Mechanical Environment of the Optic Nerve Head in Glaucoma

Abstract

The optic nerve head (ONH) is of particular interest from a biomechanical perspective because it is a weak spot within an otherwise strong corneo-scleral envelope. The lamina cribrosa provides structural and functional support to the retinal ganglion cell axons as they pass from the relatively high-pressure environment in the eye to a low-pressure region in the retrobulbar cerebrospinal space. To protect the retinal ganglion cell axons within this unique environment, the lamina cribrosa in higher primates has developed into a complex structure composed of a three-dimensional network of flexible beams of connective tissue. The ONH is nourished by the short posterior ciliary arteries, which penetrate the immediate peripapillary sclera to feed capillaries contained within the laminar beams. This intrascleral and intralaminar vasculature is unique in that it is encased in load-bearing connective tissue, either within the scleral wall adjacent to the lamina cribrosa, or within the laminar beams themselves. Glaucoma is a multifactorial disease, and we believe that biomechanics not only determines the mechanical environment in the ONH, but also mediates IOP-related reductions in blood flow and cellular responses through various pathways. Our current understanding of the mechanical environment of the ONH is described, with particular emphasis on the influence of biomechanics in glaucoma.

Radiation treatment inhibits monocyte entry into the optic nerve head and prevents neuronal damage in a mouse model of glaucoma

“…Much of the field has focused on astrocytes, microglia, and RGCs themselves, with some interest in the endothelial control of blood flow (65)(66)(67). Our demonstration that specific radiation of the eye can prevent glaucoma is an important finding.…”

Optical Coherence Tomography of the Swollen Optic Nerve Head: Deformation of the Peripapillary Retinal Pigment Epithelium Layer in Papilledema

“…Although the proximate cause of early edema is stagnant axonal transport, there still remains some uncertainty about the relative effects of compression and ischemia. [1][2][3] Burgoyne et al 4 and others [5][6][7][8][9][10][11] have proposed a conceptual approach that analyzes the optic nerve head (ONH) as a biomechanical structure. They hypothesize that stress (force/ cross-sectional area) and strain (local deformation) on the ONH may be key determinants of axonal, glial, and vascular dysfunction in the pathogenesis and progression of glaucoma.…”

Pressure balance and imbalance in the optic nerve chamber: The Beijing Intracranial and Intraocular Pressure (iCOP) Study

“…This implies that if the TOPG increases from the center to the periphery, the fiber bundles of the optic nerve will be compressed. It has been shown that the optic nerve is particularly susceptible to pressure changes and prone to deformation (Crawford Downs et al, 2011;Downs et al, 2008;Sigal et al, 2007). Even though these studies focused on the lamina cribrosa and the scleral canal, it is reasonable to assume that the optic canal is stiffer than the scleral canal.…”