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Editors Selection IGR 19-4

Anatomical Structures: Peripapillary collagen fiber disposition and glaucoma

Comment by Crawford Downs on:

50955 Quantitative mapping of collagen fiber orientation in non-glaucoma and glaucoma posterior human sclerae, Pijanka JK; Coudrillier B; Ziegler K et al., Investigative Ophthalmology and Visual Science, 2012; 53: 5258-5270

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Optic nerve head (ONH) biomechanics likely plays an important role in the development and progression of glaucoma, but it is not well understood. Experimental and numerical studies indicate that the peripapillary sclera is influential in determining ONH biomechanics, as this ring of sclera defines the mechanical boundary condition for the contained lamina cribrosa. Pijanka, Boote and colleagues used a quantitative X-ray scattering technique (WAXS) to characterize collagen fibril anisotropy (orientation and degree of directionality) in posterior scleral shells from ostensibly normal (n = 7) and glaucomatous (n = 5) human donor eyes. Results show there is a highly aligned circumferential ring of collagen surrounding the ONH, but much less directionality in the mid-posterior sclera. This had been reported in previous histologic and numerical studies, but had never been measured directly. There was a small but statistically significant difference in peripapillary scleral anisotropy between the normal and glaucomatous eyes, but this was dwarfed by the regional differences within eyes. The most important result is that the degree of circumferential alignment in the peripapillary sclera varied greatly around the ONH, with the superonasal quadrant showing much less circumferential orientation of collagen than the other quadrants. This result suggests that while the circumpapillary ring of collagen generally shields the ONH from excessive IOP-related strain, there may be regions where peripapillary scleral strain is much higher than other regions, which could result in focal strain concentrations in the adjacent peripheral lamina cribrosa.

Local peripapillary scleral biomechanics may play a role in disease onset and progression

Glaucoma is frequently associated with focal axonal damage in the peripheral ONH, so this finding bolsters the notion that the local peripapillary scleral biomechanics may play a role in disease onset and progression. The direct link between scleral biomechanics and axonal damage has yet to be established however, so these associations remain speculative.

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