A comparison of the elastic properties of human choroid and sclera

Friberg, Thomas R.; Lace, John W.

doi:10.1016/0014-4835(88)90053-x

Cited by 223 publications

(164 citation statements)

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“…The scleral modulus at this point is around 1.2-1.3 Mpa, which is close to the reported values of scleral moduli measured from strips of human sclera (1.8 MPa: posterior sclera and 2.9 MPa: anterior sclera). 30 The models were tested for what is considered a normal, healthy IOP (16 mmHg) as well for low and excessively high IOP values. In the clinical situation, an IOP of 32 mmHg would arouse suspicion of glaucoma but even at a level which is considered pathological, vision may be unaffected suggesting that some selfadjustment of the eyeball may occur.…”

Section: Discussionmentioning

confidence: 99%

Modelling the elastic properties of the anterior eye and their contribution to maintenance of image quality: the role of the limbus

Asejczyk-Widlicka

Sródka

Kasprzak

et al. 2006

Eye

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Purpose The elastic moduli of the cornea, sclera, and limbus for different corneal eccentricities (e) and varying levels of intraocular pressure (IOP) were modelled in order to determine how the rheological properties, especially those of the limbus, need to alter to maintain optical image quality when the eye is subjected to small variations in IOP. Methods Finite element analysis (FEA) was used to construct eyeball models with four different corneal eccentricities (e ¼ 0, 0.33, 0.5, 0.65). Three values for Young's modulus of the cornea were tested in all models (0.2 megapascal (MPa), 1.2 and 10 MPa). For each corneal modulus, scleral moduli of 3, 4, 5, 7, and 10 times that of the corneal modulus were selected. The limbal modulus was varied to optimise image quality of the eye model subjected to IOP variations of 70.8 mmHg for three different levels of IOP (8,16, and 32 mmHg). Results The elastic modulus of the limbal ring increases with an increase in corneal modulus and rises to a peak when the ratio of scleral to corneal moduli is between 5 and 7 depending on corneal eccentricity. Different levels of IOP produce only slight differences in the relative moduli required to maintain optical image quality. Conclusions The significance of a peak in the value of Young's modulus of the limbus is not clear but suggests that there may be an optimal limbal modulus that must be balanced with the moduli of cornea and sclera for preservation of image quality.

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Section: Discussionmentioning

confidence: 99%

Modelling the elastic properties of the anterior eye and their contribution to maintenance of image quality: the role of the limbus

Asejczyk-Widlicka

Sródka

Kasprzak

et al. 2006

Eye

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“…Sclera mechanical properties have been characterized on dissected tissue specimens using uniaxial [11][12][13][14][15][16] or biaxial mechanical tests [17]. These studies have demonstrated that the mechanical behavior of the sclera is typically nonlinear, viscoelastic and anisotropic.…”

Section: Introductionmentioning

confidence: 99%

Ultrasonic Measurement of Scleral Cross-Sectional Strains During Elevations of Intraocular Pressure: Method Validation and Initial Results in Posterior Porcine Sclera

Tang

Liu

2012

Journal of Biomechanical Engineering

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Background. Scleral biomechanical properties may be important in the pathogenesis and progression of glaucoma. The goal of this study is to develop and validate an ultrasound method for measuring cross-sectional distributive strains in the sclera during elevations of intraocular pressure (IOP). Method of Approach. Porcine globes (n ¼ 5) were tested within 24 hs postmortem. The posterior scleral shells were dissected and mounted onto a custom-built pressurization chamber. A high-frequency (55-MHz) ultrasound system (Vevo660, VisualSonics Inc., Toronto) was employed to acquire the radio frequency data during scans of the posterior pole along both circumferential and meridian directions. The IOP was gradually increased from 5 to 45 mmHg. The displacement fields were obtained from correlation-based ultrasound speckle tracking. A least-square strain estimator was used to calculate the strains in both axial and lateral directions. Experimental validation was performed by comparing tissue displacements calculated from ultrasound speckle tracking with those induced by an actuator. Theoretical analysis and simulation experiments were performed to optimize the ultrasound speckle tracking method and evaluate the accuracy and signal-to-noise ratio (SNR) in strain estimation. Results. Porcine sclera exhibited significantly larger axial strains (e.g., À5.1 6 1.5% at 45 mmHg, meridian direction) than lateral strains (e.g., 2.2 6 0.7% at 45 mmHg, meridian direction) during IOP elevations (P's < 0.01). The strain magnitudes increased nonlinearly with pressure increase. The strain maps displayed heterogeneity through the thickness. The lateral strains were significantly smaller in the circumferential direction than the meridian direction at 45 mmHg (P < 0.05). Experimental validation showed that the ultrasound speckle tracking method was capable of tracking displacements at the accuracy of sub-micron to micron. Theoretical analysis predicted the dependence of the strain estimation SNR on the strain level, as well as signal processing parameters such as kernel size. Simulation results showed that ultrasound speckle tracking had a high accuracy for estimating strains of 1-5% and a high SNR for strains of 0.5-5%. Conclusions. A new experimental method based on ultrasound speckle tracking has been developed for obtaining cross-sectional strain maps of the posterior sclera. This method provides a useful tool to examine distributive strains through the thickness of the sclera during elevations of IOP.

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“…Although attempts to study the properties of sclera have been made by several researchers [10][11][12][13]18,19], little work has been done to quantify these data in a form consistent with linear viscoelastic theory. All studies to date report a nonlinear stress-strain relationship, as well as creep or stress relaxation behavior.…”

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confidence: 99%

Viscoelastic Characterization of Peripapillary Sclera: Material Properties by Quadrant in Rabbit and Monkey Eyes

Downs

Suh

Thomas

et al. 2003

Journal of Biomechanical Engineering

113

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In this report we characterize the viscoelastic material properties of peripapillary sclera from the four quadrants surrounding the optic nerve head in both rabbit and monkey eyes. Scleral tensile specimens harvested from each quadrant were subjected to uniaxial stress relaxation and tensile ramp to failure tests. Linear viscoelastic theory, coupled with a spectral reduced relaxation function, was employed to characterize the viscoelastic properties of the tissues. We detected no differences in the stressstrain curves of specimens from the four quadrants surrounding the optic nerve head (ONH) below a strain of 4 percent in either the rabbit or monkey. While the peripapillary sclera from monkey eyes is significantly stiffer (both instantaneously and in equilibrium) and relaxes more slowly than that from rabbits, we detected no differences in the viscoelastic material properties (tested at strains of 0-1 percent) of sclera from the four quadrants surrounding the ONH within either species group.Glaucomatous optic neuropathy is one of the three leading causes of blindness in the US [1,2] and is the result of damage to the neural tissues of the optic nerve head (ONH). Its clinical hallmarks are posterior cupping (bowing back) of the surface of the ONH, and a characteristic pattern of visual field loss.Corresponding Author: J. Crawford Downs, PhD, Department of Biomedical Engineering, Tulane University, Lindy Boggs Center, Suite 500, New Orleans, LA 70118; Tel: (504) 865-5897; fax: (504) NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptWhile IOP-lowering is central to the treatment of the disease [2,3], there is wide disagreement over the role of IOP in the development and progression of glaucoma [3][4][5]. Much of the confusion over the role of IOP in glaucoma stems from two groups of patients: those exhibiting ocular hypertension (elevated IOP) that never develop the disease, and those that develop glaucoma with no measurable increase in IOP (normal tension glaucoma).The sclera is the principal load-bearing tissue of the eye and consists primarily of collagen. The primary function of the sclera is to resist intraocular pressure, provide attachment sites for the ocular musculature and support the retina in the spheroid shape necessary for focused vision. The thickness and predominant collagen fibril orientation of this tissue are dependent on location in the globe [6][7][8][9]. However, whether the fibril orientation has a large effect on scleral material properties remains controversial [6,[10][11][12][13].The scleral shell is pierced by the scleral canal, an elliptical hole (1-2.5 mm in diameter) in the posterior portion of the globe, through which the retinal ganglion cell axons pass on their path to form the orbital optic nerve (Fig. 1). The scleral canal is spanned by a series of thin, fenestrated connective tissue sheets known as the lamina cribrosa (Fig. 1B, 1C). The lamina cribrosa provides structural and nutritional support to the retinal ganglion cell axons as they pass ...

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A comparison of the elastic properties of human choroid and sclera

Cited by 223 publications

References 5 publications

Modelling the elastic properties of the anterior eye and their contribution to maintenance of image quality: the role of the limbus

Modelling the elastic properties of the anterior eye and their contribution to maintenance of image quality: the role of the limbus

Ultrasonic Measurement of Scleral Cross-Sectional Strains During Elevations of Intraocular Pressure: Method Validation and Initial Results in Posterior Porcine Sclera

Viscoelastic Characterization of Peripapillary Sclera: Material Properties by Quadrant in Rabbit and Monkey Eyes

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