Abstract
PurposeTo investigate a relationship between birefringence and elasticity of porcine sclera ex vivo using polarization-sensitive optical coherence tomography (PS-OCT).MethodsElastic parameters and birefringence of 19 porcine eyes were measured. Four pieces of scleral strips which were parallel to the limbus, with a width of 4 mm, were dissected from the optic nerve head to the temporal side of each porcine eye. Birefringence of the sclera was measured with a prototype PS-OCT. The strain and force were measured with a uniaxial material tester as the sample was stretched with a speed of 1.8 mm/min after preconditioning. A derivative of the exponentially-fitted stress-strain curve at 0% strain was extracted as the tangent modulus. Power of exponential stress-strain function was also extracted from the fitting. To consider a net stiffness of sclera, structural stiffness was calculated as a product of tangent modulus and thickness. Correlations between birefringence and these elastic parameters were examined.ResultsStatistically significant correlations between birefringence and all of the elastic parameters were found at 2 central positions. Structural stiffness and power of exponential stress-strain function were correlated with birefringence at the position near the optic nerve head. No correlation was found at the position near the equator.ConclusionsThe evidence of correlations between birefringence and elasticity of sclera tested uniaxially was shown for the first time. This work may become a basis for in vivo measurement of scleral biomechanics using PS-OCT.
Highlights
The elasticity of the collagen matrix in many types of tissues supports the biomechanical properties of organs
It has been known that the sclera of the eye has a significant role in the development and progress of myopia and glaucoma, [1,2] it has proven difficult to measure scleral biomechanics noninvasively
We demonstrate that scleral elasticity is associated with its birefringence, which can be measured using polarization-sensitive optical coherence tomography (PS-OCT)
Summary
The elasticity of the collagen matrix in many types of tissues supports the biomechanical properties of organs. [3] We analyze the birefringence and elasticity of porcine sclera, and show correlations among these parameters This technology for optical rheology is potentially applicable to the in vivo assessment of biomechanical properties of fibrous connective tissues, and may be a useful tool for investigating the progression of tissue remodeling. In eyes with glaucoma, which is the second leading cause of blindness in the world, [6] the mechanical properties of the sclera have been considered to affect individual tolerance to intraocular pressurerelated damage to the retinal nerve fibers [2]. Both increased stiffness and hypercompliance of the sclera have been reported in eyes with glaucoma. Both increased stiffness and hypercompliance of the sclera have been reported in eyes with glaucoma. [7,8,9,10,11,12] Despite the importance of the scleral biomechanics for ocular diseases, it has been investigated only with ex vivo experiments and computer simulations because of the difficulty of obtaining in vivo measurements
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