We propose here a conceptual framework for understanding the optic nerve head (ONH) as a biomechanical structure. Basic principles of biomechanical engineering are used to propose a central role for intraocular pressure (IOP)-related stress and strain in the physiology of ONH aging and the pathophysiology of glaucomatous damage. Our paradigm suggests that IOP-related stress and strain (1) are substantial within the load-bearing connective tissues of the ONH even at low levels of IOP and (2) underlie both ONH aging and the two central pathophysiologies of glaucomatous damage - mechanical failure of the connective tissues of the lamina cribrosa, scleral canal wall, and peripapillary sclera, and axonal compromise within the lamina cribrosa by a variety of mechanisms. Modeling the ONH as a biomechanical structure generates a group of testable hypotheses regarding the central mechanisms of glaucomatous damage and provides a logic for classifying the principal components of the susceptibility of an individual ONH to a given level of IOP. © 2004 Elsevier Ltd. All rights reserved.