RESULTS

The 24-hour IOP fluctuation was defined as the differences between the peak and trough IOP measurement and was significantly associated with axial length (AL) in the multivariate analysis. The POAG subjects with AL ≤ 26 mm had significantly larger 24-hour IOP fluctuation but lower corneal hysteresis, compared to those with AL > 26 mm. In addition, subgroup analysis showed that high tension glaucoma subjects had larger 24-hour IOP fluctuation and higher corneal resistance factor than patients with normal tension glaucoma.

CONCLUSIONS

This study revealed the association of 24-hour IOP fluctuation with office hour corneal biomechanical properties and AL in patients with POAG. Their contributions to IOP fluctuation should be considered in the risk analysis of glaucoma development and progression.

TRANSLATIONAL RELEVANCE

Ocular biometric parameters are related with 24-hour IOP fluctuation in patients with POAG, which is potentially helpful in explaining different progression patterns in different types of patients.

The changes of corneal biomechanical properties with long-term treatment of prostaglandin analogue measured by Corvis ST

BACKGROUND

To investigate the corneal biomechanical changes in primary open angle glaucoma (POAG) patients treated with long-term prostaglandin analogue (PGA).

METHODS

One hundred eleven newly diagnosed POAG patients, including 43 high tension glaucoma (HTG) and 68 normal tension glaucoma (NTG), were measured by Corvis ST to obtain intraocular pressure (IOP), central corneal thickness (CCT) and corneal biomechanical parameters at baseline and at each follow-up visit after initiation of PGA treatment. The follow-up measurements were analyzed by the generalized estimate equation model with an exchangeable correlation structure. Restricted cubic spline was employed to estimate the dose-response relation between follow-up time and corneal biomechanics.

RESULTS

The mean follow-up time was 10.3 ± 7.02 months. Deformation amplitude (β = -0.0015, P = 0.016), the first applanation velocity (AV1, β = -0.0004, P = 0.00058) decreased and the first applanation time (AT1, β = 0.0089, P < 0.000001) increased statistically significantly with PGA therapy over time after adjusting for age, gender, axial length, corneal curvature, IOP and CCT. In addition, AT1 was lower (7.2950 ± 0.2707 in NTG and 7.5889 ± 0.2873 in HTG, P = 0.00011) and AV1 was greater (0.1478 ± 0.0187 in NTG and 0.1314 ± 0.0191 in HTG, P = 0.00002) in NTG than in HTG after adjusting for confounding factors.

CONCLUSIONS

Chronic use of PGA probably influences the corneal biomechanical properties directly, which is to make cornea less deformable. Besides, corneas in NTG tended to be more deformable compared to those in HTG with long-term treatment of PGA.

Dynamic Scheimpflug Ocular Biomechanical Parameters in Untreated Primary Open Angle Glaucoma Eyes

Purpose

To characterize the corneal biomechanical properties of glaucoma eyes by comparing the dynamic Scheimpflug biomechanical parameters between untreated glaucoma and control eyes.

Methods

Cross-sectional observational data of dynamic Scheimpflug analyzer (Corvis ST) examinations were retrospectively collected from 35 eyes of 35 consecutive patients with untreated normal tension glaucoma and 35 eyes of 35 healthy patients matched on age and IOP. Ten biomechanical parameters were compared between the two groups using multivariable models adjusting for IOP, central corneal thickness, age, and axial length. The Benjamini-Hochberg method was used to correct for multiple comparison.

Results

In multivariable models, glaucoma was associated with smaller applanation 1 time (P < 0.001, coefficient = −0.5865), applanation 2 time (P = 0.012, coefficient = −0.1702), radius (P = 0.006, coefficient = −0.5447), larger peak distance (P = 0.011, coefficient = 0.1023), deformation amplitude ratio at 1 mm (P < 0.001, coefficient = 0.072), and integrated radius (P < 0.001, coefficient = 1.094). These associations consistently indicate greater compliance of the cornea in glaucoma eyes.

Conclusions

Untreated normal tension glaucoma eyes were more compliant than healthy eyes. The greater compliance (smaller stiffness) of normal tension glaucoma eyes may increase the risk of optic nerve damage. These results suggest the relevance of measuring biomechanical properties of glaucoma eyes.

Baseline structural characteristics of the optic nerve head and retinal nerve fiber layer are associated with progressive visual field loss in patients with open-angle glaucoma

Aims

To examine the relationship between baseline structural characteristics of the optic nerve head (ONH) and retinal nerve fiber layer (RNFL) and functional disease progression in patients with open-angle glaucoma (OAG) over 5 years.

Methods

112 OAG patients were prospectively examined at baseline and every 6 months over a period of five years. Structural glaucomatous changes were examined with optical coherence tomography (OCT) and Heidelberg retinal tomography-III (HRT-III), and functional disease progression with automated perimetry (Humphrey visual fields). Cox proportional hazard models were used to assess the relationship between baseline structural measurements and functional disease progression.

Results

From baseline over a 5-year period, statistically significant increases were found in OCT disc (D) area (p<0.001), cup (C) area (p<0.001), C/D area ratio (p<0.001), C/D horizontal ratio (p<0.001), C/D vertical ratio (p = 0.018), and a decrease in superior RNFL thickness (p = 0.008). Statistically significant increases were found in HRT-III C volume (p = 0.021), C/D area ratio (p = 0.046), mean C depth (p = 0.036), C shape (p = 0.008), and height variation contour (p = 0.020). Functional disease progression was detected in 37 of the 112 patients (26 of European descent and 11 of African descent; 33%). A statistically significant shorter time to functional progression was seen in patients with larger baseline OCT D area (p = 0.008), C area (p = 0.003), thicker temporal RNFL (p = 0.003), and in patients with a larger HRT-III C area (p = 0.004), C/D area ratio (p = 0.004), linear C/D ratio (p = 0.007), C shape (p = 0.032), or smaller rim area (p = 0.039), rim volume (p = 0.005), height variation contour (p = 0.041), mean RNFL thickness (p<0.001), or RNFL cross-sectional area (p = 0.002).

Conclusion

Baseline ONH and RNFL structural characteristics were associated with a significantly shorter time to functional glaucomatous progression and visual field loss through the five-year period in OAG patients.

Corneal Hysteresis as a Biomarker of Glaucoma: Current Insights

The diagnosis and management of glaucoma has long been dependent on making decisions based on family history, optic nerve head evaluation, intraocular pressure, visual field testing, and optical coherence testing. Other pieces to aid in understanding glaucoma have presented throughout the years, including the role of corneal thickness. The discussion and debate on the mechanism of glaucoma have been attributed to resistance at the level of the conventional outflow pathway, perfusion pressure to the optic nerve head, cerebral spinal fluid pressure, and many more. Another piece that has emerged is corneal hysteresis, an assessment of the cornea’s ability to absorb and dissipate energy. There is abundant published literature supporting corneal hysteresis being associated with the presence and severity of glaucoma, the structural and functional progression of glaucoma, and the conversion to glaucoma. The supported data in these studies add another piece, corneal hysteresis, to consider in the diagnosis and management of glaucoma.

The Relationship Between Asymmetries of Corneal Properties and Rates of Visual Field Progression in Glaucoma Patients

PRéCIS:: In this study, asymmetries in corneal hysteresis (CH) between eyes of glaucoma patients were significantly associated with asymmetries in rates of visual field loss, suggesting a role of hysteresis as a risk factor for disease progression.

PURPOSE

The purpose of this study was to investigate the relationship between asymmetries in rates of glaucoma progression and asymmetries of corneal properties between eyes of subjects with primary open-angle glaucoma.

PARTICIPANTS AND METHODS

This prospective study followed 126 binocular subjects with glaucoma for an average of 4.3±0.8 years. CH was measured at baseline using the Ocular Response Analyzer. Standard automated perimetry (SAP) and intraocular pressure were measured at baseline and every 6 months. Rates of visual field progression were calculated using ordinary least square regression of SAP mean deviation (MD) values over time for each eye. Eyes were defined as "better" and "worse" based on the slopes of SAP MD. Pearson correlation test, and univariable and multivariable regression models were used to investigate the relationship between inter-eye asymmetry in CH and central corneal thickness and inter-eye differences in rates of visual field progression.

RESULTS

Only asymmetry of CH was significantly associated with the asymmetry in SAP MD rates of change between eyes (r=0.22; P=0.01). In a multivariable model adjusting for age, race, central corneal thickness, mean intraocular pressure and baseline disease severity, CH asymmetry remained significantly associated with asymmetric progression (P=0.032).

CONCLUSION

CH asymmetry between eyes was associated with asymmetry on rates of visual field change, providing further support for the role of CH as a risk factor for glaucoma progression.

Interocular Asymmetry of Visual Field Loss, Intraocular Pressure and Corneal Parameters in Primary Open-angle Glaucoma

OBJECTIVES

To assess the association between the corneal biomechanical parameters and visual field (VF) loss in patients with asymmetric primary open-angle glaucoma (POAG).

METHODS

A total of 89 POAG patients (50 males, 56.2%) with asymmetric VF loss, aged 65.2 ± 13.3 years old, were enrolled in this study. Asymmetric VF loss was defined as an interocular difference of the global index mean deviation (MD) >2dB. Intraocular pressure (IOP), central corneal thickness (CCT) and corneal biomechanical parameters such as maximum amplitude at the apex of highest concavity (Def ampl HC) were measured. The worse eye was defined as the eye with a smaller MD.

RESULTS

The worse eyes had lower MD (-11.9 ± 6.7 dB vs. -5.3 ± 5.0 dB; P<0.001) and higher IOP (14.6 ± 3.3 vs.13.9 ± 2.6 mmHg, P=0.04) than the better eyes. There was no significant difference between the two groups for CCT. The interocular difference of MD (IDMD) was negatively correlated with the interocular difference of IOP (r=-0.22, P=0.04), while positively correlated with the interocular difference of Def ampl HC (r=0.27, P=0.01). In patients with moderate asymmetric VF loss (IDMD ≥6 dB), the Def ampl HC of the worse eyes group (1.07 ± 0.12 mm) were significantly lower than the better eyes group (1.10 ± 0.11 mm, p=0.02).

CONCLUSION

Asymmetric POAG was associated with asymmetry in IOP and corneal biomechanical parameters but not in CCT. Lower deflection amplitude and higher IOP was found in eyes with more severe visual field damage in POAG patients.

Corneal Stiffness and Collagen Cross-Linking Proteins in Glaucoma: Potential for Novel Therapeutic Strategy

Biomechanical properties of the cornea have recently emerged as clinically useful in risk assessment of diagnosing glaucoma and predicting disease progression. Corneal hysteresis (CH) is a dynamic tool, which measures viscoelasticity of the cornea. It represents the overall deformability of the cornea, and reduces significantly with age. Low CH has also been associated with optic nerve damage and progression of visual field loss in glaucoma. The extracellular matrix (ECM) constituents of the cornea, trabecular meshwork (TM), sclera, and lamina cribrosa (LC) are similar, as they are predominantly made of fibrillar collagen. This suggests that biomechanical changes in the cornea may also reflect optic nerve compliance in glaucomatous optic neuropathy, and in the known increase of TM tissue stiffness in glaucoma. Increased collagen cross-linking contributes to tissue stiffening throughout the body, which is observed in normal aging and occurs at an accelerated rate in systemic conditions such as fibrotic and cardiovascular diseases, cancer, and glaucoma. We reviewed 3 ECM cross-linking proteins that may have a potential role in the disease process of increased tissue stiffness in glaucoma, including lysyl oxidase (LOX)/lysyl oxidase-like 1 (LOXL1), tissue transglutaminase (TG2), and advanced glycation end products. We also report elevated messenger RNA (mRNA) levels of LOX and TG2 in glaucoma LC cells to support our proposed theory that increased levels of cross-linking proteins in glaucoma play a role in LC tissue stiffness. We highlight areas of research that are needed to better understand the role of cross-linking in glaucoma pathogenesis, leading potentially to a novel therapeutic strategy.

Visualizing the dynamic change of Ocular Response Analyzer waveform using Variational Autoencoder in association with the peripapillary retinal arteries angle

The aim of the current study is to identify possible new Ocular Response Analyzer (ORA) waveform parameters related to changes of retinal structure/deformation, as measured by the peripapillary retinal arteries angle (PRAA), using a generative deep learning method of variational autoencoder (VAE). Fifty-four eyes of 52 subjects were enrolled. The PRAA was calculated from fundus photographs and was used to train a VAE model. By analyzing the ORA waveform reconstructed (noise filtered) using VAE, a novel ORA waveform parameter (Monot1-2), was introduced, representing the change in monotonicity between the first and second applanation peak of the waveform. The variables mostly related to the PRAA were identified from a set of 41 variables including age, axial length (AL), keratometry, ORA corneal hysteresis, ORA corneal resistant factor, 35 well established ORA waveform parameters, and Monot1-2, using a model selection method based on the second-order bias-corrected Akaike information criterion. The optimal model for PRAA was the AL and six ORA waveform parameters, including Monot1-2. This optimal model was significantly better than the model without Monot1-2 (p = 0.0031, ANOVA). The current study suggested the value of a generative deep learning approach in discovering new useful parameters that may have clinical relevance.

Effect of trabeculectomy and Ahmed glaucoma valve implantation surgery on corneal biomechanical changes

PURPOSE

To evaluate alterations in corneal biomechanical properties before and 6 months after conventional trabeculectomy (TRAB) and Ahmed glaucoma valve (AGV) implantation.

METHODS

Thirty-nine eyes of 39 patients were evaluated retrospectively. Complete ophthalmological examinations including evaluation of corneal biomechanical properties using the Ocular Response Analyzer were performed before and after 6 months postoperatively. A mean of four measurements for corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOPg), and corneal compensated intraocular pressure (IOPcc) was recorded. The participants had undergone trabeculectomy or shunt surgery as the first surgical procedure for glaucoma treatment of uncontrolled IOP with maximum antiglaucoma eyedrops.

RESULTS

There were 20 eyes of 20 patients in trabeculectomy group and 19 eyes of 19 patients in AGV implantation group. There was no significant difference between two groups in terms of sex, age, eye laterality, lens status, antiglaucoma drug usage, preoperatively measured Mean Deviation of Humphrey Visual Field Analyzer, CH, CRF, IOPcc, and IOPg (p > 0.05). CH and CRF increased significantly after shunt surgery (p < 0.001). CH increased in trabeculectomy group postoperatively (p < 0.001); however, CRF showed a small amount of decrease, but this reduction was not statistically significant (p > 0.05). CH and CRF showed higher increase after AGV surgery than trabeculectomy surgery (p < 0.05). There was no significant correlation between IOP changes and CH-CRF changes in both TRAB and AGV groups (p > 0.05).

CONCLUSION

According to our results, surgical technique differences may have an impact on postoperative corneal biomechanical outcomes. AGV surgery offers better corneal biomechanical results than standard trabeculectomy in 6-month follow-up.

Relationship of Corneal Hysteresis and Anterior Lamina Cribrosa Displacement in Glaucoma

PURPOSE

To investigate the relationship between corneal hysteresis (CH) and anterior lamina cribrosa surface (ALCS) displacement over time in a cohort of patients with glaucoma.

DESIGN

Prospective observational case series.

METHODS

In this study, 147 eyes from 96 glaucoma or glaucoma suspect patients were followed for a mean of 3.5 years and 7.9 visits. Baseline CH measurements were obtained using the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments Inc, Depew, New York, USA). The mean anterior lamina cribrosa surface depth (ALCSD) and choroidal thickness were by automated segmentation of spectral-domain optical coherence tomography (SD-OCT) scans. The rate of change of ALCSD was calculated using linear mixed effects models. Relationship between baseline CH and follow-up ALCSD rate of change was adjusted for confounding factors, including age, intraocular pressure (IOP), and choroidal thickness.

RESULTS

The mean baseline CH was 9.4 mm Hg (95% confidence interval [CI] 9.1-9.7). Overall, the ALCS was displaced posteriorly at a rate of 0.78 μm/y (95% CI -1.82, 0.26). Seventeen eyes (11.5%) showed a significant posterior displacement of ALCS, whereas 22 eyes (15.0%) showed a significant anterior displacement of ALCS. The choroidal thickness thinned at a rate of -1.09 μm/y during the follow-up (P = .001). Multivariable mixed modeling showed that choroidal thinning, lower IOP change, and lower corneal hysteresis were significantly associated with posterior ALCS displacement over time (P = .034, P = .037, and P = .048). Each 1 mm lower CH was associated with 0.66 μm/y posterior displacement of the ALCS.

CONCLUSIONS

Lower corneal hysteresis was significantly associated with posterior displacement of the anterior lamina cribrosa over time. These data provide additional support for lower corneal hysteresis being a risk factor for glaucoma progression.

Association Between Lamina Cribrosa Defects and Progressive Retinal Nerve Fiber Layer Loss in Glaucoma

Importance

Certain features of the lamina cribrosa may be associated with increased risk of glaucoma progression.

Objectives

To compare the rates of retinal nerve fiber layer (RNFL) thinning in patients with open-angle glaucoma with or without lamina cribrosa (LC) defects and to evaluate factors associated with the rate of glaucoma progression in eyes with LC defects.

Design, Setting, and Participants

This longitudinal cohort study designed in September 2017 and conducted at a tertiary glaucoma center in California included 51 eyes of 43 patients with LC defects and 83 eyes of 68 patients without LC defects followed up for a mean (SD) of 3.5 (0.8) years from April 2012 to May 2017.

Main Outcomes and Measures

Focal LC defects were detected using swept-source optical coherence tomographic images. All participants underwent visual field testing and spectral-domain optical coherence tomography for RNFL thickness measurements every 6 months. Univariate and multivariable random-effects models were used to compare the rate of local and global RNFL loss.

Results

The mean (95% CI) age at baseline for individuals with LC defects was 69.5 (65.4 to 73.6) years, and for those without LC defects, it was 69.6 (67.2-72.0) years; 18 individuals (41%) with LC defects and 35 individuals (51%) without LC defects were men; 6 individuals (14%) with LC defects and 17 individuals (25%) without were African American. The mean (95% CI) rate of global RNFL loss in eyes with LC defects was 2-fold faster than that in eyes without LC defects (-0.91 [-1.20 to -0.62] vs -0.48 [-0.65 to -0.31] μm/y; difference, -0.43 [-0.76 to -0.09] μm/y; P = .01). The rate of RNFL thinning was faster in the LC defect sectors than that in the unaffected sectors (difference, -0.90 [95% CI, -1.68 to -0.12] μm/y, P = .02). Thinner corneal thickness was the only factor that was associated with a faster rate of RNFL loss in eyes with LC defects (β2 = -0.09 [95% CI, -0.14 to -0.04], P = .001). No association was found between mean intraocular pressure during follow-up and the mean rate of RNFL thinning in eyes with LC defects (β2, -0.05 [95% CI, -0.17 to 0.06], P = .36).

Conclusions and Relevance

These data suggest that LC defects are an independent risk factor for RNFL thinning and that glaucoma progression may correspond topographically to the LC defect location. Thinner corneal thickness in eyes with LC defects was associated with faster further glaucoma progression. In the management of open-angle glaucoma, LC findings may inform the likelihood and rate of glaucoma progression.

Corneal biomechanical responses detected using corvis st in primary open angle glaucoma and normal tension glaucoma

Structural differences have been reported between primary open angle glaucoma (POAG) and normal tension glaucoma (NTG), and biomechanical differences between POAG and NTG may account for why NTG patients are more vulnerable to lower intraocular pressure (IOP). This study compared the biomechanical properties of POAG and NTG patients using the Corvis scheimpflug technology (ST) non-contact Scheimpflug-based tonometer, and determined the factors associated with these properties.In this retrospective cross-sectional study, 46 eyes with POAG, 54 eyes with NTG, and 61 control eyes were included. A non-contact Scheimpflug-based tonometer was used to examine and compare the corneal biomechanical responses in the POAG, NTG, and normal groups. We used univariate and multivariate regression analyses to determine the factors associated with the deformation amplitude in each group.Baseline characteristics, including age, IOP, spherical equivalent, keratometry, axial length, and central corneal thickness, were similar among the 3 groups. Severity of glaucoma, as measured by mean deviation, was similar between POAG and NTG groups. Applanation 1 velocity and deformation amplitude were significantly smaller in POAG (0.13 ± 0.02 and 1.06 ± 0.14, respectively) than NTG (0.14 ± 0.01 and 1.13 ± 0.11, respectively) and normal groups (0.14 ± 0.02 and 1.13 ± 0.10, respectively). Radius of curvature was significantly larger in the POAG group compared to the normal group. In normal controls, IOP and keratometry were significant factors related to deformation amplitude. In POAG eyes, IOP was a statistically significant predictor of deformation amplitude. In NTG eyes, however, IOP , keratometry, and axial length were statistically significant predictors of deformation amplitude.POAG eyes showed less deformable corneas compared to NTG and normal controls. IOP was significantly correlated with deformation amplitude in all groups. However, axial length was positively correlated with deformation amplitude only in NTG eyes. Characterization of the differences in biomechanical properties between POAG and NTG may contribute to a better understanding of the underlying pathophysiologies associated with these diseases.

Association of Corneal Hysteresis With Lamina Cribrosa Curvature in Primary Open Angle Glaucoma

Purpose

To investigate whether corneal biomechanical properties are associated with the lamina cribrosa (LC) curvature in eyes with primary open angle glaucoma (POAG).

Methods

Corneal biomechanical properties and LC curvature were assessed in 65 treatment-naïve POAG patients. Corneal biomechanical properties, including corneal hysteresis (CH), corneal resistance factor (CRF), and corneal-compensated intraocular pressure (IOPcc), were measured using an ocular response analyzer (ORA; Reichert Ophthalmic Instruments). LC curvature was assessed by measuring the LC curvature index (LCCI) on B-scan images obtained using spectral-domain optical coherence tomography (OCT). The LCCI was determined by measuring LC curve depth on the anterior LC surface and the width of the reference line.

Results

The LCCI was correlated with CH (P = 0.001), CRF (P = 0.012) and IOPcc (P = 0.001) in the univariate analysis. To adjust multicollinearity, principal component analysis was performed, and multivariate regression analyses were conducted using one variable from each component. The larger LCCI was associated with larger IOPcc (P < 0.001), smaller CRF (P = 0.001) and smaller CH (P < 0.001).

Conclusions

Lower CH was associated with a more posteriorly curved LC in treatment naïve POAG patients. This finding may provide a basic explanation for the reported association between CH and an increased risk for glaucoma development and progression, and support a potential value of CH for risk assessment for glaucoma.

[Biomechanical properties of the cornea as predictors of the effectiveness of selective laser trabeculoplasty]

PURPOSE

To study the changes in central corneal thickness (CCT) and corneal hysteresis (CH) after selective laser trabeculoplasty (SLT) in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG) after laser peripheral iridotomy (LPI) and to determine their effect on the prognosis of the surgery.

MATERIAL AND METHODS

The prospective study involved 68 eyes with initial PACG after LPI and 74 eyes with initial POAG observed for 6 months. Corneal-compensated IOP (IOPcc), corneal resistance factor (CRF), CH and CCT were studied as the predictors of SLT, which was considered successful when IOPcc decreased by 20% or more from the baseline without additional hypotensive therapy and/or repeated SLT.

RESULTS

In both forms of glaucoma, CCT increased within the first hour after SLT: 567±24.08 µm (p=0.001) in POAG, and 572±21.41 µm (p=0.000) - persisting for over a month - in PACG. CCT correlated with laser energy at all stages of the examination both in POAG and PACG patients. The following predictors of SLT failure were determined: CH (p=0.000 in PACG and p=0.001 in POAG), as well as initial IOP (p=0.010 in PACG and p=0.016 in POAG) and CRF (p=0.003 in PACG and p=0.005 in POAG) and CCT (p=0.023 in PACG and p=0.026 in POAG). The value of anterior chamber angle (ACA) was a predictor only for PACG (p=0.011).

CONCLUSION

SLT leads to an increase in CCT, which lasts longer in PACG after LPI than in POAG and correlates with the level of laser energy. Lower CH and initially higher IOP are the common predictors of SLT failure in the long term for both forms of glaucoma. Smaller ACA have a negative prognostic sign in POAG.

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.

Relationship between optic disc hemorrhage and corneal hysteresis

OBJECTIVE

To determine the relationship between optic disc hemorrhage (DH) and corneal hysteresis (CH).

METHODS

Consecutive patients with prior or current photographic evidence of unilateral DH who had undergone CH measurement with the Ocular Response Analyzer (ORA; Reichert, Buffalo, NY) were enrolled. Eyes with a history of corneal disease, refractive surgery, or bilateral DH were excluded. Central corneal thickness (CCT), visual field data, 5 consecutive previous intraocular pressures (IOPs), and maximum documented peak IOP were obtained by chart review. Vertical cup-to-disc ratio (VCDR), the presence of neuroretinal rim notching, number of clock hours of beta zone parapapillary atrophy (ßPPA), and eye with greater ßPPA width were determined from photographs by 2 masked expert examiners.

RESULTS

We identified and analyzed 49 patients with photographically documented unilateral DH. Compared to fellow non-DH eyes, eyes with DH had lower CH (8.7 ± 1.9 vs 9.2 ± 1.7; p = 0.002), higher IOP (15.6 ± 3.6 vs 14.3 ± 4.1; p = 0.017), and greater VCDR (0.79 ± 0.13 vs 0.68 ± 0.23; p < 0.001), but were similar with respect to CCT, ßPPA extent, rim notching, peak IOP, and visual field damage (all p > 0.05). Using multivariate conditional logistic regression analysis, only CH (p = 0.012) and VCDR (p = 0.004) predicted the laterality of the DH.

CONCLUSIONS

Lower CH and greater VCDR are independently associated with DH. This suggests that CH may be a structural biomarker for an abnormality of the optic nerve complex that may be associated with progressive glaucoma. Eyes in which DH were detected had lower CH.

Effects of vitamin D deficiency on intraocular pressure values obtained by ocular response analyzer

PURPOSE

To compare corneal biomechanical properties measured with ocular response analyzer (ORA) and intraocular pressure (IOP) measurements in patients with vitamin D deficiency and in healthy cases.

METHODS

One hundred and twenty eyes of 120 subjects (between the ages of 19 and 78) who applied to university's outpatient clinic were evaluated: 41 lacks of vitamin D (Group 1), 39 insufficient vitamin D (Group 2) and 40 controls (Group 3). Corneal hysteresis, corneal resistance factor, Goldmann-correlated IOP and corneal compensated IOP of patients were measured by ORA.

RESULTS

The mean ages were 48.9 ± 12.1, 52.8 ± 13.6 and 52.1 ± 13.9 in groups 1, 2 and 3, respectively (p = 0.370). Mean IOPcc values were 16.5 ± 3.6 (8.1-27.3), 16.7 ± 2.7 (12.0-22.7) and 16.3 ± 3.3 (10.8-27.4) mmHg (p = 0.889); mean IOPg values were 16.8 ± 5.0 (6.5-39.5), 16.3 ± 2.9 (10.3-23.0) and 15.9 ± 3.2 (10.0-26.0) mmHg (p = 0.539); mean CH values were 10.8 ± 1.9 (8.3-19.0), 11.4 ± 1.6 (6.9-14.0) and 11.2 ± 1.5 (7.5-13.2) (p = 0.257); mean CRF values were 10.5 ± 2.7 (7.4-25.0), 11.1 ± 1.5 (6.8-13.5) and 10.5 ± 1.2 (7.7-12.8) (p = 0.282) in groups 1, 2 and 3, respectively. There was no statistical difference between the groups in terms of IOPcc, IOPg CH and CRF. However, mean CH values were found less in the lack of vitamin D group.

CONCLUSION

The CH values were lower, and the IOPg values were higher in cases of vitamin D deficiency. Corneal biomechanical differences in patients with lack of vitamin D were not statistically significant.

Comparison of Corneal Biomechanics Between Low and High Myopic Eyes-A Meta-analysis

PURPOSE

To compare the corneal biomechanical difference between the low myopic eyes and high myopic eyes.

DESIGN

Systematic review and meta-analysis.

METHODS

Data sources, including PubMed, Medline, EMBASE, Web of Science, and Chinese databases including Wanfang and China National Knowledge Infrastructure, were searched to find the relevant studies. Primary outcomes were corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc), Goldmann-correlated intraocular pressure (IOPg), and central corneal thickness (CCT) in high myopic eyes and low myopic eyes.

RESULTS

Eleven studies were enrolled in this study. CH and CRF were significantly higher in the low myopic eyes. The mean difference of CH was 0.73 mm Hg, 95% confidence interval (CI) [0.53 to 0.93], P < .001. The mean difference of CRF was 0.20 mm Hg, 95% CI [0.04 to 0.37], P = .02. The IOPcc and IOPg were significantly lower in the low myopic eyes. The mean difference of IOPcc was -2.53 mm Hg, 95% CI [-3.24, -1.83], P < .01. The mean difference of IOPg was -1.42 mm Hg, 95% CI [-2.26, -0.58], P = .0009. There was no significant difference between the 2 groups on CCT; the mean difference was -2.85 μm, 95% CI [-9.64.3.93], P = .41.

CONCLUSION

Corneal biomechanics are different in the high myopic eyes. Low CH and CRF and high IOPcc and IOPg are suggested to be associated factors for high myopia. Future studies are needed to investigate the underlying corneal structure difference that causes the low CH and CRF value in the high myopic eyes.

Corneal deflection amplitude and visual field progression in primary open-angle glaucoma

Purpose

To investigate the relationship between corneal deflection amplitude and visual field progression rate in patients with primary open-angle glaucoma (POAG).

Methods

This study included 113 eyes of 65 patients with POAG followed for an average of 4.81 ± 1.24 years. Evaluation of visual field progression rate was performed using mean deviation of standard automated perimetry. Corneal deflection amplitude was measured using Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). Linear mixed models were performed to determine the relationship between corneal deflection amplitude, intraocular pressure (IOP), and visual field progression rate.

Results

Mean age was 56.36 ± 14.58 years. Baseline average mean deviation was -8.20 ± 9.12 dB and mean treated IOP was 14.38 ± 3.08 mmHg. Average deflection amplitude was 0.90 ± 0.13 mm. In both univariate and multivariate analysis, IOP (P = 0.028 and P < 0.001, respectively) and deflection amplitude (P = 0.034 and P < 0.001, respectively) significantly affected visual field progression rate. Eyes with high IOP and greater deflection amplitude showed faster progression rate.

Conclusions

Corneal deflection amplitude was significantly related with glaucoma progression. Eyes with greater corneal deflection amplitude showed faster visual field progression rate in patients with POAG.

Corneal Biomechanics and Visual Field Progression in Eyes with Seemingly Well-Controlled Intraocular Pressure

PURPOSE

To investigate the incidence and risk factors for glaucomatous visual field progression in eyes with well-controlled intraocular pressure (IOP).

DESIGN

Prospective cohort.

PARTICIPANTS

A total of 460 eyes of 334 patients with glaucoma under treatment.

METHODS

Study subjects had a mean follow-up of 4.3±0.8 years. Patients were classified as well controlled if all IOP measurements were less than 18 mmHg. Rates of visual field progression were calculated using ordinary least-squares linear regression of standard automated perimetry (SAP) mean deviation (MD) values over time. Progression was defined as a significantly negative MD slope (alpha = 0.05).

MAIN OUTCOME MEASURES

Rates of SAP MD change; mean and peak IOP, and IOP fluctuation; and corneal biomechanics: corneal hysteresis (CH), central corneal thickness (CCT), and corneal index.

RESULTS

Of the 179 eyes with well-controlled IOP, 42 (23.5%) demonstrated visual field progression. There was no significant difference between progressing and stable patients in baseline MD (-6.4±7.1 decibels [dB] vs. -6.0±6.2 dB; P = 0.346), mean IOP (11.7±2.0 mmHg vs. 12.1±2.3 mmHg; P = 0.405), IOP fluctuation (1.6±0.6 mmHg vs. 1.6±0.5 mmHg; P = 0.402), or peak IOP (14.3±1.9 mmHg vs. 14.6±2.1 mmHg; P = 0.926). Progressing eyes had significantly lower CH (8.6±1.3 mmHg vs. 9.4±1.6 mmHg; P = 0.014) and thinner CCT (515.1±33.1 μm vs. 531.1±42.4 μm; P = 0.018, respectively) compared with stable eyes. In the multivariate analysis, a 1 standard deviation lower corneal index, a summation of normalized versions of CH and CCT, resulted in a 68% higher risk of progression (odds ratio, 1.68; 95% confidence interval, 1.08-2.62; P = 0.021).

CONCLUSIONS

Approximately one-quarter of eyes with well-controlled IOP may show visual field progression over time. Thin cornea and low CH are main risk factors.

Associations with Corneal Hysteresis in a Population Cohort: Results from 96 010 UK Biobank Participants

PURPOSE

To describe the distribution of corneal hysteresis (CH) in a large cohort and explore its associated factors and possible clinical applications.

DESIGN

Cross-sectional study within the UK Biobank, a large cohort study in the United Kingdom.

PARTICIPANTS

We analyzed CH data from 93 345 eligible participants in the UK Biobank cohort, aged 40 to 69 years.

METHODS

All analyses were performed using left eye data. Linear regression models were used to evaluate associations between CH and demographic, lifestyle, ocular, and systemic variables. Piecewise logistic regression models were used to explore the relationship between self-reported glaucoma and CH.

MAIN OUTCOME MEASURES

Corneal hysteresis (mmHg).

RESULTS

The mean CH was 10.6 mmHg (10.4 mmHg in male and 10.8 mmHg in female participants). After adjusting for covariables, CH was significantly negatively associated with male sex, age, black ethnicity, self-reported glaucoma, diastolic blood pressure, and height. Corneal hysteresis was significantly positively associated with smoking, hyperopia, diabetes, systemic lupus erythematosus (SLE), greater deprivation (Townsend index), and Goldmann-correlated intraocular pressure (IOPg). Self-reported glaucoma and CH were significantly associated when CH was less than 10.1 mmHg (odds ratio, 0.86; 95% confidence interval, 0.79-0.94 per mmHg CH increase) after adjusting for covariables. When CH exceeded 10.1 mmHg, there was no significant association between CH and self-reported glaucoma.

CONCLUSIONS

In our analyses, CH was significantly associated with factors including age, sex, and ethnicity, which should be taken into account when interpreting CH values. In our cohort, lower CH was significantly associated with a higher prevalence of self-reported glaucoma when CH was less than 10.1 mmHg. Corneal hysteresis may serve as a biomarker aiding glaucoma case detection.

Corneal biomechanical changes after trabeculectomy with mitomycin C in primary open-angle glaucoma and pseudoexfoliation glaucoma

PURPOSE

This study aimed to examine the effect of trabeculectomy with mitomycin C on corneal biomechanical characteristics in PEXG and POAG patients.

METHODS

In this prospective comparative case series study, 32 glaucoma patients of whom 17 patients were suffering from PEXG and 15 patients from POAG were enrolled. All patients underwent complete ocular examination, CCT using ultrasound pachymetry and corneal biomechanical study using ORA. The patients were hospitalized, and trabeculectomy surgery with mitomycin was done. Three months after surgery, patients were examined and ORA was obtained again.

RESULTS

The mean CH in patients with PEXG was lower compared to patients with POAG (5.66 ± 1.13, 7.49 ± 0.88, respectively) before surgery, which had a statistically significant difference (P < 0.001). CRF in patients with PEXG was significantly lower compared to patients with POAG (8.19 ± 1.48 vs. 9.35 ± 1.60, respectively) before surgery, with P = 0.049. CH remarkably increased and reached 6.69 ± 0.78 (P < 0.001) in the PEXG group after TBX + MMC surgery. CH increased in the POAG group after TBX + MIC surgery and reached 8.23 ± 1.09, which was statistically significant (P = 0.001). There was a significant relationship between CH and IOP_g changes in both PEXG and POAG groups (P < 0.001 and P = 0.01, respectively). Although TBX + MMC surgery changed the amount of CH in PEXG and POAG groups, no significant difference was shown in the parameters between the two groups comparing the CH changes (P = 0.33).

CONCLUSION

According to the results of this study, the biomechanical characteristics of cornea, particularly CH, shows certain changes following surgery and is increased, reflecting the dynamic nature of these parameters. Our knowledge of the biomechanical changes after glaucoma surgery can help us better understand the pathophysiology of glaucoma diseases and make the right decisions for follow-up of the patients.

Rates of Visual Field Loss in Primary Open-Angle Glaucoma and Primary Angle-Closure Glaucoma: Asymmetric Patterns

Purpose

The purpose of this study was to evaluate the rate of visual field (VF) loss in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

Methods

Four hundred forty eyes of 282 patients with POAG (aged 53.4 ± 12.0: mean ± standard deviation, years) and 79 eyes of 49 patients with PACG (aged 62.7 ± 9.0 years) with at least six or more reliable VF tests were studied. Point-wise, region-wise, and global rates of VF change were assessed for POAG and PACG eyes. Only the VF records prior to laser iridotomy or cataract surgery were included in PACG eyes. The global and superior-inferior asymmetric rates of VF loss were compared between POAG and PACG eyes.

Results

The mean total deviation (mTD) values at baseline were -6.4 ± 5.7 dB in POAG patients and -6.4 ± 7.3 dB in PACG patients. There was not a significant difference in the progression rates of mTD between POAG eyes (-0.23 ± 0.38 dB/y) and PACG eyes (-0.29 ± 0.45 dB/y). In POAG eyes, the VF progression rate was significantly asymmetric across the horizontal line; the central, paracentral, and peripheral arcuate 2 regions in the superior hemifield had a significantly faster rate of VF loss than their inferior counterparts. In contrast, this asymmetry was not observed in the rate of VF loss in PACG eyes.

Conclusions

POAG eyes showed a faster rate of VF loss in the superior hemifield compared to in the inferior hemifield, particularly in central and paracentral regions. This difference was not observed in PACG eyes.

Line-Field Optical Coherence Tomography as a tool for In vitro characterization of corneal biomechanics under physiological pressures

There has been a lot of interest in accurately characterising corneal biomechanical properties under intraocular pressure (IOP) to help better understand ocular pathologies that are associated with elevated IOP. This study investigates the novel use of Line-Field Optical Coherence Tomography (LF-OCT) as an elastographic tool for accurately measuring mechanical properties of porcine corneas based on volumetric deformation following varying IOPs. A custom-built LF-OCT was used to measure geometrical and corneal surface displacement changes in porcine corneas under a range of IOPs, from 0-60 mmHg. Corneal thickness, elastic properties and hysteresis were calculated as a function of pressure. In addition, the effects of hydration were explored. We found that the elastic modulus increased in a linear fashion with IOP. Corneal thickness was found to reduce with IOP, decreasing 14% from 0 to 60 mmHg. Prolonged hydration in phosphate buffered saline (PBS) was found to significantly increase the elastic modulus and corneal hysteresis. Our study demonstrates that LF-OCT can be used to accurately measure the elastic properties based on volumetric deformation following physiological pressures. Furthermore, we show that prolonged hydration in PBS has a significant effect on the measured corneal properties.

Corneal biomechanics and biomechanically corrected intraocular pressure in primary open-angle glaucoma, ocular hypertension and controls

AIMS

To compare the biomechanically corrected intraocular pressure (IOP) estimate (bIOP) provided by the Corvis-ST with Goldmann applanation tonometry (GAT-IOP) in patients with high-tension and normal-tension primary open-angle glaucoma (POAG; HTG and NTG), ocular hypertension (OHT) and controls. Moreover, we compared dynamic corneal response parameters (DCRs) of the Corvis-ST in POAG, OHT and controls, evaluated the correlation between global visual field parameters mean deviation and pattern SD (MD and PSD) and DCRs in the POAG group.

METHODS

156 eyes of 156 patients were included in this prospective, single-centre, observational study, namely 41 HTG and 33 NTG, 45 OHT cases and 37 controls. Central corneal thickness (CCT), GAT-IOP and bIOP were measured, GAT-IOP was also adjusted for CCT (GATAdj). DCRs provided by Corvis-ST were evaluated, MD and PSD were recorded by 24-2 full-threshold visual field. To evaluate the difference in DCRs between OHT, HTG and NTG, a general linear model was used with sex, medications and group as fixed factors and bIOP and age as covariates.

RESULTS

There was a significant difference between GAT-IOP, GATAdj and bIOP in NTG and HTG, OHT and controls. NTG corneas were significantly softer and more deformable compared with controls, OHT and HTG as demonstrated by significantly lower values of stiffness parameters A1 and highest concavity and higher values of inverse concave radius (all p<0.05). There was a significant correlation (p<0.05) between MD, PSD and many DCRs with POAG patients with softer or more compliant corneas more likely to show visual field defects.

CONCLUSIONS

Corneal biomechanics might be a significant confounding factor for IOP measurement that should be considered in clinical decision-making. The abnormality of corneal biomechanics in NTG and the significant correlation with visual field parameters might suggest a new risk factor for the development or progression of NTG.

Novel dynamic corneal response parameters in a practice use: a critical review

Background

Non-contact tonometers based on the method using air puff and Scheimpflug’s fast camera are one of the latest devices allowing the measurement of intraocular pressure and additional biomechanical parameters of the cornea. Biomechanical features significantly affect changes in intraocular pressure values, as well as their changes, may indicate the possibility of corneal ectasia. This work presents the latest and already known biomechanical parameters available in the new offered software. The authors focused on their practical application and the diagnostic credibility indicated in the literature.

Discussion

An overview of available literature indicates the importance of new dynamic corneal parameters. The latest parameters developed on the basis of biomechanics analysis of corneal deformation process, available in non-contact tonometers using Scheimpflug’s fast camera, are used in the evaluation of laser refractive surgery procedures, e.g. LASIK procedure. In addition, the assessment of changes in biomechanically corrected intraocular pressure confirms its independence from changes in the corneal biomechanics which may allow an intraocular pressure real assessment. The newly developed Corvis Biomechanical Index combined with the corneal tomography and topography assessment is an important aid in the classification of patients with keratoconus.

Conclusion

New parameters characterising corneal deformation, including Corvis Biomechanical Index and biomechanical compensated intraocular pressure, significantly extend the diagnostic capabilities of this device and may be helpful in assessing corneal diseases of the eye. Nevertheless, further research is needed to confirm their diagnostic pertinence.

Development of a Novel Corneal Concavity Shape Parameter and Its Association with Glaucomatous Visual Field Progression

PURPOSE

To develop a novel Corvis ST (Oculus Co. Ltd, Wetzlar, Germany) corneal concavity shape parameter (concavity shape index [CSI]) and investigate its association with glaucomatous visual field (VF) progression.

DESIGN

Retrospective longitudinal study.

PARTICIPANTS

A total of 103 eyes with primary open-angle glaucoma in 68 patients with 8 reliable VFs using the Humphrey Field Analyzer (HFA) (Carl Zeiss Meditec Inc, Dublin, CA).

METHODS

The mean total deviation (mTD) of the 52 test points in the 24-2 HFA test pattern was calculated for each VF, and the mTD progression rate was determined. A Corvis ST measurement was performed, and CSI was calculated as the ratio of (peak distance × curvature radius at the time of highest concavity [HC] state) to (the deflection amplitude at the time of HC × curvature radius at the undeformed state). The association between mTD progression rate and CSI, as well as other variables (including age, intraocular pressure, corneal hysteresis [CH], and 35 standard Corvis ST parameters), was investigated using the linear mixed model. The optimal linear mixed model to describe mTD progression rate was selected using the Random Forest method followed by variable selection using the second order bias corrected Akaike Information Criterion (AICc) index.

MAIN OUTCOME MEASURES

Optimal linear mixed models for the mTD progression rate, as determined by AICc index.

RESULTS

Univariate analysis revealed mTD progression rate was significantly associated with CSI (P = 0.0042), CH, HC radius, A1 deflection length, max inverse radius, and integrated radius. The optimal model to describe mTD progression rate included CSI, max inverse radius, Ambrósio rational thickness horizontal, and age (AICc = 41.59).

CONCLUSIONS

A novel corneal concavity shape parameter, CSI, was closely related to glaucomatous VF progression.

Anterior Segment Biometry and Their Correlation with Corneal Biomechanics in Caucasian Children

PURPOSE

To assess the relationship between the corneal biomechanical parameters and the anterior segment parameters in Caucasian children.

METHODS

This study included 293 eyes from 293 healthy children aged between 6 and 17 years. Corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated with the Ocular Response Analyzer, axial length (AL) with IOLMaster and the anterior segment with Pentacam. Anterior segment parameters obtained were the following: central corneal thickness (CCT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and mean anterior and posterior keratometry. Two multiple linear regression models were constructed to assess the association between CH and CRF with anterior segment parameters. A value of p < 0.05 was taken as the criterion for statistical significance in all analyses.

RESULTS

The mean CH and CRF were 12.12 ± 1.71 and 12.30 ± 1.89 mmHg, respectively. Multiple linear regression revealed that CH and CRF were associated negatively with AL in both models, and positively with CCT and CV in the first and second model, respectively. Meanwhile ACD, ACV or mean keratometry did not correlated with CH and CRF. Moreover, when CCT was in the model, it explained more variability for both CH (22.1%) and CRF (30.9%) than when CV was included (16.2% for CH and 16.5% for CRF).

CONCLUSIONS

CH and CRF were correlated positively with CCT and CV, and negatively with AL in healthy Caucasian children. Moreover, corneal parameters were the most contributory variables to CH and CRF changes.

Correlation between elastic energy stored in an eye and visual field progression in glaucoma

PURPOSE

To investigate whether the elastic energy stored in an eyeball at highest concavity (highest concavity energy; HCE), calculated with Corivs ST (CST, OCULUS), correlates with glaucomatous visual field (VF) progression.

METHODS

108 eyes from 70 primary open angle-glaucoma patients were studied. The HCE was calculated using CST parameters. For each eye, the mean total deviation (mTD) of the 52 test points in the 24-2 Humphrey Field Analyzer test pattern was calculated and the mTD progression rate was determined from eight reliable VFs. Eyes were subdivided into: subgroups with low- or high-whole eye motion maximal length (WEM-d) and subgroups with short- or long-time taken to reach WEM-d (WEM-t), as measured with CST. The associations between mTD progression rate and HCE and other ocular/systemic parameters including age, Goldmann applanation tonometry based-intraocular pressure [GAT-IOP], and corneal hysteresis [CH] from the Ocular Response Analyzer (ORA®, Reichert) were investigated using the linear mixed model. The optimal model to describe mTD progression rate was selected from all possible combinations according to the second order bias corrected Akaike Information Criterion index.

RESULTS

Optimal models to describe mTD progression rate included: CH in the model for all eyes, age and HCE in the model for the WEM-d low group, HCE in the model for the WEM-t short group, mean GAT-IOP in the model for the WEM-d high group, and age in the model for the WEM-t long-group.

CONCLUSIONS

HCE was associated with glaucomatous VF progression in eyes with minimal whole eye motion (low WEM-d and WEM-t subgroups).

Assessment of corneal hysteresis measured by the ocular response analyzer as a screening tool in patients with glaucoma

Background

Corneal hysteresis (CH) is used to determine the level of risk of patients developing glaucoma, categorized as suspect, mild, moderate and severe.

Methods

This is a retrospective review of 126 consecutive eyes presenting, for the first time, at a glaucoma subspecialty clinic. All eyes at initial examination underwent measurement of CH and intraocular pressure using the Goldmann applanation tonometry (IOPgat). Eyes were classified as CH<10 (n=51) or CH≥10 (n=75) and categorized into glaucoma suspect, mild, moderate, or severe glaucoma based on 24−2 Humphrey visual field testing. Additional data included number of topical glaucoma medications.

Results

Of the eyes classified as a CH<10, 45.5% had moderate or severe glaucoma, and 11.8% of eyes with a CH≥10 had moderate or severe glaucoma. In the CH≥10 group, the mean IOPgat was 19.5 mmHg ± 4.72 mmHg (P<0.01) on 1 ± 1.26 (P<0.01) medications in the moderate/severe glaucoma group and 20.13 mmHg ± 4.95 mmHg (P<0.01) on 0.60 ± 0.95 (P<0.01) medications in the glaucoma suspect/mild glaucoma group. In the CH<10 group, mean IOPgat was 20.47 mmHg ± 7.56 mmHg (P<0.01) on 1.79 ± 1.17 (P<0.01) medications in the moderate/severe glaucoma group. Mean IOPgat was 17.54 mmHg ± 5.48 mmHg (P<0.01) on 0.63 ± 0.83 (P<0.01) medications in the glaucoma suspect/mild glaucoma group.

Conclusion

Moderate to severe glaucoma is 2.9 (P<0.01) times more likely to occur in eyes that measure a CH<10 compared to eyes that measure a CH≥10. Although not statistically significant, suspect or mild glaucoma is more common in eyes that measure a CH≥10. Eyes in the CH<10 moderate/severe glaucoma group had statistically significant higher IOPgat (P<0.01) compared to the CH<10 suspect/mild glaucoma group. Measuring CH at initial presentation can help predict the severity of glaucoma.

Risk factors for early onset elevated intraocular pressure after pterygium surgery

Purpose

In this study, we aimed to identify the risk factors for early postoperative elevation of intraocular pressure (IOP) after pterygium surgery.

Patients and methods

All patients in this retrospective cohort study were evaluated for inclusion from a single tertiary care center at Boston Medical Center. Their pre- and postoperative IOP measurements (day 1, week 1, month 1, month 3, and when clinically necessary) were compared. Patients with postoperative IOP measurement of >22 mmHg or with an increase in IOP by ≥10 mmHg compared with the preoperative measurement value were grouped as “Ocular Hypertension” group; otherwise, patients were grouped in the “No Ocular Hypertension” group. Age, sex, race, baseline IOP, cup-to-disc (C/D) ratio, history of glaucoma, and frequency of use of postoperative steroid drops in all patients were compared. Chi square test was performed to compare the categorical variables, whereas Student’s t-test was performed to compare continuous variables. We performed a multivariate logistic regression analysis of categorical data with a significance level of p < 0.05.

Results

In total, 240 patient charts were reviewed for inclusion in this study. Twenty-six patients required pterygium surgery on both eyes; for these patients, the eye with higher IOP was analyzed. Two patients were discontinued from this study because of elevated IOP in the contralateral, nonsurgical eye. Fortyeight out of 212 eyes (22.64%) developed postsurgical elevation of IOP within the first 3 months of operation. No significant differences were found between age, sex, baseline IOP, C/D ratio, history of glaucoma diagnoses, and frequency of use of postoperative steroid drops. However, Hispanic/Latino race (p = 0.036) and lack of application of steroid ointment (p = 0.001) were found to be the significant risk factors for the development of “Ocular Hypertension” in multivariate analysis.

Conclusion

Early elevation of IOP is a risk of pterygium surgery. One nonmodifiable risk factor, Hispanic/Latino race, and one modifiable risk factor, lack of application of steroid ointments, were identified as potential causes of early postoperative IOP elevation.

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.

Corneal Stiffness and Its Relationship With Other Corneal Biomechanical and Nonbiomechanical Parameters in Myopic Eyes of Chinese Patients

PURPOSE

To investigate corneal stiffness and analyze its possible influence on other corneal biomechanical and nonbiomechanical parameters in myopic eyes of Chinese patients.

METHODS

A total of 387 healthy (right) myopic eyes were included in this study. Corneal visualization Scheimpflug technology was used to measure the corneal stiffness parameter at the first applanation (SP-A1), deformation amplitude ratio at 1.0 and at 2.0 mm, biomechanically corrected intraocular pressure (bIOP), and corneal deformation parameters during the first applanation (A1: A1-time, A1-length, and A1-velocity), second applanation (A2; A2-time, A2-length, and A2-velocity), and highest concavity (HC; HC-time, HC-radius, HC deformation amplitude, and HC peak distance). The Pentacam was used to evaluate central corneal thickness, mean corneal curvature (Km), anterior corneal central elevation, and corneal asphericity (Q value) of the anterior cornea.

RESULTS

The mean SP-A1 and bIOP values were 90.46 ± 15.39 mm Hg/mm and 13.5 ± 1.85 mm Hg, respectively. The SP-A1 increased with age (β = 0.41 [95% CI, 0.28%-0.54%]; P < 0.0001). Corneal stiffness was positively correlated with central corneal thickness, uncorrected intraocular pressure, and bIOP and was also significantly correlated with all corneal deformation parameters (P < 0.05), except A1-length, HC-time, and HC peak distance. Corneal stiffness was negatively correlated with central corneal elevation of the anterior surface (r = -0.124, P = 0.014) and mean corneal curvature (r = -0.114, P = 0.025) and positively correlated with the Q value of the anterior surface (r = 0.109, P = 0.032).

CONCLUSIONS

Corneal stiffness increased with age. Stronger corneal stiffness may be related to flattening of the cornea and higher intraocular pressure.