Biomechanics of the Cornea and Sclera

Nguyen, Thao D.

doi:10.1007/978-1-4899-7630-7_14

Cited by 5 publications

(4 citation statements)

References 96 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To account for the non-linear behavior of the tissue, we chose to consider the ocular tissues as hyperelastic, resulting in a non-linear response to increasing IOP. The use of an incompressible neo-Hookean constitutive model is a simplification: the cornea and sclera are complex structures with significant anisotropy (Nguyen, 2016). In this case, the model effectively assumed that the secant modulus is constant regardless of the magnitude of deformation.…”

Section: Discussionmentioning

confidence: 99%

“…Biomechanical markers are being explored to improve screening, diagnosis, and management of diseases such as keratoconus and glaucoma (Liu and Roberts, 2005; Elsheikh et al, 2009; Ruberti et al, 2011; Coudrillier et al, 2012; Tang and Liu, 2012; Hon and Lam, 2013; Metzler et al, 2014; Girard et al, 2015; Sinha Roy et al, 2015; Ariza-Gracia et al, 2016; Roberts, 2016). Biomechanical properties of the sclera are often determined via ex vivo mechanical strip testing or inflation tests (Coudrillier et al, 2012; Geraghty et al, 2012; Girard et al, 2015; Pandolfi and Boschetti, 2015; Nguyen, 2016). However, this destructive method depends on a multitude of factors including tissue hydration and strain rate, and there is a wide range of reported values in the literature on the value of Young's modulus of the sclera (Coudrillier et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Biomechanical Impact of the Sclera on Corneal Deformation Response to an Air-Puff: A Finite-Element Study

Nguyen

Roberts

Reilly

2019

Front. Bioeng. Biotechnol.

View full text Add to dashboard Cite

Aim or Purpose: To describe the effect of varying scleral stiffness on the biomechanical deformation response of the cornea under air-puff loading via a finite-element (FE) model.Methods: A two-dimensional axisymmetric stationary FE model of the whole human eye was used to examine the effects varying scleral stiffness and intraocular pressure (IOP) on the maximum apical displacement of the cornea. The model was comprised of the cornea, sclera, vitreous, and surrounding air region. The velocity and pressure profiles of an air-puff from a dynamic Scheimpflug analyzer were replicated in the FE model, and the resultant profile was applied to deform the cornea in a multiphysics study (where the air-puff was first simulated before being applied to the corneal surface). IOP was simulated as a uniform pressure on the globe interior. The simulation results were compared to data from ex vivo scleral stiffening experiments with human donor globes.Results: The FE model predicted decreased maximum apical displacement with increased IOP and increased ratio of scleral-to-corneal Young's moduli. These predictions were in good agreement (within one standard deviation) with findings from ex vivo scleral stiffening experiments using human donor eyes. These findings demonstrate the importance of scleral material properties on the biomechanical deformation response of the cornea in air-puff induced deformation.Conclusion: The results of an air-puff induced deformation are often considered to be solely due to IOP and corneal properties. The current study showed that the stiffer the sclera, the greater will be the limitation on corneal deformation, separately from IOP. This may have important clinical implications to interpreting the response of the cornea under air-puff loading in pathologic conditions.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Biomechanical Impact of the Sclera on Corneal Deformation Response to an Air-Puff: A Finite-Element Study

Nguyen

Roberts

Reilly

2019

Front. Bioeng. Biotechnol.

View full text Add to dashboard Cite

show abstract

“…The PGZ from NSs permeates less through the cornea than sclera, showing that the cornea has a barrier effect three times higher than the sclera (30). This is a consequence of the cornea having a regular cellular order, while the cells of the sclera have a more irregular cellular arrangement (31). Another factor is the physicochemical properties of the molecule, which better interacts with scleral tissue, as well as other molecule properties favoring good scleral permeability, such as Triamcinolone (32).…”

Section: Ex Vivo Permeation Studiesmentioning

confidence: 99%

Optimization, Biopharmaceutical Profile and Therapeutic Efficacy of Pioglitazone-loaded PLGA-PEG Nanospheres as a Novel Strategy for Ocular Inflammatory Disorders

et al. 2018

View full text Add to dashboard Cite

show abstract

“…Fourth, collagen fibers of the corneoscleral shell are interwoven. (Gogola et al, 2018b;Komai and Ushiki, 1991;Lee et al, 2022;Meek, 2009;Morishige et al, 2007;Nguyen, 2016) We and others have demonstrated that collagen interweaving plays an important role in determining the structural stiffness of ocular connective tissues. (Pandolfi et al, 2019;Petsche and Pinsky, 2013;Wang et al, 2020;Winkler et al, 2011) However, such interweaving was not considered in our constitutive model.…”

Section: Discussionmentioning

confidence: 98%

Who bears the load? IOP-induced collagen fiber recruitment over the corneoscleral shell

Foong

Hua

Amini

et al. 2022

Preprint

View full text Add to dashboard Cite

Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In recruitment, as the tissues stretch the constitutive collagen fibers lose their natural waviness, progressively straightening. Recruited, straight, fibers bear substantially more mechanical load than non-recruited, wavy, fibers. As such, the process of recruitment underlies the well-established nonlinear macroscopic behavior of the corneoscleral shell. Recruitment has an interesting implication: when recruitment is incomplete, only a fraction of the collagen fibers is actually contributing to bear the loads, with the rest remaining in reserve. In other words, at a given intraocular pressure (IOP), it is possible that not all the collagen fibers of the cornea and sclera are actually contributing to bear the loads. To the best of our knowledge, the fraction of corneoscleral shell fibers recruited and contributing to bear the load of IOP has not been reported. Our goal was to obtain regionally-resolved estimates of the fraction of corneoscleral collagen fibers recruited and in reserve. We developed a fiber-based microstructural constitutive model that could account for collagen fiber undulations or crimp via their tortuosity. We used experimentally-measured collagen fiber crimp tortuosity distributions in human eyes to derive region-specific nonlinear hyperelastic mechanical properties. We then built a three-dimensional axisymmetric model of the globe, assigning region-specific mechanical properties and regional anisotropy. The model was used to simulate the IOP-induced shell deformation. The model-predicted tissue stretch was then used to quantify collagen recruitment within each shell region. The calculations showed that, at low IOPs, collagen fibers in the posterior equator were recruited the fastest, such that at a physiologic IOP of 15 mmHg, over 90% of fibers were recruited, compared with only a third in the cornea and the peripapillary sclera. The differences in recruitment between regions, in turn, mean that at a physiologic IOP the posterior equator had a fiber reserve of only 10%, whereas the cornea and peripapillary sclera had two thirds. At an elevated IOP of 50 mmHg, collagen fibers in the limbus and the anterior/posterior equator were almost fully recruited, compared with 90% in the cornea and the posterior sclera, and 75% in the peripapillary sclera and the equator. That even at such an elevated IOP not all the fibers were recruited suggests that there are likely other conditions that challenge the corneoscleral tissues even more than IOP. The fraction of fibers recruited may have other potential implications. For example, fibers that are not bearing loads may be more susceptible to enzymatic digestion or remodeling. Similarly, it may be possible to control tissue stiffness through the fraction of recruited fibers without the need to add or remove collagen.

show abstract

Biomechanics of the Cornea and Sclera

Cited by 5 publications

References 96 publications

Biomechanical Impact of the Sclera on Corneal Deformation Response to an Air-Puff: A Finite-Element Study

Biomechanical Impact of the Sclera on Corneal Deformation Response to an Air-Puff: A Finite-Element Study

Optimization, Biopharmaceutical Profile and Therapeutic Efficacy of Pioglitazone-loaded PLGA-PEG Nanospheres as a Novel Strategy for Ocular Inflammatory Disorders

Who bears the load? IOP-induced collagen fiber recruitment over the corneoscleral shell

Contact Info

Product

Resources

About