Mechanical Factor Analysis on the Sclera: Changes of Scleral Mechanical Properties in the Process of Emmetropization and Myopization and the Effects of Mechanical Stimulation on Scleral Remodeling

Abstract

To increase the understanding of mechanical factors as related to scleral remodeling in the process of emmetropization and myopization. An eyelid suture that lasted 60 days was performed on one-month-old rabbits to establish an experimental monocular visual deprivation myopia model and the axial length was recorded. HE staining and transmission electron microscope were used to observe the scleral structure. The Instron 5544 was used to measure scleral elastic modulus after measuring the scleral thickness. The scleral fibroblasts were isolated and were cultured under mechanical stimulation using the FX-4000 system. The collagen expression and collagen I α1, MMP-2, and TIMP-2 mRNA expression were detected. During regular emmetropization, the scleral collagen synthesis was higher than decomposition and the diameter of collagen fibrils increased, and then the sclera thickened and mechanical properties improved. During myopization, the scleral collagen decomposition was higher than synthesis and the diameter of collagen fibrils was smaller, and then the sclera thinner and mechanical properties lower, which resulted in a difference in scleral tissue strain. The proper (smaller) mechanical stimulation could improve the collagen synthesis and reduce the decomposition. However, the larger mechanical stimulation could reduce the collagen synthesis and enhance the decomposition. The results suggested that the scleral structure, collagen metabolism, and mechanical properties changed in the process of emmetropization and myopization, and mechanical stimulation affected the scleral remodeling. In addition, the changes in mechanical factors were an important cause of scleral growth, axial elongation, and even myopization. Funding Statement: This study was supported by the National Natural Science Foundation of China (11802209), the Natural Science Foundation of Shandong Province China (ZR2019MA005). Declaration of Interests: The authors have no proprietary interest in any of the materials discussed in this article. Ethics Approval Statement: The experimental protocols were approved by the Animal Care and Protection Committee of Weifang Medical University. We confirm that all experiments were performed in accordance with relevant guidelines and regulations.