The Influence of Various Substances on the Biomechanical Behavior of Lamina Cribrosa and Peripapillary Sclera

Spoerl, Eberhard; Boehm, Andreas; Pillunat, Lutz E.

doi:10.1167/iovs.04-0978

Cited by 87 publications

(75 citation statements)

References 44 publications

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“…This behavior is in line with the findings from the uniaxial tensile strip tests in which the sclera was shown to have a higher tangent modulus when stressed. [23][24][25] The scleral tangent modulus measured in this study (Ej IOP ¼ 0.20 MPa at 15 mm Hg) was approximately twice that of the corneal tangent modulus measured in our previous study (Ej IOP ¼ 0.12 MPa at 15 mm Hg) using the same indentation technique. 20 This suggested that the sclera is stiffer than the cornea, providing key structural support to the eye.…”

Section: Discussionsupporting

confidence: 63%

Noninvasive Measurement of Scleral Stiffness and Tangent Modulus in Porcine Eyes

Leung

et al. 2014

Invest. Ophthalmol. Vis. Sci.

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PURPOSE. We investigated an indentation technique to measure the scleral stiffness and tangent modulus of porcine eyes. METHODS.The scleral load-displacement responses were measured with a universal testing machine as a function of IOP in 15 porcine eyes ex vivo using a 5-mm diameter cylindrical flatpunch indenter. The scleral radius of curvature and scleral thickness were measured using a DSLR camera (Alpha 900) and a camera-mounted stereomicroscope (M205C), respectively. The relationships between scleral stiffness, tangent modulus, and IOP were examined. RESULTS.The mean local scleral radius of curvature and scleral thickness were 7.86 6 0.49 and 1.03 6 0.14 mm, respectively. The average scleral stiffness and scleral tangent modulus of porcine eyes were 0.13 6 0.02 N/mm and 0.20 6 0.04 MPa at 15 mm Hg, respectively. The scleral stiffness and scleral tangent modulus were correlated positively with IOP (scleral stiffness, 0.989 < r < 0.999, P < 0.001; scleral tangent modulus, 0.989 < r < 0.999, P < 0.001).CONCLUSIONS. The scleral indentation technique can provide a noninvasive approach to measure scleral stiffness and tangent modulus.Keywords: sclera, glaucoma, myopia, tangent modulus, noninvasive measurement T he sclera constitutes over 70% of the outer envelope of the eyeball, has a complex multilayered structure, and has a central role in providing structural stability to the eye. The scleral biomechanical property is an important parameter characterizing the ocular structural integrity. The sclera has been shown to be more flexible and less load-bearing in myopes than in emmetropes. [1][2][3][4][5] It also has been shown that increased ocular rigidity (a measure describing the relationship between the change in IOP and the change in eyeball volume) is associated with the development of glaucoma, 6 and that scleral stiffness is correlated with increased prevalence of glaucoma and age. 7,8 While the importance of scleral properties is recognized, in vivo technique for measurement of the scleral properties is limited. Scleral properties, such as scleral stiffness and tangent modulus, are ascertained from load-displacement curves of the sclera. (Like other biological tissues, the sclera is a complex composite structure with many layers. In investigations of biomechanical properties, the detailed fine structures often are ignored, such that the properties measured are interpreted as the material property of the composite structure 9-11 under small deformation linear elastic regime.) The loads generally are imposed onto the eye using inflation methods, 9,12-17 and displacements are ascertained using speckle interferometry, 9,12,13,17 digital camera imaging, 15,16 or ultrasound speckle tracking.14 These inflation-based methods are destructive to the eye, and are unsuited for use in clinical study on the human eye in vivo.Instead of inflation, surface wave elastometry also can be used to measured elastic properties of the cornea. In surface wave elastometry (Refs. 18 and 19; Dupps W, et al. IOVS 2005;46:ARVO E-Abs...

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Section: Discussionsupporting

confidence: 63%

Noninvasive Measurement of Scleral Stiffness and Tangent Modulus in Porcine Eyes

Leung

et al. 2014

Invest. Ophthalmol. Vis. Sci.

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“…Stress-strain measurements were performed according to standard protocols [17] . Briefly, strips were clamped horizontally with a distance of 3 mm between the clamps of the microcomput- To precondition the strips, stress-strain measurements were performed with a prestress of 10 !…”

Section: Stress-strain Measurementsmentioning

confidence: 99%

“…AGEs were identified in diabetic or ageing ocular tissues including cornea [10] , lens [11] , vitreous [12] , and retina [13] but also in the optic nerve head (ONH) [14][15][16] . Interestingly, a recent in vitro study detected a significant stiffening of the lamina cribrosa and the peripapillary sclera (ppSc) under the influence of AGE metabolites in human and porcine eyes, indicating glucose-related cross-linking effects of AGEs [17] . As changes in biomechanical properties of the ONH and the ppSc are particularly relevant to glaucomatous optic nerve damage [18,19] and since AGE levels have been shown to be significantly higher in diabetics compared to age-matched controls [20] , it is not unreasonable to propose that biomechanical properties of the ONH tissues in diabetics may also be affected.…”

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confidence: 99%

Diabetes Mellitus Affects Biomechanical Properties of the Optic Nerve Head in the Rat

et al. 2011

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Background: To investigate the effect of diabetes on the biomechanical behavior of the optic nerve head (ONH) and the peripapillary sclera (ppSc) in streptozocine-induced diabetic rats. Methods: Diabetes mellitus was induced in 20 Wistar rats using streptozocine. Twenty-five nondiabetic rats served as controls. Eyes were enucleated after 12 weeks and 2 strips of one eye were prepared containing ONH or ppSc. The stress-strain relation was measured in the stress range of 0.05–10 MPa using a biomaterial tester. Results: At 5% strain the stress of the ONH in diabetic rats was 897 ± 295 kPa and in the control group it was 671 ± 246 kPa; there was a significant difference between both groups (p = 0.011). The stress of the diabetic ppSc (574 ± 185 kPa) increased compared to that of the nondiabetic ppSc (477 ± 171 kPa), but this did not reach statistical significance (p = 0.174). The calculated tangent modulus at 5% strain was 11.79 MPa in the diabetic ONH and 8.77 MPa in the nondiabetic ONH; there was a significant difference between both groups (p = 0.006). The calculated tangent modulus at 5% strain was 7.17 MPa in the diabetic ppSc and 6.12 MPa in the nondiabetic ppSc, without a statistically significant difference (p = 0.09). Conclusion: In contrast to the ppSc, the ONH of diabetic rats showed a significant increase in stiffness compared to nondiabetic rats, which might be explained by nonenzymatic collagen cross-linking mediated by advanced glycation end products due to high blood glucose levels in diabetes. Further studies are needed to investigate if these biomechanical changes represent a detrimental risk factor for intraocular pressure regulation in diabetic glaucoma patients.

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“…However, these values are inconsistent among different authors and vary by up to 100-fold for sclera and 1000-fold for cornea. 5,[9][10][11][12][13][14] Few studies have described the compressive elastic moduli of the sclera and cornea. 15 The insertion of needles into soft tissues has been published by several investigators.…”

Section: Introductionmentioning

confidence: 99%

Indentation and needle insertion properties of the human eye

Matthews

Hutnik²,

Hill

et al. 2014

Eye

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The Influence of Various Substances on the Biomechanical Behavior of Lamina Cribrosa and Peripapillary Sclera

Cited by 87 publications

References 44 publications

Noninvasive Measurement of Scleral Stiffness and Tangent Modulus in Porcine Eyes

Noninvasive Measurement of Scleral Stiffness and Tangent Modulus in Porcine Eyes

Diabetes Mellitus Affects Biomechanical Properties of the Optic Nerve Head in the Rat

Indentation and needle insertion properties of the human eye

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