Another consequential factor
Another potentially important factor is optic nerve tension. Investigators who recently used a numerical model to look at the effect of tension in the optic nerve sheath on the ONH found, surprisingly, that traction forces in the optic nerve sheath were great and created stress in the peripapillary tissue nasally and temporally (Wang et al. Invest Ophthalmol Vis Sci 2016;57:2452-2462. doi: 10.1167/iovs.15-18986).
When those investigators then looked at the effects in a small clinical cohort using optical coherence tomography, they also surprisingly found large strains in the lamina cribosa. With ocular movements, specifically adduction, strains in the lamina cribosa were found to be “quite significant,” according to Dr. Ethier.
The observed strains were comparable to the strains seen due to IOP increases (Wang et al. Invest Ophthalmol Vis Sci 2016;57: 5825-5833. doi:10.1167/iovs.16-20560).
The same investigators also identified that the optic nerve sheath is tighter with greater tension in patients with glaucoma. Dr. Ethier noted that the clinical relevance of this is not yet clear, but he believes it is necessary to consider more than just IOP when thinking about glaucoma.