Abstract
Purpose :
Modulating the mechanical properties of lamina cribrosa (LC) or sclera has been proposed for reducing sensitivity to elevated IOP and thus susceptibility to glaucoma damage. Due to the complexity of the region numerical techniques are necessary to predict the effects of tissue changes and design optimal interventions. While it is well known that the collagen fibers of the LC and sclera bear the forces of IOP, how the fibers transmit the forces remains unclear. We hypothesized that the effects of tissue modulation will depend heavily on whether the collagen fibers of the LC and sclera transmit forces over long distances or if they transfer them to other fibers and dissipate them in the immediate vicinity.
Methods :
A section through the LC of a sheep eye was imaged using polarized light microscopy to reveal the collagen density and fibers. Based on this image, two specimen-specific computational models were built representing extremes of the fiber behavior: a highly dissipative conventional continuum model (CC) where the fibers and forces are “smeared” within the elements and their boundaries; and a novel direct fiber model (DF) where the fibers act independently and carry forces over long distances (Fig 1). Both models were used to simulate a canal expansion of 10%. Regions of the LC and sclera were selected for stiffening or softening.
Results :
Modulating tissue properties had significant effects on the response of the whole region (Fig 2). The force dissipation process had large effects on the effects of the modulation. In the dissipative CC models, the changes were confined primarily within the area where tissue properties changed, with changes in the LC spreading farther than those in the sclera. In the DF models, the largest differences were also localized to the place of change, but some substantial differences extended far from the change.
Conclusions :
The collagen fibers of the LC and sclera form complex interweaving bundles spanning mm-scale distances in the optic nerve head. Our modeling results indicate that accurately predicting how LC and sclera respond to tissue modulation requires a more detailed understanding of how fibers transmit the forces in actual tissues.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.