Structural properties of human scleral tissues are investigated using polarization-dependent terahertz time-domain spectroscopy. Cross-linked tissue shows polarization-independent transmission properties, whereas normal tissue is polarization-dependent. This results from the different structural arrangements of the collagen fibrils that compose the human scleral tissues. In cross-linked tissue, collagen fibrils structurally form interlocking arrangements, unlike the regular parallel arrangement found in normal tissue. Our results demonstrate that terahertz spectroscopy is a powerful tool for investigating the structural characteristics of biological tissues and systems. (C) 2015 Elsevier B.V. All rights reserved.