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Jun Liu, Elias Pavlatos, Keyton Clayson, Xueliang Pan; Influence of physiological parameters on human corneal displacements in response to ocular pulse. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1396.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the influence of baseline intraocular pressure (IOP), ocular pulse amplitude (OPA), and heart rate (HR) on corneal deformation during ocular pulse cycles in human donor eyes.
Human donor globes (n=10) were tested within 72 hours post-mortem. Whole globes were immersed in 3.5% Poloxamer 188 at 4oC for 18 hours to deswell the cornea before testing. Oscillatory IOP changes were produced using an infusion pump to simulate the ocular pulse, and ultrasound scans of the central 5.7 mm of cornea in the nasal-temporal direction were obtained using a 50 MHz transducer (Vevo 2100, VisualSonics). In each eye, the nominal condition was set to a baseline IOP=15 mmHg, OPA=3 mmHg, and HR=72 beats per minute (BPM). Each parameter was then varied separately to a baseline=10 or 20 mmHg, OPA=1 or 5 mmHg, and HR=45 or 100 BPM. The nominal condition was repeated after each parameter variation. Ultrasound scans were performed during IOP oscillations under each condition. Corneal displacements were determined using ultrasound speckle tracking (Tang & Liu, J Biomech Eng 2012, 134(9)). A corneal stiffness index (CSI) was defined using an analytical model incorporating the regression slope of displacement versus IOP change. The CSI for each condition was compared using linear mixed models with repeated measures.
The simulated ocular pulse generated cyclic axial corneal displacements in sync with the IOP change (Fig. 1). The CSIs measured under the repeated nominal condition were 121.3±56.2, 117.4±55.4, 113.9±53.3, and 114.3±52.6, and the first three measurements were not different from the last (all p’s>0.05). Compared to the last nominal CSI (Nom4, Fig. 2), several conditions including baseline IOP=10 or 20 mmHg, OPA=5mmHg, and HR=100BPM had significantly different CSIs (p’s<0.01), but the difference was small compared to the inter-eye variance.
Corneal response to ocular pulse can be reliably measured using high frequency ultrasound in donor eyes. Changes in baseline IOP, OPA, HR showed a statistically significant but small influence on the measured corneal stiffness index. Future in vivo studies may take into consideration these measurable physiological parameters to interpret the CSI outcome.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Fig 1. a. Corneal axial displacement induced by ocular pulse and b. displacement/IOP slope in a representative cornea.
Fig. 2: Average CSI (n=10) under each condition.
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