The elastic modulus and collagen of sclera increase during the early growth process

The aim of this study was to investigate the changes in the elastic modulus and collagen in scleral tissues of different ages. The eyeballs of 1-, 2- and 3-month-old New Zealand white rabbits were obtained to assess three regions of the sclera-anterior, equatorial and posterior. The three regions of the scleral tissues were then separately divided into four groups. The first group was made into scleral strips for elastic modulus measurement using an Instron 5544. The second group was HE stained for observation of the scleral structures. The third group was used for electron microscopy to observe the size distribution of collagen fibrils. The last group was homogenized and the concentration of hydroxyproline was measured to determine the collagen content. The elastic modulus and diameters of the collagen fibrils of each scleral region increased with age, while the number of scleral fibroblasts decreased. The posterior sclera had a looser collagen fibrils arrangement, less collagen and a lower elastic modulus than the anterior and equatorial sclera. The structure across the scleral regions changed constantly, and the diameter of the scleral collagen fibrils increased during the early growth process, which led to the improvement of the elastic modulus of the scleral tissues. The posterior sclera had a looser collagen fibril arrangement, less collagen and lower elastic modulus than the anterior and equatorial sclera; this finding may explain several physiological and pathological uncertainties of the sclera, such as emmetropization, posterior sclera expanding and myopia.