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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Bioeng. Biotechnol. | doi: 10.3389/fbioe.2019.00276

Measurement of Ocular Compliance Using iPerfusion

 Joseph M. Sherwood1, Elizabeth M. Boazak2, Andrew J. Feola2, 3, Kim Parker1, C R. Ethier2, 4* and  Darryl R. Overby1*
  • 1Department of Bioengineering, Faculty of Engineering, Imperial College London, United Kingdom
  • 2Wallace H. Coulter Department of Biomedical Engineering, College of Engineering, Georgia Institute of Technology, United States
  • 3Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Health Care System, United States
  • 4George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, United States

The pressure-volume relationship of the eye is determined by the biomechanical properties of the corneoscleral shell and is classically characterized by Friedenwald’s coefficient of ocular rigidity or, alternatively, by the ocular compliance (OC), defined as dV/dP. OC is important in any situation where the volume (V) or pressure (P) of the eye is perturbed, as occurs during several physiological and pathological processes. However, accurately measuring OC is challenging, particularly in rodents. We measured OC in 24 untreated enucleated eyes from 12 C57BL/6 mice using the iPerfusion system to apply controlled pressure steps, whilst measuring the time-varying flow rate into the eye. Pressure and flow data were analysed by a “Discrete Volume” (integrating the flow trace) and “Step Response” method (fitting an analytical solution to the pressure trace). OC evaluated at 13 mmHg was similar between the two methods (41 [37, 46] versus 42 [37, 48] nl/mmHg; mean [95% CI]), although the Step Response Method yielded tighter confidence bounds. OC was tightly correlated between contralateral eyes (R2=0.75, p=0.0003). Following treatment with the cross-linking agent genipin, OC decreased by 40 [33, 47]% (p=0.0001; N=6). This method to measure OC provides a powerful tool to assess corneoscleral biomechanics in mice and other species.

Keywords: Sclera, Cornea, Ocular rigidity, Ocular compliance, Glaucoma

Received: 14 Jun 2019; Accepted: 01 Oct 2019.

Copyright: © 2019 Sherwood, Boazak, Feola, Parker, Ethier and Overby. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Prof. C R. Ethier, Wallace H. Coulter Department of Biomedical Engineering, College of Engineering, Georgia Institute of Technology, Atlanta, 30332, Georgia, United States, ross.ethier@bme.gatech.edu
Dr. Darryl R. Overby, Department of Bioengineering, Faculty of Engineering, Imperial College London, London, SW7 2AZ, England, United Kingdom, d.overby@imperial.ac.uk