Long overlooked in the pathophysiology of glaucoma, the choroid may finally be getting its due. A team of researchers from Emory University, working with NASA, suggests that certain characteristics of choroidal anatomy at the optic nerve head (ONH) encourage prelaminar neural tissue deformation under edematous conditions. These findings imply that the choroid may also play an important, but previously unappreciated, role in optic nerve head biomechanics.
The researchers developed two geometric models of ONH composition that approximated the high and low extremes of normal physiologic variation: one with a “blunt” choroidal insertion (136µm thick) as it approaches the ONH and another with a “tapered” choroid (61µm thick), Then, they assessed how choroidal volume changes impact biomechanical strain in the region of the lamina cribrosa under both models. Finally, they performed a sensitivity analysis to understand how variation in ONH pressure, tissue material and choroidal swelling influence peak tissue strains.
The team found that choroidal swelling in the blunt choroidal geometric model had a large impact on the prelaminar neural tissue strains; the magnitude was comparable with that expected to occur due to an intraocular pressure of 30mm Hg. Swelling in the tapered model of choroidal geometry also affected strains, but to a lesser extent.
The study concludes that choroidal swelling in models using blunt choroidal geometry was the most influential on prelaminar neural tissue strains. “Taken together, these findings provide rationale for further study on the choroid’s role in ONH biomechanics and tissue function,” they wrote in the paper. While too soon for clinical use, juxtapapillary choroidal variation may have diagnostic value if these findings are borne out by further research.
|Feola AJ, Nelson ES, Myers J, et al. The impact of choroidal swelling on optic nerve head deformation. Invest Ophthalmol Vis Sci. 2018;59:4172-81.