Quantitative Analysis of Corneal Energy Dissipation and Corneal and Orbital Deformation in Response to an Air-Pulse in Healthy Eyes

Abstract

Citation: Vellara HR, Ali NQ, Gokul A, Turuwhenua J, Patel DV, McGhee CNJ. Quantitative analysis of corneal energy dissipation and corneal and orbital deformation in response to an airpulse in healthy eyes. Invest Ophthalmol Vis Sci. 2015;56:6941-6947. DOI:10.1167/iovs.15-17396 PURPOSE. To examine and evaluate ocular biomechanical metrics and additionally derived corneal and orbital components using a noncontact Scheimpflug-based tonometer (CorVis ST) in a population of healthy eyes. METHODS.A total of 152 eyes of 152 participants were examined by slit-lamp biomicroscopy, corneal tomography, and the CorVis ST (CST). This determined the distribution of outputs from the CST, such as deformation amplitude (DA), and additionally derived parameters, including maximum corneal deformation (MCD), maximum orbital deformation (MOD), and corneal energy dissipation (CED).RESULTS. The mean age of participants was 35.88 6 13.8 years. Deformation amplitude significantly correlated with age (r ¼ 0.24, P ¼ 0.002) but not sex or ethnicity (P > 0.05). Multiple linear regression analysis revealed significant correlations between DA and age (r ¼ 0.19, P ¼ 0.006) and DA and IOP (r ¼ À0.59, P < 0.001). Age correlated with MCD (r ¼ 0.20, P ¼ 0.01), MOD (r ¼ 0.18, P ¼ 0.03), and CED (r ¼ 0.39, P < 0.001). Males had a lower MOD than females (0.24 vs. 0.26 mm, respectively, P ¼ 0.01); however, there were no differences in MCD or CED between sexes (P > 0.05). There were no significant differences between ethnicities for MCD, MOD, and CED (P > 0.05). Multiple linear regression analysis revealed significant correlations between MCD and IOP (r ¼ À0.65, P < 0.001), CED and age (r ¼ 0.41, P < 0.001), CED and IOP (r ¼ 0.28, P ¼ 0.001), and between CED and central corneal thickness (CCT) (r ¼ À0.36, P < 0.001).CONCLUSIONS. The isolation of the corneal component (MCD) should be used when analyzing deformation characteristics in diseases that only affect the cornea. This study establishes a baseline for a population of healthy eyes. Future publications will identify differences in MCD, MOD, and CED between healthy and diseased populations.

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“…There is a weak positive correlation between MOD and age in healthy subjects (r=0.18, p=0.03) 7. Therefore, adjusting for the lower age in the healthy participants would further increase the difference in MOD between groups.…”

“…However, only a few parameters from the CST have been shown to be repeatable. These include deformation amplitude (DA), first applanation time, MOD and MCD 7 12…”

“…The videos were processed using methods previously described by Koprowski8 and Vellara et al 7. Video analysis included the use of the Canny edge detection, morphological image processing (close operation) and corneal contour.…”

“…Video analysis included the use of the Canny edge detection, morphological image processing (close operation) and corneal contour. The visible corneal contour at the edges of the video allows derivation of an orbital deformation response and this has been explained in detail by the authors in an earlier publication 7. The overall change in orbital position over the course of the video is termed the maximum orbital deformation (MOD) 7…”

“…The in vivo ocular response to the air pulse was noted to include a corneal response and a collateral orbital response 6. Investigators have since developed algorithms to derive the pure orbital response and described its distribution in the normal population 7 8. The advantages of this technique over previous methods include the rapid examination time and commercial availability of the device, and ocular anaesthesia is not required.…”