Measurement of Ocular Compliance Using iPerfusion

• Authors: Joseph M Sherwood, Imperial College London; Elizabeth M Boazak, Georgia Institute of Technology; Andrew J Feola, Georgia Institute of Technology; Kim Parker, Imperial College London; Christopher Ethier, Emory University; Darryl R Overby, Imperial College London
• Journal Title: Frontiers in Bioengineering and Biotechnology
• Volume: Volume 7, Number OCT
• Publisher: Frontiers Media SA | 2019-10-25, Pages 276-276
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.3389/fbioe.2019.00276
• Subjects: Engineering, Biomedical; Health Sciences, Medicine and Surgery
• Keywords: Science & Technology; Life Sciences & Biomedicine; Biotechnology & Applied Microbiology; Multidisciplinary Sciences; Science & Technology - Other Topics; sclera; cornea; ocular rigidity; ocular compliance; glaucoma; OUTFLOW FACILITY; BIOMECHANICS; ELASTICITY; VEGF

Abstract

The pressure-volume relationship of the eye is determined by the biomechanical properties of the corneoscleral shell and is classically characterised 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 (Step Response, 41 [37, 46] vs. Discrete Volume, 42 [37, 48] nl/mmHg; mean [95% CI]), although the Step Response Method yielded tighter confidence bounds on individual eyes. 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, Step Response Method). Measuring OC provides a powerful tool to assess corneoscleral biomechanics in mice and other species.