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A special issue of International Journal of Environmental Research and Public Health (ISSN 1660-4601). This special issue belongs to the section "Global Health".

Deadline for manuscript submissions: closed (30 September 2019) | Viewed by 20082

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Special Issue Editors

Prof. Ahmed Elsheikh

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Guest Editor

1. School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
2. NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London EC1V 2PD, UK
3. School of Biological Science and Biomedical Engineering, Beihang University, Beijing 100083, China
Interests: Material characterisation of ocular tissue; Numerical simulation of ocular biomechanical performance; Development of medical devices to improve management of eye conditions

Dr. Riccardo Vinciguerra

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Guest Editor

1. St. Paul’s Eye Unit, Royal Liverpool University Hospital, Liverpool L7 8XP, UK
2. School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
3. Istituto Universitario Fernandez Vega, 33012 Oviedo, Spain
Interests: Ocular biomechanics, keratoconus detection and treatment, refractive surgery, corneal collagen cross-linking, models of regression after refractive surgery ablation and corneal transplants., glaucoma

Special Issue Information

Dear Colleagues,

The evaluation of ocular biomechanics, over the last two decades, has led to improved understanding of pathologies affecting the anterior and posterior segments of the eye. Diseases such as keratoconus and iatrogenic ectasia have been shown to be associated with a focal deterioration in corneal biomechanics and this association has enabled the development of treatments including collagen cross-linking (CXL) and intra-corneal ring implants to stiffen the cornea and hence halt the progression of ectasia. However, the accurate evaluation of corneal biomechanics and the biomechanical effect of CXL and intracorneal ring implantation is highly desirable as a necessary pre-requisite for the optimization of these treatment regimes.

Ocular biomechanics are also important in the field of glaucoma. A number of studies have shown that biomechanics are associated with progressive visual field loss in certain forms of glaucoma. In addition, corneal biomechanical properties, in particular stiffness, are among the strongest predictors of IOP measurement error, after corneal thickness. This appreciation of their effect had led to the development of better and more accurate IOP correction formulas than those based on the central corneal thickness alone.

In this Special Issue, we aim to gather together high-quality articles mainly focused on the assessment of ocular biomechanics and their effect on the development and progression of ocular diseases. We are particularly interested in articles focused on the evaluation of corneal biomechanics in vivo, and the role they play in the progression of glaucoma, keratoconus and other forms of ectasia. Furthermore, the Special Issue will have a part dedicated to corneal biomechanics after the CXL procedure and the intra-corneal rings and refractive surgeries.

Potential topics include but are not limited to the following:

Evaluation of corneal biomechanics in vivo
Change in corneal biomechanics post-refractive surgery
Corneal biomechanics after corneal collagen cross-linking and intracorneal ring implantation
Numerical simulation of corneal biomechanics
Corneal biomechanics in glaucoma and other ocular pathologies
Intraocular pressure measurement and the influence of corneal biomechanics
Corneal biomechanics to assist in the diagnosis of ectasia and glaucoma
Association between the biomechanical properties of the cornea and sclera

Prof. Ahmed Elsheikh
Dr. Riccardo Vinciguerra
Guest Editors

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Keywords

Corneal biomechanics
Corneal collagen cross-linking
Keratoconus
Ectasia
Glaucoma
Refractive surgery
Intracorneal rings
Numerical simulation
Intraocular pressure

Published Papers (6 papers)

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Research

17 pages, 6227 KiB

Open AccessArticle

The Role of Corneal Biomechanics for the Evaluation of Ectasia Patients

by Marcella Q. Salomão, Ana Luisa Hofling-Lima, Louise Pellegrino Gomes Esporcatte, Bernardo Lopes, Riccardo Vinciguerra, Paolo Vinciguerra, Jens Bühren, Nelson Sena, Jr., Guilherme Simões Luz Hilgert and Renato Ambrósio, Jr.

Int. J. Environ. Res. Public Health 2020, 17(6), 2113; https://doi.org/10.3390/ijerph17062113 - 23 Mar 2020

Cited by 45 | Viewed by 3754

Abstract

Purpose: To review the role of corneal biomechanics for the clinical evaluation of patients with ectatic corneal diseases. Methods: A total of 1295 eyes were included for analysis in this study. The normal healthy group (group N) included one eye randomly selected from 736 patients with healthy corneas, the keratoconus group (group KC) included one eye randomly selected from 321 patients with keratoconus. The 113 nonoperated ectatic eyes from 125 patients with very asymmetric ectasia (group VAE-E), whose fellow eyes presented relatively normal topography (group VAE-NT), were also included. The parameters from corneal tomography and biomechanics were obtained using the Pentacam HR and Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). The accuracies of the tested variables for distinguishing all cases (KC, VAE-E, and VAE-NT), for detecting clinical ectasia (KC + VAE-E) and for identifying abnormalities among the VAE-NT, were investigated. A comparison was performed considering the areas under the receiver operating characteristic curve (AUC; DeLong’s method). Results: Considering all cases (KC, VAE-E, and VAE-NT), the AUC of the tomographic-biomechanical parameter (TBI) was 0.992, which was statistically higher than all individual parameters (DeLong’s; p < 0.05): PRFI- Pentacam Random Forest Index (0.982), BAD-D- Belin -Ambrosio D value (0.959), CBI -corneal biomechanical index (0.91), and IS Abs- Inferior-superior value (0.91). The AUC of the TBI for detecting clinical ectasia (KC + VAE-E) was 0.999, and this was again statistically higher than all parameters (DeLong’s; p < 0.05): PRFI (0.996), BAD-D (0.995), CBI (0.949), and IS Abs (0.977). Considering the VAE-NT group, the AUC of the TBI was 0.966, which was also statistically higher than all parameters (DeLong’s; p < 0.05): PRFI (0.934), BAD- D (0.834), CBI (0.774), and IS Abs (0.677). Conclusions: Corneal biomechanical data enhances the evaluation of patients with corneal ectasia and meaningfully adds to the multimodal diagnostic armamentarium. The integration of biomechanical data and corneal tomography with artificial intelligence data augments the sensitivity and specificity for screening and enhancing early diagnosis. Besides, corneal biomechanics may be relevant for determining the prognosis and staging the disease. Full article

(This article belongs to the Special Issue Ocular Biomechanics)

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11 pages, 3440 KiB

Open AccessFeature PaperArticle

Differences in Simulated Refractive Outcomes of Photorefractive Keratectomy (PRK) and Laser In-Situ Keratomileusis (LASIK) for Myopia in Same-Eye Virtual Trials

by Ibrahim Seven, Joshua S. Lloyd and William J. Dupps

Int. J. Environ. Res. Public Health 2020, 17(1), 287; https://doi.org/10.3390/ijerph17010287 - 31 Dec 2019

Cited by 7 | Viewed by 2638

Abstract

The use of computational mechanics for assessing the structural and optical consequences of corneal refractive procedures is increasing. In practice, surgeons who elect to perform PRK rather than LASIK must often reduce the programmed refractive treatment magnitude to avoid overcorrection of myopia. Building on a recent clinical validation study of finite element analysis (FEA)-based predictions of LASIK outcomes, this study compares predicted responses in the validated LASIK cases to theoretical PRK treatments for the same refractive error. Simulations in 20 eyes demonstrated that PRK resulted in a mean overcorrection of 0.17 ± 0.10 D relative to LASIK and that the magnitude of overcorrection increased as a function of attempted correction. This difference in correction closely matched (within 0.06 ± 0.03 D) observed differences in PRK and LASIK from a historical nomogram incorporating thousands of cases. The surgically induced corneal strain was higher in LASIK than PRK and resulted in more forward displacement of the central stroma and, consequently, less relative flattening in LASIK. This FE model provides structural confirmation of a mechanism of action for the difference in refractive outcomes of these two keratorefractive techniques, and the results were in agreement with empirical clinical data. Full article

(This article belongs to the Special Issue Ocular Biomechanics)

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21 pages, 27531 KiB

Open AccessArticle

Simulation of Air Puff Tonometry Test Using Arbitrary Lagrangian–Eulerian (ALE) Deforming Mesh for Corneal Material Characterisation

by Osama Maklad, Ashkan Eliasy, Kai-Jung Chen, Vassilios Theofilis and Ahmed Elsheikh

Int. J. Environ. Res. Public Health 2020, 17(1), 54; https://doi.org/10.3390/ijerph17010054 - 19 Dec 2019

Cited by 18 | Viewed by 5269

Abstract

Purpose: To improve numerical simulation of the non-contact tonometry test by using arbitrary Lagrangian-Eulerian deforming mesh in the coupling between computational fluid dynamics model of an air jet and finite element model of the human eye. Methods: Computational fluid dynamics model simulated impingement of the air puff and employed Spallart–Allmaras model to capture turbulence of the air jet. The time span of the jet was 30 ms and maximum Reynolds number was

R_{e} = 2.3 \times 10^{4}

, with jet orifice diameter 2.4 mm and impinging distance 11 mm. The model of the human eye was analysed using finite element method with regional hyperelastic material variation and corneal patient-specific topography starting from stress-free configuration. The cornea was free to deform as a response to the air puff using an adaptive deforming mesh at every time step of the solution. Aqueous and vitreous humours were simulated as a fluid cavity filled with incompressible fluid with a density of 1000 kg/m³. Results: Using the adaptive deforming mesh in numerical simulation of the air puff test improved the traditional understanding of how pressure distribution on cornea changes with time of the test. There was a mean decrease in maximum pressure (at corneal apex) of 6.29 ± 2.2% and a development of negative pressure on a peripheral corneal region 2–4 mm away from cornea centre. Conclusions: The study presented an improvement of numerical simulation of the air puff test, which will lead to more accurate intraocular pressure (IOP) and corneal material behaviour estimation. The parametric study showed that pressure of the air puff is different from one model to another, value-wise and distribution-wise, based on cornea biomechanical parameters. Full article

(This article belongs to the Special Issue Ocular Biomechanics)

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8 pages, 2568 KiB

Open AccessArticle

Topographic and Biomechanical Changes after Application of Corneal Cross-Linking in Recurrent Keratoconus

by Emilio Pedrotti, Grazia Caldarella, Adriano Fasolo, Erika Bonacci, Nicola Gennaro, Alessandra De Gregorio and Giorgio Marchini

Int. J. Environ. Res. Public Health 2019, 16(20), 3872; https://doi.org/10.3390/ijerph16203872 - 12 Oct 2019

Cited by 10 | Viewed by 2480

Abstract

Background: Recurrent keratoconus (RKC) develops as a progressive thinning of the peripheral and the inferior cornea after keratoplasty, in both graft and host, causing secondary astigmatism, refractive instability, and reduced visual acuity. We evaluated the effectiveness of corneal cross-linking (CXL) in patients diagnosed with RKC. Methods: Accelerated-CXL via the epi-off technique was performed in15 patients (18 eyes) diagnosed with RKC. Topographic and biomechanical changes were assessed at 12 months. Results: Differences in maximum keratometry, thinnest corneal thickness, and biomechanical parameters (deformation amplituderatio, inverse concave radius, applanation 1 velocity, and applanation 2 velocity, stiffness A1) versus baseline were statistically significant (p < 0.05).Best corrected visual acuity was improved in 13 eyes and unchanged in 4;manifest refractive spherical equivalent was reduced in 13 eyes, increased in 3,and unchanged in 1 eye; topographic astigmatism was reduced in 9 eyes, remained stable in 1 eye, and increased in 7 eyes. Conclusions: Improved topographic and biomechanic indexes at 1 year after CXL suggest it‘s potential as first-line therapy for RKC, as it is for KC. Full article

(This article belongs to the Special Issue Ocular Biomechanics)

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16 pages, 6803 KiB

Open AccessArticle

Numerical Simulation of Corneal Fibril Reorientation in Response to External Loading

by Dong Zhou, Ahmed Abass, Ashkan Eliasy, Alexander Movchan, Natalia Movchan and Ahmed Elsheikh

Int. J. Environ. Res. Public Health 2019, 16(18), 3278; https://doi.org/10.3390/ijerph16183278 - 6 Sep 2019

Cited by 1 | Viewed by 2642

Abstract

Purpose: To simulate numerically the collagen fibril reorientation observed experimentally in the cornea. Methods: Fibril distribution in corneal strip specimens was monitored using X-ray scattering while under gradually increasing axial loading. The data were analysed at each strain level in order to quantify the changes in the angular distribution of fibrils with strain growth. The resulting relationship between stain and fibril reorientation was adopted in a constitutive model to control the mechanical anisotropy of the tissue material. The outcome of the model was validated against the experimental measurements before using the model in simplified representations of two surgical procedures. Results: The numerical model was able to reproduce the experimental measurements of specimen deformation and fibril reorientation under uniaxial loading with errors below 8.0%. With tissue removal simulated in a full eye numerical model, fibril reorientation could be predicted around the affected area, and this change both increased with larger tissue removal and reduced gradually away from that area. Conclusion: The presented method can successfully simulate fibril reorientation with changes in the strain regime affecting cornea tissue. Analyses based on this method showed that fibrils tend to align parallel to the tissue cut following keratoplasty operations. With the ability to simulate fibril reorientation, numerical modelling can have a greater potential in modelling the behaviour following surgery and injury to the cornea. Full article

(This article belongs to the Special Issue Ocular Biomechanics)

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10 pages, 2857 KiB

Open AccessArticle

Corneal Buckling during Applanation and Its Effect on the Air Pressure Curve in Ocular Response Analyzer

by Agnieszka Jóźwik, Henryk Kasprzak and Agata Kozakiewicz

Int. J. Environ. Res. Public Health 2019, 16(15), 2742; https://doi.org/10.3390/ijerph16152742 - 31 Jul 2019

Cited by 3 | Viewed by 2118

Abstract

The paper presents, for the first time, corneal buckling, during the air puff applanation, recorded with use of Ocular Response Analyzer (ORA), when the cornea is deeper deformed after its applanation. Precise numerical analysis of the air pressure curve from the raw data, distinct local disturbances of the curve, which appear almost exactly at the time of the first and the second applanations. Thirty measurements taken on six eyes show clear dependencies between times of both applanations and appearances of local wave disturbances on the air pressure curve as well as between the amplitude of pressure wave disturbances and the respective height of applanation curve. These findings can be interpreted as a result of very fast corneal buckling, that produces the air pressure wave, propagating from the cornea towards the device. The quantitative dependencies measured and described in this study, enable to characterize the individual buckling during respective applanations. Due to these individual characterizations and dependencies it is possible to understand and describe better the ultrafast corneal applanation process. Such phenomena could likely be employed to increase the accuracy of measured parameters by ORA or for identifying new types of biomechanical properties of the cornea. Full article

(This article belongs to the Special Issue Ocular Biomechanics)

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