Viscoelastic Material Properties of the Peripapillary Sclera in Normal and Early-Glaucoma Monkey Eyes

Downs, J. Crawford; Jk, Suh; Ka, Thomas; Aj, Bellezza; Hart, Richard T.; Burgoyne, Claude F.

doi:10.1167/iovs.04-0114

Cited by 228 publications

(185 citation statements)

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“…Peripapillary sclera has been extensively investigated, because it is known to play an important role in the deformation of lamina cribrosa [47]. Since the stiffness of the peripapillary sclera of glaucomatous eyes was different from that of normal eyes in the cases of experimental monkeys and postmortem humans [7][8][9][10], it is likely that the stiffness of the peripapillary sclera is related to the progression of glaucoma. In the future, it would be interesting to investigate birefringence of peripapillary sclera in normal and glaucomatous eyes using PS-OCT especially designed for posterior segment imaging [28,48,49].…”

Section: Discussionmentioning

confidence: 99%

“…Although the alignment of scleral collagen fibers in glaucomatous eyes is not known well, Pijanka et al reported that sclerae of some glaucomatous eyes had decreased fiber anisotropy of collagen fibers in two quadrant sectors around the optic nerve head [6]. The stiffness of the peripapillary sclera of glaucomatous eyes was different from that of normal eyes in the cases of experimental monkeys and postmortem humans [7][8][9][10]. Glaucomatous human eyes had lower density of collagen fibers in peripapillary sclera than that of normal human eyes [11].…”

Section: Introductionmentioning

confidence: 99%

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Scleral birefringence as measured by polarization-sensitive optical coherence tomography and ocular biometric parameters of human eyes in vivo

Yamanari

Nagase

Fukuda

et al. 2014

Biomed. Opt. Express

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Abstract:The relationship between scleral birefringence and biometric parameters of human eyes in vivo is investigated. Scleral birefringence near the limbus of 21 healthy human eyes was measured using polarizationsensitive optical coherence tomography. Spherical equivalent refractive error, axial eye length, and intraocular pressure (IOP) were measured in all subjects. IOP and scleral birefringence of human eyes in vivo was found to have statistically significant correlations (r = −0.63, P = 0.002). The slope of linear regression was −2.4 × 10 −2 deg/μm/mmHg. Neither spherical equivalent refractive error nor axial eye length had significant correlations with scleral birefringence. To evaluate the direct influence of IOP to scleral birefringence, scleral birefringence of 16 ex vivo porcine eyes was measured under controlled IOP of 5−60 mmHg. In these ex vivo porcine eyes, the mean linear regression slope between controlled IOP and scleral birefringence was −9.9 × 10 −4 deg/μm/mmHg. In addition, porcine scleral collagen fibers were observed with second-harmonic-generation (SHG) microscopy. SHG images of porcine sclera, measured on the external surface at the superior side to the cornea, showed highly aligned collagen fibers parallel to the limbus. In conclusion, scleral birefringence of healthy human eyes was correlated with IOP, indicating that the ultrastructure of scleral collagen was correlated with IOP. It remains to show whether scleral collagen ultrastructure of human eyes is affected by IOP as a long-term effect. ©2014 Optical Society of America References and links1. N. A. McBrien and A. Gentle, "Role of the sclera in the development and pathological complications of myopia," Prog. Retin. Eye Res. 22(3), 307-338 (2003). 2. C. F. Burgoyne, J. C. Downs, A. J. Bellezza, J. K. Suh, and R. T. Hart, "The optic nerve head as a biomechanical structure: a new paradigm for understanding the role of IOP-related stress and strain in the pathophysiology of glaucomatous optic nerve head damage," Prog. Retin. Eye Res. 24(1), 39-73 (2005). 3. J. A. Rada, S. Shelton, and T. T. Norton, "The sclera and myopia," Exp. Eye Res. 82(2), 185-200 (2006). 4. J. T. Siegwart, Jr. and T. T. Norton, "Regulation of the mechanical properties of tree shrew sclera by the visual environment," Vision Res. 39(2), 387-407 (1999 1714-1728 (2012) C. So, and C.-Y. Dong, "Multiphoton autofluorescence and second-harmonic generation imaging of the ex vivo porcine eye," Invest.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Scleral birefringence as measured by polarization-sensitive optical coherence tomography and ocular biometric parameters of human eyes in vivo

Yamanari

Nagase

Fukuda

et al. 2014

Biomed. Opt. Express

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“…The peripapillary sclera of human glaucomatous eyes has a lower creep rate and higher stiffness compared with that of normal eyes in inflation tests [15]. In a monkey model of glaucoma, the posterior sclera also exhibits a higher stiffness under inflation [16] and the peripapillary sclera shows a higher equilibrium modulus after stress relaxation following a rapid deformation, but no change in the time-dependent parameters compared with that of normal eyes in uniaxial strip tests [17]. The posterior sclera of human myopic eyes reaches a higher strain at maximum pressure than that of normal eyes under uniaxial testing [18].…”

Section: Introductionmentioning

confidence: 99%

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera

Murienne

Chen

Quigley

et al. 2016

J. R. Soc. Interface.

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We characterized the structural and mechanical changes after experimental digestion of sulfated glycosaminoglycans (s-GAGs) in the human posterior sclera, using ultrasound thickness measurements and an inflation test with three-dimensional digital image correlation (3D-DIC). Each scleral specimen was first incubated in a buffer solution to return to full hydration, inflation tested, treated in a buffer solution with chondroitinase ABC (ChABC), then inflation tested again. After each test series, the thickness of eight locations was measured. After enzymatic treatment, the average scleral thickness decreased by 13.3% ( p , 0.001) and there was a stiffer overall stress-strain response ( p , 0.05). The stress-strain response showed a statistically significant increase in the low-pressure stiffness, high-pressure stiffness and hysteresis. Thus, s-GAGs play a measurable role in the mechanical behaviour of the posterior human sclera.

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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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Viscoelastic Material Properties of the Peripapillary Sclera in Normal and Early-Glaucoma Monkey Eyes

Cited by 228 publications

References 19 publications

Scleral birefringence as measured by polarization-sensitive optical coherence tomography and ocular biometric parameters of human eyes in vivo

Scleral birefringence as measured by polarization-sensitive optical coherence tomography and ocular biometric parameters of human eyes in vivo

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera

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

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