Outline

• Basic Concepts
• IOP-related Stress and Strain are high in the ONH
• IOP-related axon loss is multi-factorial
• IOP-related connective tissue damage is multi-factorial
• 'Glaucomatous' is an appearance (not an etiology)
• The larger concept of IOP-related Optic Neuropathies
  - Glaucomatous and 'Non-glaucomatous'
• How some non-IOP-related processes look 'glaucomatous

Summary

Burgoyne and colleagues have introduced the first digital 3D reconstructions of the normal and early glaucoma monkey ONH connective tissues which demonstrate that at the earliest stage of glaucomatous damage the connective tissues of the lamina cribrosa and neural canal wall are profoundly and permanently damaged. This damage should make the ONH more susceptible to further damage at the same or even lower levels of IOP. Finite element models based on 3D reconstructions such as these will allow IOP-related stress and strain within each portion of the connective tissue architecture to be estimated. Such modeling will open the door to testing a series of hypotheses that are central to a Biomechanical view of this neuropathy. These include:

1. IOP-related connective tissue stress and strain are high at normal levels of IOP;
2. Regardless of the IOP at which they occur, IOP-related connective tissue stress and strain govern the two central pathophysiologies of the 'glaucomatous' optic neuropathies:
   1. IOP-related axonal damage which is multifactorial (compressive, ischemic, glial cell mediated, and more�),
   2. IOP-related connective tissue damage - otherwise known as mechanical failure - the predictable pattern of which is unique to each individual ONH and centrally underlies the clinical phenomenon of glaucomatous cupping.

*Figure originates from the paper 'Digital Three-Dimensional Reconstruction of the Normal and Early-Glaucoma Monkey Optic Nerve Head Connective Tissue', by Claude F. Burgoyne, J. Crawford Downs, Anthony J. Bellezza and Richard Hart, which will appear in the December issue of IOVS. Reprinted with permission of the publisher. The ONH as a Biomechanical Structure appears as an article in the next issue of Progressive Retinal and Eye Research.

Issue 6-2

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