Purchase this article with an account.
Dan E Midgett, Mary Ellen Pease, Harry A Quigley, Thao D Nguyen; Inflation Test of Human Optic Nerve Head using Digital Volume Correlation. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6145.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
It is hypothesized that the mechanical behavior of the lamina cribrosa (LC) plays an important role in the development glaucomatous optic neuropathy. Previous studies have correlated differences in extracellular matrix structure, morphology, and surface deformations of the LC to glaucoma damage. We have developed an inflation experiment that uses second harmonic generation (SHG) imaging and digital volume correlation (DVC) to measure the three-dimensional (3D) displacements and strains in the LC.
Human eyes (N=4) were obtained within 48 hours post-mortem from a tissue bank: 2 glaucoma (age 96 and 94) and 2 control (age 84 and 81). The episclera and extraocular tissues were removed, the optic nerve cut flush with the sclera, and the eye secured to a holder and pressurized using a PBS solution injected through the anterior chamber. IOP was initially set to 20 mmHg then to 45 mmHg. A Zeiss LSM 710 NLO microscope tuned to 790nm with a short pass 485 filter was used to acquire two duplicate image stacks of the LC structure using SHG at 45, 60, & 75 min after pressure set. The DVC algorithm, developed by Toyjanova et al (Experimental Mechanics, 2014) was used to post-process the SHG image stacks to calculate the 3D displacement field between the two IOP. Baseline error was measured by correlating between duplicate stacks using DVC. Displacements were validated using the estimated motion of landmarks and a virtually applied displacement field.
The posterior displacement over the measured LC volume was 283.12±5.53 um and 296.46±7.62 for the 2 normal eyes, and 177.84±5.36 um and 160.96±6.29 um for the 2 glaucoma eyes. The displacement in plane consisted of a unique rigid-body translation, with small, local stretch. In-plane displacement magnitudes were 91.45±35.28 um and 68.61±9.43 um for the 2 normal eyes, and 48.34±9.10 um and 40.13±24.93 um for the 2 glaucoma eyes. Strain across the thickness of the LC was highly compressive (Fig. 1c). The RMS error between the displacements of landmarks and DVC calculations was 1.60±1.66x0.67±0.65 pixels in the plane and 0.83±0.82 pixels out of the plane.
This study demonstrates that accurate, 3D displacement fields can be obtained from SHG imaging of the LC. This allows for the calculation of the strains, stresses, and mechanical properties of the tissues of the ONH. Preliminary results suggest a stiffer inflation response for the LC of glaucoma eyes.
This PDF is available to Subscribers Only