Study On The Regional Mechanical Properties Of Sclera

The occurrence and development of eye diseases such as myopia and glaucoma are closely related to changes of the biomechanical properties of sclera.Compared with the normal human sclera,the scleral collagen fibers in high myopia exhibit smaller diameters,disordered arrangement,and changed biomechanical properties of sclera,resulting in big deformation under the complex environment of the eye,as well as the extended eye axis and the change of vision.Studying on the mechanical properties of the sclera is of great significance in revealing the pathogenesis of ocular diseases including myopia.The axial tensile method is widely used to analyze the mechanical properties of the sclera in current study.However,the force on sclera in vivo is anisotropic,and the inherent curvature of sclera was destroyed under axial tension.In addition,the mechanical properties of sclera were achieved under larger load in most of the current studies,which could not reflect the force on sclera under physiological conditions.The indentation test is a common method for measuring the mechanical properties of materials.Compared with the axial tensile method,it can keep the integrity of tissues and approach to the real physiological state.However,there is no systematic report on the biomechanical properties of different regions of sclera by indentation method.In this study,the porcine sclera was used to test the mechanical properties including the stiffness and elastic capillary force in different regions by indentation method.Besides,the effects of the indentation rate and different intraocular pressure on the mechanical properties of sclera were systematically analyzed.Furthermore,the content and structure of collagen in different regions of sclera were compared to discuss the reasons for the different mechanical properties of different regions of sclera.This study can provide reference for the accurate modeling of eye movement and the in-depth elucidation of the pathogenesis of eye diseases such as myopia and glaucoma.The main work and conclusions of this study are as follows:1.The porcine sclera was divided into the anterior,equatorial and posterior regions from the corneal end to the optic nerve in the axial direction.The mechanical properties of the sclera in different regions under common intraocular pressure(17 mmHg)were studied.The main results were concluded as follows: The overall stiffness of the anterior sclera was the largest,followed by the equatorial sclera,and the posterior sclera was the smallest within the normal physiological load range.It was consistent with elastic modulus obtained by the uniaxial tensile method,indicating that the posterior sclera was more prone to deformation.The stiffness of different sclera regions increased with the increase of the indentation rate.Besides,the scleral elastic capillary force and surface tension were in the order of large to small: posterior sclera,equatorial sclera,anterior sclera.2.The mechanical properties of the sclera under normal eye pressure and high intraocular pressure(40 mmHg,80 mmHg)were compared by indentation test to analyze the effect of high intraocular pressure on the mechanical properties of sclera.The main conclusions as follows: Under high intraocular pressure,the relative stiffness of the sclera in different regions was the same as that under the normal ocular pressure: anterior sclera region > equatorial sclera > posterior sclera.The stiffness of the sclera in the same area increased with the increase of intraocular pressure As the intraocular pressure increased,the maximum load in the same region of sclera decreased,indicating that the sclera of patients with high intraocular pressure were more vulnerable.3.Spectrophotometry and Sirius red staining-polarization imaging were used to analyze the collagen content and structure in sclera of different regions,and to explore the relationship between the collagen content and scleral mechanical properties.The results showed that the collagen content in different regions of sclera was: posterior sclera > equatorial sclera > anterior sclera.Although the total collagen content in the anterior sclera was lower,the type I collagen content was higher than that in equatorial and posterior sclera.Besides,the collagen fibers in anterior sclera composed of larger fiber bundles with long straight shapes and relatively regular arrangement.The posterior sclera mainly consisted of type III collagen,and the collagen fibers were thin,curly,and disorderly arranged.It indicated that the different mechanical properties of different sclera regions were mainly related to the diverse type and structure of collagen in different regions of sclera.