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Joel Palko, Benjamin Cruz Perez, Jun Liu; Regions of increased strains in the human peripapillary sclera with histologic correspondence to the arterial circle of Zinn-Haller. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6146.
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To evaluate the inflation strains in the peripapillary human sclera and compare the strain patterns to histology.
Following preconditioning, five human scleral shells were inflated from 10 mmHg to 11.5, 13, 15 and 19 mmHg. A volume of 9 mm x 7.5 mm encompassing the full-thickness of the nasal side of the peripapillary sclera was scanned at each pressure using a 55-MHz ultrasound probe by stacking 2D scans at 20 μm intervals. 3D speckle tracking was performed in the volume using a cross-correlation algorithm (Tang & Liu, J Biomech Eng 2012, 134(9)). Full strain tensors and principal strains were calculated at each tracking point. One specimen was then fixed in 10% formaldehyde and sections of the optic nerve head (ONH) were obtained with Mason’s Trichrome staining from posterior to anterior beginning at the scleral surface.
Regions of significantly increased strains were frequently observed in the human peripapillary sclera. The first principal strains (mostly meridional tension) and the third principal strains (mostly radial compression) demonstrated a circular region with increased strain magnitudes surrounding the scleral canal approximately 300-400 μm into the thickness of the peripapillary sclera. The first principal strains at 0, 200 and 400 μm depth from one eye are shown in Fig. 1. These regions had a strain roughly an order of magnitude greater than the surrounding tissue and were not present on the scleral outer surface. The histology of this eye at a similar depth showed correspondence of these regions of increased strains with the location of the arterial circle of Zinn-Haller (Fig. 2).
This is the first report of large strains in local areas of the peripapillary sclera corresponding to the arterial circle of Zinn-Haller on histology. The increased strains may represent compression and distortion of these vessels during IOP elevation. Previous studies have shown associations with ischemia to these arteries and glaucomatous damage, as it is the main blood supply to the lamina cribrosa (Hiraoka et al., Br J Ophthalm 2012 96(4)). Preliminary computational models suggested that scleral biomechanical properties could have a strong influence on the strains in these vessels. Future studies will investigate interactions of scleral biomechanics and blood supply to the ONH.
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