April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Experimental characterization of the nonlinear displacements and deformations of human lamina cribrosa (LC) microstructure during acute increases in IOP
Author Affiliations & Notes
  • Jonathan L Grimm
    UPMC Eye Ctr/Eye and Ear Inst/Ophthal, University of Pittsburgh, Pittsburgh, PA
  • Ning-Jiun Jan
    UPMC Eye Ctr/Eye and Ear Inst/Ophthal, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
  • Donald J Brown
    Gavin Herbert Eye Institute, University of California, Irvine, CA
  • Ian A Sigal
    UPMC Eye Ctr/Eye and Ear Inst/Ophthal, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 4254. doi:
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    • Get Citation

      Jonathan L Grimm, Ning-Jiun Jan, Donald J Brown, Ian A Sigal; Experimental characterization of the nonlinear displacements and deformations of human lamina cribrosa (LC) microstructure during acute increases in IOP. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4254.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

To measure eye-specific displacements and deformations of the human LC microstructure during acute increases in IOP and test the hypothesis that the biomechanical effects of IOP are nonlinear.

 
Methods
 

Six human eyes from four donors aged 23 to 82 were scanned using second harmonic generated imaging (Zeiss 510 Meta LSM, 1.76 to 4.96 µm/pixel lateral resolution, 2 µm depth resolution) at various levels of IOP between 10 and 50 mmHg (3 pressure steps for 5 eyes and 7 pressure steps for 1 eye). After an IOP change the eyes were allowed to equilibrate for 30 min before imaging. An image registration technique [Sigal et al. IOVS In-Press] was used to find the deformation mapping between maximum intensity projection images at different levels of IOP. The mappings were analyzed to determine the magnitude and distribution of the IOP-induced displacements and deformations. A linear regression was fit to predict the deformations per mmHg as a function of the pressure allowing for box-cox transformations.

 
Results
 

For Eye 1 the median LC deformation magnitudes were 0.41, 0.25, 0.17, 0.22, 0.10 and 0.12 μm/mmHg, respectively for pressure differences 10-15, 10-20, 10-35, 10-30, 10-35, and 10-40 mmHg (Figure 1). The other eyes showed a similar pattern of decreasing deformation per mmHg as IOP increases. Deformation per mmHg decreased significantly as IOP change increased (p<0.001, R2=.95).

 
Conclusions
 

Previously we reported substantial effects on the LC of acute increases in IOP (10 to 50 mmHg). Here we found ~55% of the effects of IOP between 10 and 20 mmHg, and ~45% between 20-40 mmHg (twice the IOP increase), denoting substantial nonlinearity in LC mechanics. The roles of LC and sclera properties on this nonlinearity remain to be determined. To the best of our knowledge, these are the first measurements of nonlinear LC microstructure response to IOP.

 
 
Figure 1. Displacement magnitudes per mmHg of IOP elevation plotted by pressure step. Notice that the nonlinear decrease. The vessel deformed more than the surrounding tissue, probably due to lack blood pressure. The vessel displacements were excluded from other results.
 
Figure 1. Displacement magnitudes per mmHg of IOP elevation plotted by pressure step. Notice that the nonlinear decrease. The vessel deformed more than the surrounding tissue, probably due to lack blood pressure. The vessel displacements were excluded from other results.
 
Keywords: 577 lamina cribrosa • 549 image processing • 568 intraocular pressure  
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