Search

In this study, we investigated the integration of an NdFeB N35 permanent magnet into an electromagnetic chuck to maintain its magnetic force continuously. By energizing or deenergizing the coil wrapped around the chuck, the surface magnetic force was increased or decreased, achieving either stronger adhesion or easy detachment of the attached object, respectively. ANSYS Maxwell software was utilized to simulate the initial model, the results of which were then compared with physical measurements. Keeping the external dimensions unchanged, the yoke's dimensions were used as the parameters to analyze the effect of changes in dimensions at different positions on the electromagnetic chuck's surface adhesion force. Differences between simulated and measured results for the initial model after energizing the electromagnetic chuck were within 6%. Among the simulations with different parameters, changes in the thickness of the outer frame base and inner diameter did not significantly affect the magnetic flux on the surface of the electromagnetic chuck. Therefore, these results were not shown in this study. Alterations in the yoke's dimensions affected the relative position and size of the coil or created new magnetic flux paths. A distance of less than 1 mm between the coil and the chuck surface significantly affected the surface magnetic flux density. [ABSTRACT FROM AUTHOR]

In this study, we conducted stress and strain analyses on the eyeball under pressure using the finite element simulation software Ansys. The eyeball model was constructed using SolidWorks, and additionally, it simulates a contact-type tonometer, applying pressure to the eyeball through probe force variations and calculating the pressure changes inside the eyeball. Initially, the cornea, sclera, ciliary body, suspensory ligaments, aqueous humor, and vitreous humor were combined using SolidWorks. Subsequently, the model was imported into Ansys for meshing, boundary setting, and simulation calculation. Finally, the analysis results were extracted using the Ansys postprocessor and the simulated data were validated against actual measurement data to ensure accuracy. Material properties necessary for the eyeball under pressure analyses were configured, with the Mooney-Rivlin hyperelastic material being selected. During compression, the cornea and sclera primarily absorbed the concentrated load after compression. Pressure was applied using a probe to observe variations in stress and strain concerning the applied force and intraocular pressure. Three probe materials (rubber, titanium alloy, and glass) were chosen for comparative simulation analyses. [ABSTRACT FROM AUTHOR]

This study presents a finite element analysis to model ocular biomechanics and the interactions between the human eye and contact lenses in the closed-eye condition. The closed-eye state, where the eyelids are fully shut, presents challenges for experimental measurements due to the invasive nature of accessing and analysing the contact lens and corneal interface, making simulation tools valuable for accurate characterisation. The primary objective of this study was to examine how CLs fold and twist and their impact on the cornea when the eye is closed. The secondary aim of this study was to assess how crucial contact lens parameters (Young's modulus, base curve, and diameter) influence corneal stress distribution and the overall fit of the lens on the eye. The findings show that increasing Young's modulus significantly reduces corneal stress and promotes uniform stress distribution, making it the most influential factor for wearer comfort and safety. While base curve and diameter variations primarily affect contact area, their impact on stress distribution is minimal. This research provides insights for improving contact lens design and enhancing safety for contact lens wearers. [ABSTRACT FROM AUTHOR]

This study investigated the effect of intraocular pressure (IOP) reduction on pulsatile displacement within the optic nerve head (ONH) in primary open-angle glaucoma (POAG) patients with and without axial myopia. Forty-one POAG patients (19 without myopia, 9 with axial myopia and 13 glaucoma with no intervention) participated. Swept-source optical coherence tomography (OCT) videos of the ONH were obtained before and after IOP-lowering treatment (medical or surgical) achieving a minimum IOP drop of 3 mmHg. A demons registration-based algorithm measured local pulsatile displacement maps within the ONH. Results demonstrated a significant 14% decrease in pulsatile tissue displacement in the non-myopic glaucoma cohort after intervention (p = 0.03). However, glaucoma patients with axial myopia exhibited no statistically significant change. There were no significant changes in the pulsatile ONH deformation in the control group. These findings suggest a potential link between IOP reduction and reduced pulsatile displacement within the ONH in POAG patients without myopia, offering new insights into the disease's pathophysiology and warranting further investigation into underlying mechanisms and clinical implications. [ABSTRACT FROM AUTHOR]

This study presents a finite element analysis to model ocular biomechanics and the interactions between the human eye and contact lenses in the closed-eye condition. The closed-eye state, where the eyelids are fully shut, presents challenges for experimental measurements due to the invasive nature of accessing and analysing the contact lens and corneal interface, making simulation tools valuable for accurate characterisation. The primary objective of this study was to examine how CLs fold and twist and their impact on the cornea when the eye is closed. The secondary aim of this study was to assess how crucial contact lens parameters (Young’s modulus, base curve, and diameter) influence corneal stress distribution and the overall fit of the lens on the eye. The findings show that increasing Young’s modulus significantly reduces corneal stress and promotes uniform stress distribution, making it the most influential factor for wearer comfort and safety. While base curve and diameter variations primarily affect contact area, their impact on stress distribution is minimal. This research provides insights for improving contact lens design and enhancing safety for contact lens wearers.

Presbyopia is an age-related ocular disorder where accommodative ability declines so that an individual's focusing range is insufficient to provide visual clarity for near and distance vision tasks without corrective measures. With age, the eye exhibits changes in biomechanical properties of many components involved in accommodation, including the lens, sclera, and ciliary muscle. Changes occur at different rates, affecting accommodative biomechanics differently, but individual contributions to presbyopia are unknown. We used a finite element model (FEM) of the accommodative mechanism to simulate age-related changes in lens stiffness, scleral stiffness, and ciliary contraction to predict differences in accommodative function. The FEM predicts how ciliary muscle action leads to lens displacement by initializing a tensioned unaccommodated lens (Phase 0) then simulating ciliary muscle contraction in accommodation (Phase 1). Model inputs were calibrated to replicate experimentally measured lens and ciliary muscle in 30-year-old eyes. Predictions of accommodative lens deformation were verified with additional imaging studies. Model variations were created with altered lens component stiffnesses, scleral stiffness, or ciliary muscle section activations, representing fifteen-year incremental age-related changes. Model variations predict significant changes in accommodative function with age-related biomechanical property changes. Lens changes only significantly altered lens thickening with advanced age (46% decrease at 75 years old) while sclera changes produced progressive dysfunction with increasing age (23%, 36%, 49% decrease at 45, 60, and 75 years old). Ciliary muscle changes effected lens position modulation. Model predictions identified potential mechanisms of presbyopia that likely work in combination to reduce accommodative function and could indicate effectiveness of treatment strategies and their dependency on patient age or relative ocular mechanical properties. [ABSTRACT FROM AUTHOR]

To assess differences between corneal biomechanical properties in patients with non-infectious uveitis and healthy subjects using CorVis. 77 patients with non-infectious uveitis and 47 control subjects were recruited. Biomechanical parameters were measured: deformation amplitude (DA), A-1 length and A-2 length (L1, L2), A-1 velocity and A-2 velocity (V1, V2), peak distance (PD) and HC radius (highest concavity radius). AUC ROC and correlation between clinical variables and biomechanical properties were determined. Lower HC Radius and IOPb and higher DA and V1 was found in uveitis group. Statistical differences between cases using systemic medications and those with topical treatment were found in L1. Differences were showed between those cases with active and inactive uveitis in PD, DA, V2 and L2. The biomechanical parameter with the best discriminatory capacity of uveitis disease was HC Radius. Differences in corneal biomechanical properties between non-infectious uveitis and healthy eyes were found. [ABSTRACT FROM AUTHOR]

Over the last two decades, there has been growing interest in assessing corneal biomechanics in different diseases, such as keratoconus, glaucoma, and corneal disorders. Given the interaction and structural continuity between the cornea and sclera, evaluating corneal biomechanics may give us further insights into the pathogenesis, diagnosis, progression, and management of glaucoma. Therefore, some authorities have recommended baseline evaluations of corneal biomechanics in all glaucoma and glaucoma suspects patients. Currently, two devices (Ocular Response Analyzer and Corneal Visualization Schiempflug Technology) are commercially available for evaluating corneal biomechanics; however, each device reports different parameters, and there is a weak to moderate agreement between the reported parameters. Studies are further limited by the inclusion of glaucoma subjects taking topical prostaglandin analogues, which may alter corneal biomechanics and contribute to contradicting results, lack of proper stratification of patients, and misinterpretation of the results based on factors that are confounded by intraocular pressure changes. This review aims to summarize the recent evidence on corneal biomechanics in glaucoma patients and insights for future studies to address the current limitations of the literature studying corneal biomechanics. [ABSTRACT FROM AUTHOR]

This study investigated the effect of intraocular pressure (IOP) reduction on pulsatile displacement within the optic nerve head (ONH) in primary open-angle glaucoma (POAG) patients with and without axial myopia. Forty-one POAG patients (19 without myopia, 9 with axial myopia and 13 glaucoma with no intervention) participated. Swept-source optical coherence tomography (OCT) videos of the ONH were obtained before and after IOP-lowering treatment (medical or surgical) achieving a minimum IOP drop of 3 mmHg. A demons registration-based algorithm measured local pulsatile displacement maps within the ONH. Results demonstrated a significant 14% decrease in pulsatile tissue displacement in the non-myopic glaucoma cohort after intervention (p = 0.03). However, glaucoma patients with axial myopia exhibited no statistically significant change. There were no significant changes in the pulsatile ONH deformation in the control group. These findings suggest a potential link between IOP reduction and reduced pulsatile displacement within the ONH in POAG patients without myopia, offering new insights into the disease’s pathophysiology and warranting further investigation into underlying mechanisms and clinical implications.

Introduction: The air puff test is a contactless tonometry test used to measure the intraocular pressure and the cornea’s biomechanical properties. Limitations that most challenge the accuracy of the estimation of the corneal material and the intraocular pressure are the strong intercorrelation between the intraocular pressure and the corneal parameters, either the material properties that can change from one person to another because of age or the geometry parameters like central corneal thickness. This influence produces inaccuracies in the corneal deformation parameters while extracting the IOP parametric equation, which can be reduced through the consideration of the patient-specific air puff pressure distribution taking into account the changes in corneal parameters. This air puff pressure loading distribution can be determined precisely from the fluid-structure interaction (FSI) coupling between the air puff and the eye model. However, the computational fluid dynamics simulation of the air puff in the coupling algorithm is a time-consuming model that is impractical to use in clinical practice and large parametric studies.Methods: By using a supervised machine learning algorithm, we predict the time-dependent air puff pressure distribution for different corneal parameters via a parametric study of the corneal deformations and the gradient boosting algorithm.Results: The results confirmed that the algorithm gives the time-dependent air puff pressure distribution with an MAE of 0.0258, an RMSE of 0.0673, and an execution time of 93 s, which is then applied to the finite element model of the eye generating the corresponding corneal deformations taking into account the FSI influence. Using corneal deformations, the response parameters can be extracted and used to produce more accurate algorithms of the intraocular pressure and corneal material stress-strain index (SSI).Discussion: Estimating the distribution of air pressure on the cornea is essential to increase the accuracy of intraocular pressure (IOP) measurements, which serve as valuable indicator of corneal disease. We find that the air puff pressure loading is largely influenced by complex changes in corneal parameters unique to each patient case. With our innovative algorithm, we can preserve the same accuracy developed by the CFD-based FSI model, while reducing the computational time from approximately 101000 s (28 h) to 720 s (12 min), which is about 99.2% reduction in time. This huge improvement in computational cost will lead to significant improvement in the parametric equations for IOP and the Stress-Strain Index (SSI).

In this work, an attempt has been made to analyze the influence of pathological changes in eye globe dimensions towards the mechanical responses of optic nerve head tissues during eye adductions. For this study, a 3D baseline model geometry of posterior ocular tissues has been constructed. The eye globe diameters of the model are modified to mimic the changes in ocular globe morphology in control, glaucoma, myopia and glaucoma with myopia conditions. Adductions are simulated for each modified model as the rotation of the globe from 1o to 10o in steps of 1o. von Mises strain in lamina cribrosa (LC) and posterior displacement of LC are estimated. Results show that strains developed in LC and its posterior displacement are higher in diseased eyes compared to healthy eyes. It appears that eyes with higher axial length and globe anisotropy are more susceptible to optic nerve head damage. This study might be extended to assess the progression of glaucomatous optic neuropathy.

To review the current published literature on the utility of corneal hysteresis (CH) to assist the clinician in the diagnosis of glaucoma or in the assessment of risk for disease progression in existing glaucoma patients. Searches of the peer-reviewed literature in the PubMed database were performed through July 2022. The abstracts of 423 identified articles were examined to exclude reviews and non-English articles. After inclusion and exclusion criteria were applied, 19 articles were selected, and the panel methodologist rated them for level of evidence. Eight articles were rated level I, and 5 articles were rated level II. The 6 articles rated level III were excluded. Corneal hysteresis is lower in patients with primary open-angle glaucoma, primary angle-closure glaucoma, pseudoexfoliative glaucoma, and pseudoexfoliation syndrome compared with normal subjects. Interpretation of low CH in patients with high intraocular pressure (IOP) or on topical hypotensive medications is complicated by the influence of these parameters on CH measurements. However, CH is also lower in treatment-naïve, normal-tension glaucoma patients compared with normal subjects who have a similar IOP. In addition, lower CH is associated with an increased risk of progression of glaucoma based on visual fields or structural markers in open-angle glaucoma patients, including those with apparently well-controlled IOP. Corneal hysteresis is lower in glaucoma patients compared with normal subjects, and lower CH is associated with an increased risk of disease progression. However, a causal relationship remains to be demonstrated. Nevertheless, measurement of CH complements current structural and functional assessments in determining disease risk in glaucoma suspects and patients. Proprietary or commercial disclosure may be found after the references. [ABSTRACT FROM AUTHOR]

Abstract Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment.

Purpose: Ocular biomechanics is an assessment of the response of the structures of the eye to forces that may lead to disease development and progression, or influence the response to surgical intervention. The goals of this review are (1) to introduce basic biomechanical principles and terminology, (2) to provide perspective on the progress made in the clinical study and assessment of ocular biomechanics, and (3) to highlight critical studies conducted in keratoconus, laser refractive surgery, and glaucoma in order to aid interpretation of biomechanical parameters in the laboratory and in the clinic. Methods: A literature review was first conducted of basic biomechanical studies related to ocular tissue. The subsequent review of ocular biomechanical studies was limited to those focusing on keratoconus, laser refractive surgery, or glaucoma using the only two commercially available devices that allow rapid assessment of biomechanical response in the clinic. Results: Foundational studies on ocular biomechanics used a combination of computer modeling and destructive forces on ex-vivo tissues. The knowledge gained from these studies could not be directly translated to clinical research and practice until the introduction of non-contact tonometers that quantified the deformation response of the cornea to an air puff, which represents a non-destructive, clinically appropriate load. The corneal response includes a contribution from the sclera which may limit corneal deformation. Two commercial devices are available, the Ocular Response Analyzer which produces viscoelastic parameters with a customized load for each eye, and the Corvis ST which produces elastic parameters with a consistent load for every eye. Neither device produces the classic biomechanical properties reported in basic studies, but rather biomechanical deformation response parameters which require careful interpretation. Conclusions: Research using clinical tools has enriched our understanding of how ocular disease alters ocular biomechanics, as well as how ocular biomechanics may influence the pathophysiology of ocular disease and response to surgical intervention. [ABSTRACT FROM AUTHOR]

Purpose: To prospectively review the importance of biomechanical assessment in the screening, diagnosis, prognosis, individualized planning, and clinical follow-up for ectatic corneal diseases. Methods: We demonstrate two commercially available devices to assess the corneal biomechanics in vivo, the Ocular Response Analyzer (ORA, Reichester, NY, USA) and the Corvis ST (Oculus, Wetzlar, Germany). Novel devices have been demonstrated to provide in vivo biomechanical measurements, including Brillouin optical microscopy and OCT elastography. Conclusion: The integration of biomechanical data and other data from multimodal refractive imaging using artificial intelligence demonstrated the ability to enhance accuracy in diagnosing ectatic corneal diseases. [ABSTRACT FROM AUTHOR]

To study the associations between optic nerve head (ONH) strains under intraocular pressure (IOP) elevation with retinal sensitivity in patients with glaucoma. Clinic-based cross-sectional study. Two hundred twenty-nine patients with primary open-angle glaucoma (subdivided into 115 patients with high-tension glaucoma [HTG] and 114 patients with normal-tension glaucoma [NTG]). For 1 eye of each patient, we imaged the ONH using spectral-domain OCT under the following conditions: (1) primary gaze and (2) primary gaze with acute IOP elevation (to approximately 35 mmHg) achieved through ophthalmodynamometry. A 3-dimensional strain-mapping algorithm was applied to quantify IOP-induced ONH tissue strain (i.e., deformation) in each ONH. Strains in the prelaminar tissue (PLT), the retina, the choroid, the sclera, and the lamina cribrosa (LC) were associated (using linear regression) with measures of retinal sensitivity from the 24-2 Humphrey visual field test (Carl Zeiss Meditec). This was performed globally, then locally according to a previously published regionalization scheme. Associations between ONH strains and values of retinal sensitivity from visual field testing. For patients with HTG, we found (1) significant negative linear associations between ONH strains and retinal sensitivity (P < 0.001; on average, a 1% increase in ONH strains corresponded to a decrease in retinal sensitivity of 1.1 decibels [dB]), (2) that high-strain regions colocalized with anatomically mapped regions of high visual field loss, and (3) that the strongest negative associations were observed in the superior region and in the PLT. In contrast, for patients with NTG, no significant associations between strains and retinal sensitivity were observed except in the superotemporal region of the LC. We found significant negative associations between IOP-induced ONH strains and retinal sensitivity in a relatively large glaucoma cohort. Specifically, patients with HTG who experienced higher ONH strains were more likely to exhibit lower retinal sensitivities. Interestingly, this trend in general was less pronounced in patients with NTG, which could suggest a distinct pathophysiologic relationship between the two glaucoma subtypes. [ABSTRACT FROM AUTHOR]

Over the last two decades, there has been growing interest in assessing corneal biomechanics in different diseases, such as keratoconus, glaucoma, and corneal disorders. Given the interaction and structural continuity between the cornea and sclera, evaluating corneal biomechanics may give us further insights into the pathogenesis, diagnosis, progression, and management of glaucoma. Therefore, some authorities have recommended baseline evaluations of corneal biomechanics in all glaucoma and glaucoma suspects patients. Currently, two devices (Ocular Response Analyzer and Corneal Visualization Schiempflug Technology) are commercially available for evaluating corneal biomechanics; however, each device reports different parameters, and there is a weak to moderate agreement between the reported parameters. Studies are further limited by the inclusion of glaucoma subjects taking topical prostaglandin analogues, which may alter corneal biomechanics and contribute to contradicting results, lack of proper stratification of patients, and misinterpretation of the results based on factors that are confounded by intraocular pressure changes. This review aims to summarize the recent evidence on corneal biomechanics in glaucoma patients and insights for future studies to address the current limitations of the literature studying corneal biomechanics.

Objective: To develop a noninvasive technique to quantitatively assess the pulsatile deformation due to cardiac contractions of the optic nerve head (ONH). Design: Evaluation of a diagnostic test or technology. Participants: Healthy subjects with no history of refractive surgery, divided into 2 cohorts on the basis of their axial length (AL). Methods: We present a noninvasive technique to quantitatively assess the pulsatile deformation of the ONH tissue by combining high-frequency OCT imaging and widely available image processing algorithms. We performed a thorough validation of the approach, numerically and experimentally, evaluating the sensitivity of the method to artificially induced deformation and its robustness to different noise levels. We performed deformation measurements in cohorts of healthy (n = 9) and myopic (n = 5) subjects in different physiological strain conditions by calculating the amplitude of tissue displacement in both the primary position and abduction. The head rotation was measured using a goniometer. During imaging in abduction, the head was rotated 40° ± 3°, and subjects were instructed to direct their gaze toward the OCT visual target. Main Outcome Measures: Pulsatile tissue displacement maps. Results: The robustness of the method was assessed using artificial deformations and increasing noise levels. The results show acceptable absolute errors before the noise simulations grossly exaggerate image degradation. For the group of subjects with AL of < 25 mm (n = 9), the median pulsatile displacement of the ONH was 7.8 ± 1.3 μm in the primary position and 8.9 ± 1.2 μm in abduction. The Wilcoxon test showed a significant difference (P ≤ 0.005) between the 2 paired measures. Reproducibility was tested in 2 different sessions in 5 different subjects with the same intraocular pressure, and an intraclass correlation coefficient of 0.99 was obtained (P < 0.005). Conclusions: The computational pipeline demonstrated good reproducibility and had the capacity to accurately map the pulsatile deformation of the optic nerve. In a clinical setting, we detected physiological changes in normal subjects supporting its translation potential as a novel biomarker for the diagnosis and progression of optic nerve diseases.

Kulawan Rojananuangnit Glaucoma Unit, Ophthalmology Department, Mettapracharak (Wat Rai Khing) Hospital, Nakhon Pathom, ThailandCorrespondence: Kulawan Rojananuangnit Email kulawan@me.comPurpose: To collect the normal value data of corneal hysteresis in Thais and study the variation of corneal hysteresis in glaucomatous eyes.Methods: Retrospective cross-sectional study of corneal hysteresis (CH) in healthy non-glaucomatous and glaucomatous eyes. Demographic data, type and staging of glaucoma, Goldmann applanation tonometry (GAT) and ocular response analyzer parameters; CH, corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOPg) were collected.Results: Data from one eye of 465 normal participants were included for the normal value data of CH. Mean CH, IOPcc and IOPg were 10.18 ± 1.48, 15.01 ± 3.04 and 14.16 ± 3.06 mmHg, respectively. Average age was 57.21 ± 14.4 years. CH at the fifth percentile was 8.0 mmHg. Women had significantly higher CH than men (10.29 ± 1.46 vs 9.90 ± 1.49 mmHg, p=0.009). Moderate negative correlation was found between age and CH, r = − 0.338, p< 0.001. There were 695 glaucomatous eyes from 429 patients including primary-open angle glaucoma (POAG), primary close-angle glaucoma (PACG), normal tension glaucoma (NTG) and ocular hypertension (OHT). CH in each glaucoma type and severity stage (early, moderate and severe) were as follows: POAG: 8.74 ± 1.52 mmHg (9.22 ± 1.47, 8.74 ± 1.23 and 7.92 ± 1.40 mmHg, p< 0.001), PACG: 9.09 ± 1.72 mmHg (9.85 ± 1.45, 9.04 ± 1.68 and 8.45 ± 1.74 mmHg, p= 0.004), NTG: 9.55 ± 1.67 mmHg (9.47 ± 1.38, 9.75 ± 2.42 and 9.77 ± 1.34 mmHg, p 0.525) and OHT: 10.10 ± 1.40 mmHg.Conclusion: Compared with normal value data of corneal hysteresis, CH in glaucomatous eyes was lower. The more advanced glaucoma stage was associated with lower CH. Arising from normal value data, a low percentile of CH could be applied as the deviation value from normal and this dynamic property of CH could represent a glaucoma predictor in an effort to improve glaucoma care.Keywords: corneal hysteresis, CH, corneal-compensated intraocular pressure, IOPcc, Goldmann-correlated intraocular pressure, IOPg, glaucoma, normative database, ocular biomechanics

Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment. [ABSTRACT FROM AUTHOR]

Orthokeratology has been widely used to control myopia, but the mechanism is still unknown. To further investigate the underlying mechanism of corneal reshaping using orthokeratology lenses via the finite element method, numerical models with different corneal curvatures, corneal thicknesses, and myopia reduction degrees had been developed and validated to simulate the corneal response and quantify the changes in maximum stress in the central and peripheral corneal areas during orthokeratology. The influence of the factors on corneal response had been analyzed by using median quantile regression. A partial eta squared value in analysis of variance models was established to compare the effect size of these factors. The results showed central and peripheral corneal stress responses changed significantly with increased myopia reduction, corneal curvature, and corneal thickness. The target myopia reduction had the greatest effect on the central corneal stress value (partial eta square = 0.9382), followed by corneal curvature (partial eta square = 0.5650) and corneal thickness (partial eta square = 0.1975). The corneal curvature had the greatest effect on the peripheral corneal stress value (partial eta square = 0.5220), followed by myopia reduction (partial eta square = 0.2375) and corneal thickness (partial eta square = 0.1972). In summary, the biomechanical response of the cornea varies significantly with the change in corneal conditions and lens designs. Therefore, the orthokeratology lens design and the lens fitting process should be taken into consideration in clinical practice, especially for patients with high myopia and steep corneas.

Fractal dimension (FD) together with advances in imaging technologies has provided an increasing application of digital images to interpret biological phenomena. In ophthalmology, topography-based images are increasingly used in common practices of clinical settings. They provide detailed information about corneal surfaces. Few-micron alterations of the corneal geometry to the elevation and curvature cause a highly multifocal surface, change the corneal optical power up to several diopters, and therefore adversely affect the individual’s vision. Keratoconus (KCN) is a corneal disease characterized by a local alteration of the corneal anatomical and mechanical features. The formation of cone-shaped regions accompanied by thinning and weakening of the cornea are the major manifestations of KCN. The implantation of tiny arc-like polymeric sections, known as intracorneal implants, is considered to be effective in restoring the corneal curvature. This study investigated the FD nature of healthy corneas (n = 7) and compared it to the corresponding values before and after intracorneal implant surgery in KCN patients (n = 7). The generalized Hurst exponent, Higuchi, and Katz FDs were computed for topography-based parameters of corneal surfaces: front elevation (ELE-front), back elevation (ELE-back), and corneal curvature (CURV). The Katz FD showed better discriminating ability for the diseased group. It could reveal a significant difference between the healthy corneas and both pre- and post-implantation topographies (p < 0.001). Moreover, the Katz dimension varied between the topographic features of KCN patients before and after the treatment (p < 0.036). We propose to describe the curvature feature of corneal topography as a “strange attractor” with a self-similar (i.e., fractal) structure according to the Katz algorithm.

Purpose: To assess ocular rigidity using dynamic optical coherence tomography (OCT) videos in glaucomatous and healthy subjects, and to evaluate how ocular rigidity correlates with biomechanical and morphological characteristics of the human eye.Methods: Ocular rigidity was calculated using Friedenwald's empirical equation which estimates the change in intraocular pressure (IOP) produced by volumetric changes of the eye due to choroidal pulsations with each heartbeat. High-speed OCT video was utilized to non-invasively measure changes in choroidal volume through time-series analysis. A control-case study design was based on 23 healthy controls and 6 glaucoma cases. Multiple diagnostic modalities were performed during the same visit including Spectralis OCT for nerve head video, Pascal Dynamic Contour Tonometry for IOP and ocular pulse amplitude (OPA) measurement, Corvis ST for measuring dynamic biomechanical response, and Pentacam for morphological characterization.Results: Combining glaucoma and healthy cohorts (n = 29), there were negative correlations between ocular rigidity and axial length (Pearson R = −0.53, p = 0.003), and between ocular rigidity and anterior chamber volume (R = −0.64, p = 0.0002). There was a stronger positive correlation of ocular rigidity and scleral stiffness (i.e., stiffness parameter at the highest concavity [SP-HC]) (R = 0.62, p = 0.0005) compared to ocular rigidity and corneal stiffness (i.e., stiffness parameter at the first applanation [SP-A1]) (R = 0.41, p = 0.033). In addition, there was a positive correlation between ocular rigidity and the static pressure-volume ratio (P/V ratio) (R = 0.72, p < 0.0001).Conclusions: Ocular rigidity was non-invasively assessed using OCT video and OPA in a clinic setting. The significant correlation of ocular rigidity with biomechanical parameters, SP-HC and P/V ratio, demonstrated the validity of the ocular rigidity measurement. Ocular rigidity is driven to a greater extent by scleral stiffness than corneal stiffness. These in vivo methods offer an important approach to investigate the role of ocular biomechanics in glaucoma.

The eye's accommodative mechanism changes optical power for near vision. In accommodation, ciliary muscle excursion relieves lens tension, allowing it to return to its more convex shape. Lens deformation alters its refractive properties, but the mechanics of ciliary muscle actions are difficult to intuit due to the complex architecture of the tissues involved. The muscle itself comprises three sections of dissimilarly oriented cells. These cells contract, transmitting forces through the zonule fibers and extralenticular structures. This study aims to create a finite element model (FEM) to predict how the action of the ciliary muscle sections leads to lens displacement. The FEM incorporates initialization of the disaccommodated lens state and ciliary muscle contraction, with three muscle sections capable of independent activation, to drive accommodative movement. Model inputs were calibrated to replicate experimentally measured disaccommodated lens and accommodated ciliary muscle shape changes. Additional imaging studies were used to validate model predictions of accommodative lens deformation. Models were analyzed to quantify mechanical actions of ciliary muscle sections in lens deformation and position modulation. Analyses revealed that ciliary muscle sections act synergistically: the circular section contributes most to increasing lens thickness, while longitudinal and radial sections can oppose this action. Conversely, longitudinal and radial sections act to translate the lens anteriorly with opposition from the circular section. This FEM demonstrates the complex interplay of the three sections of ciliary muscle in deforming and translating the lens during accommodation, providing a useful framework for future investigations of accommodative dysfunction that occurs with age in presbyopia. [ABSTRACT FROM AUTHOR]

• High-speed optical biometry enables assessment of the eye reaction to air-puff stimulus. • The eyes with keratoconus showed higher and longer displacements of the cornea. • No significant differences in extracted parameters between forme fruste keratoconus and normal eyes was revealed. The aim of this study was to characterize corneal dynamic response in normal subjects (NL), patients with forme fruste keratoconus (FFKC) and patients with clinical keratoconus (KC) using air-puff OCT-based optical biometry. This cross-sectional study included 50 normal eyes (NL), 15 forme fruste eyes (FFKC) and 31 eyes with early and moderate keratoconus (KC). Keratometry and pachymetry were performed with MS-39 (CSO, Italy). The dynamic response of the corneal apex to air-puff stimulus was imaged with an optical biometer combined with the air-puff system allowing correction for whole eye retraction. The amplitude and duration of corneal displacement, the maximum velocity of the cornea during loading and recovery and hysteresis loop area were extracted from the data. The differences between NL, FFKC and KC groups were tested and the correlation between extracted biomechanical parameters and age, intraocular pressure (IOP) or corneal geometry was assessed for each group. Maximum corneal displacement was higher in the KC eyes than in the NL eyes (p < 0.001), corneal response was longer and maximum velocity of corneal apex was higher in KC eyes (p < 0.05). No significant difference in extracted parameters was detected between FFKC and NL eyes. The parameters of corneal biomechanical response depended mostly on IOP and corneal thickness in NL eyes. Weaker correlation patterns were found in KC and FFKC eyes. High-speed optical biometry combined with an air-puff stimulation allows for the evaluation of the corneal biomechanics. Keratoconus affects corneal biomechanics but the parameters measured could not effectively distinguish forme fruste keratoconus from normal eyes. [ABSTRACT FROM AUTHOR]

An intraocular lens (IOL) is a lens implanted in the eye to correct refractive errors after cataract surgery. It plays a crucial role in ocular biomechanics since it is frequently used to replace the natural eye lens. Understanding the mechanical behavior of the eye and its effect on the IOL after implantation is essential to ensure surgical success and long-term stability. In addition, the precise analysis of IOL parameters, such as spherical power, is a critical task. Therefore, the current study aims to propose a non-contact optical method for the accurate measurement of the spherical power of monofocal IOLs. The proposed method is based on sensing the wavefront transmitted from the IOL being tested using a phase gradient-based approach. The approach relies on using an adaptive optical system consisting of a Shack-Hartmann wavefront sensor (SHWFS) and a deformable mirror (DM). The system evaluates the phase gradient and subsequently reconstructs the wavefront transmitted by the tested IOL. The DM is used to compensate for the aberrations induced by the illumination laser beam, the wet cell containing the IOL and all the optical components integrated in the system. Three monofocal IOLs have been tested using two wavelengths: λ G = 531.2 nm and λ R = 634.449 nm. The results reveal that there is a difference between the measurements before and after aberrations compensation, indicating the impact of the existing aberrations on the measurements. Furthermore, the repeatability of the measurements was evaluated to determine the stability of the repeated measures, and the dynamic range of the proposed system was estimated. • An adaptive phase gradient-based metrology system was proposed for precise spherical power measurement of monofocal IOLs. • The aberrations associated with the laser beam, the wet cell, and the lenses in the measurement system were compensated. • Dispersion and Abbe number of the IOLs materials (hydrophobic acrylic) were estimated to evaluate the refractive efficiency. • The proposed system yields repeatable measurements and an extended dynamic range to precisely evaluate a wide range of IOLs. [ABSTRACT FROM AUTHOR]

• Residual attention network (RAN) - is network architecture, which employs convolutional layers, integrates a diverse attention mechanism within its deep structure. • Our study shows that RAN is a suitable tool for distinguishing between optic disc drusen and normal optic discs on the basis of OCT-A B-scans of the optic nerve head. • Deep learning in ocular imaging may be used as a possible solution to screen, diagnose and monitor major eye diseases for patients in primary care and community settings, including ODD. In this study the authors propose a new solution for distinguish healthy cases and those with optic disc drusen (ODD) utilizing Residual Attention Network (RAN). This network architecture, which employs convolutional layers, integrates a diverse attention mechanism within its deep structure. In this study, an unique approach is adopted, involving the iterative division and subsequent recombination of a single image B-scan obtained using OCT-A. Overall, 116 images of ODD obtained using optical coherence tomography - angiography (OCT-A) have been analysed and compared to images of healthy optic discs. A sequence of trials was conducted, considering the random partitioning of data into training, validation, and test elements, with proportions of 60 %, 20 %, and 20 %, respectively. The minimum accuracy exceeded 86 %, while the maximum values were higher than 98 %. The accuracy for analyzing healthy cases and ones with ODD has gained very satisfactory results. Our study shows that RAN is a suitable tool for distinguishing between optic disc drusen and normal optic discs on the basis of OCT-A B-scans of the optic nerve head. Deep learning may be used as a possible solution to screen for patients with ODD. [ABSTRACT FROM AUTHOR]

Glaucoma is a complex group of optic neuropathies that affects both humans and animals. Intraocular pressure (IOP) elevation is a major risk factor that results in the loss of retinal ganglion cells (RGCs) and their axons. Currently, lowering IOP by medical and surgical methods is the only approved treatment for primary glaucoma, but there is no cure, and vision loss often progresses despite therapy. Recent technologic advances provide us with a better understanding of disease mechanisms and risk factors; this will permit earlier diagnosis of glaucoma and initiation of therapy sooner and more effectively. Gene and cell therapies are well suited to target these mechanisms specifically with the potential to achieve a lasting therapeutic effect. Much progress has been made in laboratory settings to develop these novel therapies for the eye. Gene and cell therapies have already been translated into clinical application for some inherited retinal dystrophies and age‐related macular degeneration (AMD). Except for the intravitreal application of ciliary neurotrophic factor (CNTF) by encapsulated cell technology for RGC neuroprotection, there has been no other clinical translation of gene and cell therapies for glaucoma so far. Possible application of gene and cell therapies consists of long‐term IOP control via increased aqueous humor drainage, including inhibition of fibrosis following filtration surgery, RGC neuroprotection and neuroregeneration, modification of ocular biomechanics for improved IOP tolerance, and inhibition of inflammation and neovascularization to prevent the development of some forms of secondary glaucoma. [ABSTRACT FROM AUTHOR]

PurposeThe elevation of intraocular pressure (IOP), a major risk factor in glaucoma, is an important parameter tracked in experimental models of this disease. However, IOP measurement in laboratory rodents is challenging and may not correlate with some key pathological events that occur in the development of glaucoma. The aims of this study were to quantify changes in ocular morphology in DBA/2J mice that develop spontaneous, age-dependent, pigmentary glaucoma and to check the possible correlation of these parameters with IOP.MethodEye morphology was evaluated with MRI in DBA/2J, DBA/2J-Gpnmb+/SjJ, and C57BL/6J female mice ages 3, 6, 9, 12, and 15 months. The animals were anesthetized with isoflurane. A planar receive-only surface coil (inner diameter = 10 mm) was placed over each animal’s left eye and the image was acquired with a 7T small animal-dedicated magnetic resonance tomograph and T2-weighted TurboRARE sequence. Ocular dimensions were manually quantitated using OsiriX software. IOP was measured with rebound tonometry.ResultsIn the control animals, no age-related changes in the ocular morphology were noted. Since 6 months of age, the anterior chamber deepening and elongation of the eyeballs of DBA/2J mice was detectable. We found a significant, positive correlation between IOP and axial length, anterior chamber area, or anterior chamber width in C57BL/6J mice but not in DBA/2J mice. However, after excluding the measurements performed in the oldest DBA/2J mice (i.e. analyzing only the animals ages 3 to 12 months), we demonstrated a significant positive correlation between IOP and anterior chamber width.ConclusionHigh-resolution magnetic resonance imaging of the eye area in mice enables reproducible and consistent measures of key dimensions of the eyeball. We observed age-dependent alterations in the eye morphology of DBA/2J mice that mostly affected the anterior chamber. We also demonstrated a correlation between some of the ocular dimensions and the IOP of C57Bl/6J mice and DBA/2J mice with moderately advanced glaucomatous pathology.

Purpose: This paper presents and clinically validates two algorithms for estimating intraocular pressure (IOP) and corneal material behavior using numerical models that consider the fluid-structure interaction between the cornea and the air-puff used in non-contact tonometry.Methods: A novel multi-physics fluid-structure interaction model of the air-puff test was employed in a parametric numerical study simulating human eyes under air-puff pressure with a wide range of central corneal thickness (CCT = 445–645 μm), curvature (R = 7.4–8.4 mm), material stiffness and IOP (10–25 mmHg). Models were internally loaded with IOP using a fluid cavity, then externally with air-puff loading simulated using a turbulent computational fluid dynamics model. Corneal dynamic response parameters were extracted and used in development of two algorithms for IOP and corneal material behavior; fIOP and fSSI, respectively. The two algorithms were validated against clinical corneal dynamic response parameters for 476 healthy participants. The predictions of IOP and corneal material behavior were tested on how they varied with CCT, R, and age.Results: The present study produced a biomechanically corrected estimation of intraocular pressure (fIOP) and a corneal material stiffness parameter or Stress-Strain Index (fSSI), both of which showed no significant correlation with R (p > 0.05) and CCT (p > 0.05). Further, fIOP had no significant correlation with age (p > 0.05), while fSSI was significantly correlated with age (p = 0.001), which was found earlier to be strongly correlated with material stiffness.Conclusion: The present study introduced two novel algorithms for estimating IOP and biomechanical material behavior of healthy corneas in-vivo. Consideration of the fluid structure interaction between the cornea and the air puff of non-contact tonometry in developing these algorithms led to improvements in performance compared with bIOP and SSI.

Purpose: The elevation of intraocular pressure (IOP), a major risk factor in glaucoma, is an important parameter tracked in experimental models of this disease. However, IOP measurement in laboratory rodents is challenging and may not correlate with some key pathological events that occur in the development of glaucoma. The aims of this study were to quantify changes in ocular morphology in DBA/2J mice that develop spontaneous, age-dependent, pigmentary glaucoma and to check the possible correlation of these parameters with IOP. Method: Eye morphology was evaluated with MRI in DBA/2J, DBA/2J-Gpnmb+/SjJ, and C57BL/6J female mice ages 3, 6, 9, 12, and 15 months. The animals were anesthetized with isoflurane. A planar receive-only surface coil (inner diameter = 10 mm) was placed over each animal's left eye and the image was acquired with a 7T small animal-dedicated magnetic resonance tomograph and T2-weighted TurboRARE sequence. Ocular dimensions were manually quantitated using OsiriX software. IOP was measured with rebound tonometry. Results: In the control animals, no age-related changes in the ocular morphology were noted. Since 6 months of age, the anterior chamber deepening and elongation of the eyeballs of DBA/2J mice was detectable. We found a significant, positive correlation between IOP and axial length, anterior chamber area, or anterior chamber width in C57BL/6J mice but not in DBA/2J mice. However, after excluding the measurements performed in the oldest DBA/2J mice (i.e. analyzing only the animals ages 3 to 12 months), we demonstrated a significant positive correlation between IOP and anterior chamber width. Conclusion: High-resolution magnetic resonance imaging of the eye area in mice enables reproducible and consistent measures of key dimensions of the eyeball. We observed age-dependent alterations in the eye morphology of DBA/2J mice that mostly affected the anterior chamber. We also demonstrated a correlation between some of the ocular dimensions and the IOP of C57Bl/6J mice and DBA/2J mice with moderately advanced glaucomatous pathology. [ABSTRACT FROM AUTHOR]

Due to chronic exposure to hyperglycemia, the ocular biomechanical homeostasis of diabetics is disturbed, which may cause multiple ocular diseases, such as diabetic retinopathy (DR). In retinal optical coherence tomography (OCT) images of patients with DR, hyperreflective dots (HRDs) are spot-shaped areas with high reflectivity and high local contrast. Quantitative analyses of HRDs are the key to make appropriate decisions on diagnosis and treatment. The small scale, similarity to background and interference of other foci bring great challenges to accurate and automatic segmentation of HRDs. To address above challenges, we propose a novel region-level context network (RC-Net), which introduces region-level position attention module (RPAM) and region-level channel attention module (RCAM) for HRDs segmentation. Four RPAMs are embedded behind ordinary convolution blocks to extract rich contextual dependencies, which help to cluster pixels in same class and reveal differences between HRDs and background. To further improve feature representation, a RCAM is embedded into the top of the encoder structure to adaptively utilize the semantic dependencies between different channels. We evaluate the proposed RC-Net on a dataset, which consists of 450 2D OCT B-scans. The mean and standard deviation of dice similarity coefficient (DSC), intersection over union (IoU), recall (R) and precision (P) are 75.29±0.42%, 62.27±0.54%, 78.36±1.79% and 75.34±0.52%, respectively. The experiments show that the proposed RC-Net achieves superior segmentation performance of HRDs segmentation to state-of-the-art methods. • We propose a novel region-level context network (RC-Net) with region level attention mechanism to extract more powerful feature maps. • A region-level position attention module (RPAM) is proposed to learn region-level spatial long-range context dependencies. • A region-level channel attention module (RCAM) is designed to aggregate high-level semantic features in channel dimensions. • Compared with other CNN-based methods, the proposed RC-Net achieves state-of-the-art results. [ABSTRACT FROM AUTHOR]

The vitreous humour plays an important role in shock absorption, i.e. the damping of the mechanical movement, to protect the delicate tissues within the eye. However, this damping is different for movements with different frequencies/velocities. While the collective low-frequency (below 100 Hz) damping behaviour of the vitreous humour associated with the saccadic and lens movements is well-studied, to the best of our knowledge, the high-frequency damping behaviour of the vitreous humour, which represents the response of the microstructural components, is not exhaustively documented. Here, we utilise a non-destructive testing method called Optical Coherence Tomography (OCT) to measure the high-frequency (100–350 Hz, waves able to probe approximately 500 µm distances) biomechanical behaviour of the vitreous humour. We parametrise this behaviour by calculating the shear storage modulus, shear loss modulus and phase angle. We compare these parameters to their low-frequency counterparts obtained with a rheometer, providing a comprehensive mechanical spectrum of the vitreous humour behaviour. The processing method developed in this study and the data collected help better understand the vitreous humour shock absorption properties. Consequently, they could allow a development of better vitreous humour substitutes. The local probing of the high-frequency regime and the non-invasive character of the OCT method provide new qualities in mapping the damping behaviour. [ABSTRACT FROM AUTHOR]

• PS-OCT can detect abnormalities in the blood vessel wall associated with hypertension. • A new metric termed blood vessel birefringence index (BBI) is introduced. • BBI is able to distinguish between hypertensive and normotensive subjects. • PS-OCT-based BBI indicates high sensitivity and specificity when used as a biomarker. Blood vessel walls are made of organized fibrous tissue with intrinsic birefringence. Even in its very early stages, hypertension can change the structure of a blood vessel wall. In this paper, we demonstrated that this structural change associated with hypertension can be quantitatively measured non-invasively in the human retina using polarization-sensitive optical coherence tomography (PS-OCT). Measurements were performed with a relatively low-cost PS-OCT instrument in less than a minute per eye. Organizational loss in vessel wall tissue was quantified in hypertensive patients and compared to data obtained from age-matched healthy subjects. Our PS-OCT measurements showed that the vessel wall tissue in patients with hypertension is thicker, and exhibited lower birefringence, presumably due to a loss of tissue organization. The blood vessel wall birefringence index (BBI) is a newly introduced metric that combines vessel wall birefringence (decreases with hypertension) and thickness (increases with hypertension) into a single numerical value. Its purpose is to easily differentiate between the blood vessel walls of hypertensives and those of healthy subjects. Accurately determining the thickness of the blood vessel wall relies on access to polarization-sensitive data: a linear increase in retardation in the vessel wall with depth and stable retardation values below the vessel wall to determine the lower edge of the vessel wall. Based on receiver operating characteristic (ROC) curves, BBI showed 99 % sensitivity and 100 % specificity when discriminating normotensive (N = 11) and hypertensive (N = 11) subjects. [ABSTRACT FROM AUTHOR]

• The eye lens needs to be loaded with pre-stress to simulate distant vision to near vision. • The anterior and equatorial zonules carry the highest tensions during accommodation. • The anterior zonules have a negative effect during lens far-to-near accommodation. • The equatorial zonules have a positive effect during lens far-to-near accommodation. To explore the synergistic function of the ligaments in eye, the zonular fibres, that mediate change in eye lens shape to allow for focussing over different distances. A set of 3D Finite Element models of the anterior eye together with a custom developed pre-stress modelling approach was proposed to simulate vision for distant objects (the unaccommodated state) to vision for near objects (accommodation). One of the five zonular groups was cut off in sequence creating five models with different zonular arrangements, the contribution of each zonular group was analysed by comparing results of each specific zonular-cut model with those from the all-zonules model in terms of lens shape and zonular tensions. In the all-zonular model, the anterior and equatorial zonules carry the highest tensions. In the anterior zonular-cut model, the equatorial zonular tension increases while the posterior zonular tension decreases, resulting in an increase in the change in Central Optical Power (COP). In the equatorial zonular-cut model, both the anterior and posterior zonular tensions increase, causing a decreasing change in COP. The change in COP decreases only slightly in the other models. For vitreous zonular-cut models, little change was seen in either the zonular tension or the change in COP. The anterior and the equatorial zonular fibres have the major influence on the change in lens optical power, with the anterior zonules having a negative effect and the equatorial zonules contributing a positive effect. The contribution to variations in optical power by the equatorial zonules is much larger than by the posterior zonules. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the in vivo effect of scleral buckle surgery on ocular biomechanics and aqueous humor dynamics., Design: Prospective observational cross-sectional study., Participants: Nine patients with unilateral 360 degree encircling scleral buckles without vitrectomy for rhegmatogenous retinal detachments, between 3 and 39 months postoperative., Methods: All measurements were performed in both eyes of all participants. Intraocular pressure (IOP) was measured in the seated and supine positions using pneumatonometry. Outflow facility was measured using 2-minute weighted pneumatonography. Ocular rigidity coefficient was determined from the Friedenwald equations based on the difference in IOP with and without a weighted tonometer tip. The percentage change in IOP upon transitioning from seated to supine was calculated. Measurements for buckled and nonbuckled eyes were compared using paired Student t test of means., Main Outcome Measures: Sitting and supine IOP and percentage difference between the 2 positions; outflow facility; ocular rigidity coefficient., Results: Seated IOP was similar between buckled and nonbuckled eyes (16.1 ± 2.5 vs. 16.7 ± 2.7 mmHg; P = 0.5) whereas supine IOP was lower in buckled eyes compared with nonbuckled eyes (18.7 ± 2.6 vs. 21.3 ± 2.5 mmHg; P = 0.008). The percentage increase in IOP upon change in body position from seated to supine was greater in nonbuckled eyes (17.4 ± 9.4% vs. 27.6 ± 9.5%; P = 0.005). Ocular rigidity coefficient was lower in buckled (9.9 × 10 -3 ± 1.4 × 10 -3 μL -1 ) vs. nonbuckled eyes (14.4 × 10 -3 ± 3.1 × 10 -3 μL -1 ; P = 0.006). Outflow facility was not significantly different in buckled and nonbuckled eyes., Conclusions: Scleral buckling decreases ocular rigidity but does not affect outflow facility. This change in ocular biomechanics likely results in the attenuated IOP change from seated to supine position. Decreased ocular rigidity may also reduce IOP fluctuations and potentially reduce the risk for glaucoma progression., Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article., (Copyright © 2023 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.)

The vitreous humor is a fragile, transparent hydrogel situated between the lens and the retina, occupying 80% of the eye's volume. Due to its viscoelastic behavior, the vitreous serves as a mechanical damper for the eye, absorbing impacts, and protecting the lens and retina. The vitreous liquefies with age, which compromises its function as a shock absorber and causes complications including retinal detachment, macular holes, and vitreous hemorrhage. Studies on the viscoelastic properties of the vitreous have been limited. Rheological testing of the vitreous has commonly been done on non-primate mammalian species. Human vitreous rheological properties have been previously reported; however, various measurement techniques were used, resulting in data that differed by orders of magnitude. Shear rheometry is commonly used to characterize soft tissues and hydrogels such as the vitreous humor. However, no human vitreous rheological data have been reported using this technique, preventing direct comparison to other published work. Additionally, no age-related changes in the mechanical properties of the human vitreous humor have been reported. Human vitreous samples (n = 39, aged 62 ± 15 years) were tested using a shear rheometer. Small amplitude oscillatory shear and creep experiments were performed. The linear viscoelastic region of the human vitreous was found to be below 1% strain. The solid phase of the old human vitreous was found to be stiffer than the young human vitreous and the porcine vitreous. The stiffness of the human vitreous gel also appeared to be positively correlated with age. Vitreous dehydration due to a decrease in hyaluronic acid concentration with age was proposed to cause the stiffening of the solid phase of the vitreous gel. Vitreous liquefaction, therefore, might be characterized as a simultaneous increase in liquid volume and localized stiffening of the vitreous gel. The phase separation of the vitreous humor with age has been hypothesized as the cause of many vitreous-related complications. This study provides viscoelastic properties and age-related changes of the human vitreous humor, which will aid in the design of biomimetic vitreous substitutes, enhancement in analyzing intravitreal transport of therapeutics, and understanding the pathological conditions of the vitreous humor.

Mechanical forces play an important role in the behavior and development of biological systems and disease at all spatial scales, from cells and their constituents to tissues and organs. Such forces have a profound influence on the health, structural integrity, and normal function of cells and organs. Accurate knowledge of cell and tissue biomechanical properties is essential to map the distribution of forces and mechanical cues in biological systems. Cell and tissue biomechanical properties are also known to be important on their own as indicators of health or disease states. Hence, optical elastography and biomechanics methods can aid in the understanding and clinical diagnosis of a wide variety of diseases. We provide a brief overview and highlight of the Optical Elastography and Tissue Biomechanics VI conference, which took place in San Francisco, February 2 and 3, 2019, as a part of Photonics West symposium. [ABSTRACT FROM AUTHOR]

Purpose: To quantify biomechanical change associated with autoimmune diseases using Corvis ST deformation data. Methods: Cross-sectional, observational, case control study of 76 patients with systemic autoimmune disease and 21 control subjects. All patients underwent detailed ophthalmic examination with Corvis-ST (Oculus Optikgerate Gmbh, Germany) measurements for biomechanical properties of the eye. Corneal deformation and also deformation caused by the extracorneal tissue were recorded. Using a mathematical formula, the three parameters, namely, corneal stiffness (kc), extracorneal tissue stiffness (kg), and extracorneal tissue viscosity (μg), were defined. Results: The biomechanical analysis showed that kc and μg were significantly lower in patients with systemic autoimmune disease with eye manifestations than control group. However statistically, it was significant in rheumatoid arthritis (RA) patients only. Conclusion: The new parameters, namely, kc, kg, and μg, can provide a sensitive marker of the ocular activity of the collagen vascular diseases. [ABSTRACT FROM AUTHOR]

This work presents results from numerical simulations of optic nerve head's (ONH) biomechanical behavior during exposure to elevated intraocular (IOP) and/or intracranial pressure (ICP) for ocular hypertension conditions. At the same time, a range of geometric and material properties of the eye structure and their interrelation with elevated IOP and ICP values are investigated. These simulations are performed on a generic model of the eye, which allows parametrical modification of geometric and material properties. Our main interest is in measuring ONH's potential damage in ocular hypertension due to intracranial pressure. Simulation results indicate a significant role of ICP in post-laminar neural tissue failure and a possible role of central corneal thickness (CCT) and scleral modulus in clinical assessment and treatment of patients with ocular hypertension (OHT). Specifically, CCT was found to affect ONH at early stages of damage in ocular hypertension conditions, and high scleral modulus seems to result in reduced shear failure in lamina cribrosa in a similar OHT state. These findings suggest that CCT could be a risk factor for glaucoma in OHT patients at initial stage along with cornea stiffness. Graphical abstract Graphical abstract. [ABSTRACT FROM AUTHOR]

In order to investigate the aqueous humor flow based on the coupling effects of fluid–solid–heat under different ocular pressure, four models of rabbit eye were constructed and multi-field coupling vs. fluid–solid interaction was compared in these models. ADINA software was applied to mimic the aqueous humor flow. The contour of temperature demonstrates multiple peaks with larger value near the pupil. The flow pattern is influenced mainly by the variation of ocular pressure. It is necessary to perform multi-field coupling simulation based on dynamic pressure measurement when studying the aqueous humor flow in eyes. [ABSTRACT FROM AUTHOR]

AIM: To analyse ocular biomechanical properties, central corneal thickness (CCT) and intraocular pressure (IOP) in post-keratoplasty eyes, as compared to normal subjects, with a new Scheimpflug-based technology. Moreover, biomechanical data were correlated with the size and age of the donor and recipient corneas. METHODS: Measurements were conducted on 46 eyes of 46 healthy patients without any corneal pathology (age: 53.83±20.8y) and 30 eyes of 28 patients after penetrating keratoplasty (age: 49.43±21.34y). Ten biomechanical parameters, the CCT and IOP were recorded by corneal visualization scheimpflug technology (CorVis ST) using high-speed Scheimpflug imaging. Keratometry values were also recorded using Pentacam HR system. Scheimpflug measurements were performed after 43.41±40.17mo (range: 11-128mo) after the keratoplasty and after 7.64±2.34mo (range: 5-14mo) of suture removal. RESULTS: Regarding the device-specific biomechanical parameters, the highest concavity time and radius values showed a significant decrease between these two groups (P=0.01 and P

Despite the fact that the eye represents a challenge for biomechanical research due to its size, over the last two decades, much data on ocular biomechanics were accumulated. Scleral and lamina cribrosa biomechanics contribute to our understanding of myopia and open-angle glaucoma; iris and trabecular meshwork biomechanics to that of angle-closure glaucoma; vitreous biomechanics to that of retinal detachment and ocular drug delivery; corneal biomechanics to that of keratoconus; and lens capsule biomechanics to that of cataract. This paper offers a general overview of recent advances in corneal, scleral, crystalline lens, and lamina cribrosa biomechanics and summarizes the results of experimental and clinical studies. Ocular biomechanics abnormalities affect etiology of many eye diseases. Ocular biomechanics plays an important role in the development of novel diagnostic methods, therapeutic and surgical procedures. Corneal biomechanics impacts etiology and pathogenesis of keratoconus as well as tonometry accuracy and explains corneal refractive surgery effect. Scleral biomechanics is associated with IOP and progressive myopia. Accommodative apparatus (ciliary body and crystalline lens) is an important anatomic physiological structure. Recent studies uncovered the causes of agerelated loss of accommodation as a result of lens involution. Optic nerve head abnormalities due to IOP fluctuations are the key factor of glaucomatous neuropathy. They are directly associated with ocular biomechanics as well.