April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Stiffness of the Trabecular Meshwork In Living Eyes
Author Affiliations & Notes
  • Larry Kagemann
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
  • Mark Johnson
    Departments of Biomedical Engineering, Mechanical Engineering and Ophthalmology, Northwestern University, Evanston, IL
  • Bo Wang
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
  • Gadi Wollstein
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
  • Hiroshi Ishikawa
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
  • Zach Nadler
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
  • Ian A Sigal
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
  • Yun Ling
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA
  • Richard Anthony Bilonick
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA
  • Joel S Schuman
    UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA
    Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
  • Footnotes
    Commercial Relationships Larry Kagemann, None; Mark Johnson, Acucela (P); Bo Wang, None; Gadi Wollstein, None; Hiroshi Ishikawa, None; Zach Nadler, None; Ian Sigal, None; Yun Ling, None; Richard Bilonick, None; Joel Schuman, Zeiss (P)
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 2170. doi:
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    • Get Citation

      Larry Kagemann, Mark Johnson, Bo Wang, Gadi Wollstein, Hiroshi Ishikawa, Zach Nadler, Ian A Sigal, Yun Ling, Richard Anthony Bilonick, Joel S Schuman; Stiffness of the Trabecular Meshwork In Living Eyes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2170.

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

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Abstract
 
Purpose
 

Trabecular meshwork (TM) stiffness has been shown to be elevated in cadaveric glaucomatous eyes (mean 80.8, range 0.5-565 kPa) compared with normal eyes (4.0, 0.5-10kPa) [Last et al, IOVS 2011(52)5:2147-2152]. However; those measurements were made in isolated tissues by atomic force microscopy. In-vivo, the TM is suspended in tension between the posterior cornea and ciliary body. Ciliary muscle activity may increase the effective stiffness of the TM. We examined this hypothesis in living eyes, comparing the effect of IOP on outflow pathway morphology with previous measurements made in cadaveric eyes.

 
Methods
 

The temporal limbus of 33 eyes of 19 healthy subjects (12 male, 7 female, age 40 ± 15 years) was imaged by spectral-domain optical coherence tomography (Cirrus HD-OCT, Zeiss, USA) at baseline and during IOP elevation (ophthalmodynamometer applied at 30 Grms force). IOP was measured at baseline and during IOP elevation by Goldmann applanation tonometry. Vascular landmarks were used to identify corresponding locations in baseline and IOP elevation scan volumes. Schlemm's canal cross-sectional area (SC-CSA), mean inner to outer wall distance (IOD) and mean TM thickness (TMt), the distance from the anterior chamber to SC inner wall, were measured at 5 locations within a 1 mm length of SC using ImageJ as described previously [IOVS 2010; 51(8): 4054-4059]. Data were compared with measurements by VanBuskirk et al in cadaveric eyes (IOVS, 1982;22(5):625-32, Table).

 
Results
 

A mean increase in IOP of 23 mmHg (Table) led to a decrease of SC-CSA (39%) and IOD (18%) while TMt was not unchanged (Table). In cadaveric eyes, the decreases in SC-CSA were greater than in live eyes (Table), but the TMt was also insensitive to IOP elevation.

 
Conclusions
 

The collapse of Schlemm's canal with increasing IOP while TM thickness changed little suggests that the TM acts as a membrane under tension. This was true both in live and cadaveric eyes. However, the 39% decrease in SC-CSA and IOD with increasing IOP in living eyes, was smaller than the decrease observed in cadaveric eyes. This suggests that the tension and thus, the effective stiffness of this membrane may be greater in live eyes, presumably due to ciliary muscle contraction. The contribution of the TM in preventing collapse of the SC may differ in living versus cadaveric eyes.

  
Keywords: 735 trabecular meshwork • 550 imaging/image analysis: clinical  
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