Determining The Corneal Biomechanical Properties Of Porcine With Eye Globe Infation Tests

The cornea is one kind of biological soft tissue material,which occupies an important position in the eye refractive system,its biomechanical properties can maintain the corneal's basis morphology,once the corneal biomechanical performance changed,it will affect overall refractive power of the eye.At the same time,the biomechanical properties of the cornea have an important reference value for the diagnosis and treatment of corneal diseases,such as keratoconus and corneal trauma,and also have an important reference value for the design of refractive surgery and the design of corneal contact lens.Because of the cornea's biomechanical properties have the special significance to the cornea,the researchers need to measure the biomechanical properties of the cornea more accurately and establish a precise corneal simulation model.In this dissertation,porcine cornea as the research object for studying the mechanical properties through the inflation tests and finite element simulation.1.The main research work:(1)Build an inflation test system for corneas and improve the method for the inflation test of eye globe that could eliminate the displacement effect of sclera to cornea during the test.Respectively,two kinds of measurements for cornea were made ex vivo,one was the inflation test of cornea,and the other was the inflation test of eye globe,from the test we obtained the relationship between corneal apex displacement-intraocular pressure in each test.Then,based on shell theory and according to the relationship between corneal apex displacement-intraocular pressure,we could calculate the corneal elastic modulus and corneal strain,so we obtained the stress-strain curves of each cornea.At last,the mechanical properties of the cornea were compared and analyzed which obtained in the two groups in elastic phase.(2)Established a finite element model which considered collagen fiber distribution in the cornea based on the microstructure of cornea for the inflation test of eye globe.The lamellar structure of porcine cornea was observed by scanning electron microscopy and analyzed the main elements in the cornea.In ABAQUS software,we selected Holzapfel constitutive model which match the corneal structure to calculate the mechanical properties of the cornea.Adjusted the parameters of Holzapfel constitutive model reasonably which were reported in the reference and simulated the relationship between corneal apex displacement-intraocular pressure in the inflation test of eye globe.So the Holzapfel constitutive model parameters for the inflation tests of eye globe were obtained in the intraocular pressure with15.28-30.17 mmHg.The mechanical properties of the porcine cornea were simulated by different intraocular pressure,and discussed how the 3 main parameters in the Holzapfel constitutive model effected on the mechanical properties of the cornea when changed them.2.The main conclusion:(1)The results of the two inflation test showed that the elastic modulus obtained by the inflation test of eye globe was smaller than that of the corneal inflation test.The strain obtained by the inflation test of eye globe was bigger than that of the corneal inflation test in the intraocular pressure with 15.28-30.17 mmHg.(2)The lamellar structure of corneal section parallel to each other which were observed by scanning electron microscopy;By transmission electron scanning electron were observed,at 0 mmHg,the fibers are curved,At 30 mmHg,the fibers were stretched and partially broken.(3)The results of the simulation calculation showed that in the intraocular pressure with 15.28-30.17 mmHg,the higher the intraocular pressure,the greater the stress and displacement of the cornea,but less on the distribution of stress and displacement.(4)The effects of three main parameters on the mechanical properties of the corneas were calculated.Preferential orientations are the superior-inferior(SI)and the nasal-temporal(NT)meridians,we emphatically analyzed the influences of the different dispersion degreea(?)long the preferential orientations on the stress distribution and displacement distribution,the ?affected the distribution of stress in the cornea,but does not affected the direction of the distribution of corneal displacement.When the corneal intraocular pressure was the same,the greater the degree of fiber dispersion,the more uniform stress distribution of the cornea,corneal apical displacement was smaller.The above,we obtained the mechanical properties of the corneal elastic phase through the inflation test of eye globe,observated the cornea structure and the main chemical elements and established the finite element model with the microstructure of the cornea,for providing theoretical basis and technical guidance for the treatment and operation of clinical corneal disease.