The micro-structure and biomechanics of eyelid tarsus

Eyelid tarsus is a fibrocartilagenous extracellular matrix around meibomian glands providing structural support to eyelids and play important roles in the integrity of the ocular surface. There are no previous studies investigating the relationship between micro-structure and function of eyelid tarsus. To investigate the structure of extracellular matrix and the biomechanical properties of tarsus, rabbit tarsus were stained with hematoxylin and eosin (H&E), MASSON and Verhoeff's Van Gieson (EVG), distribution of collagen and elastin fibers in tarsus extracellular matrix were analyzed with scanning electron microscopy. Tarsus strips were collected and went through uniaxial tensile test with an Instron Universal Testing Machine. Data from 15 tarsus samples were included in the study. The initial tensile modulus was 2.554 ± 1.453 Mpa, and the final tensile modulus was 23.554 ± 3.657 Mpa, with an extensibility of 35.47 ± 7.46%. Collagen fibers formed peripheral layers of lamellae around meibomian glands, while the elastin fibres were organized in a parallel arrangement in horizontal and sagittal section, and in a crossed arrangement around meibomian glands. After tensile test, elastin fibres were stretched and arranged perpendicular to the direction of the collagen fibril lamellae. The findings of this study suggest that the extracellular matrix structure formed by collagen-elastin network contributes to a nonlinear mechanical characteristic of eyelid tarsus.