The Roles of Cornea and Axial Length in Corneal Hysteresis among Emmetropes and High Myopes: A Pilot Study

Abstract

Purpose: To observe the roles of cornea and axial length (AL) in corneal hysteresis (CH) among emmetropes and high myopes.Materials and Methods: The CH, corneal resistance factor (CRF) and corneal-compensated intraocular pressure (IOPcc) of 40 young emmetropes (spherical equivalent +/−0.50 D) and 40 age-matched high myopes (−6D or more) were measured by the Ocular Response Analyzer. AL was measured using a partial coherence interferometer. The mean keratometry reading (meanK) and corneal volume (CV) in 4 zones were measured using the Pentacam. Full stromal thickness (FST) and epithelial and Bowman's thicknesses (Epi + BT) were evaluated using confocal microscopy. Valid confocal microscopic results from the more emmetropic eyes of 30 emmetropes and the more myopic eyes of 27 high myopes were studied.Results: High myopes exhibited significantly longer AL (27.34 ± 0.90 mm versus 23.71 ± 0.79 mm), lower CH (10.17 ± 1.38 mmHg versus 11.11 ± 1.25 mmHg), and higher IOPcc (16.50 ± 3.05 mmHg versus 13.91 ± 2.49 mmHg) compared with emmetropes. The 2 groups showed similar CRF, CVs, meanK, FST and Epi + BT. By combining the results of both groups, CH and CRF were significantly correlated with FST (r2 = 0.368 and r2 = 0.408, respectively), CVs (r2 = 0.251–0.391 and r2 = 0.201–0.346, respectively), but not with Epi + BT or meanK. Furthermore, AL and IOPcc were significantly correlated with CH (r2 = 0.112 and r2 = 0.161, respectively) but not with CRF. The multivariate analysis indicated that FST (standardized coefficients, β = 0.591) and CV (β = 0.575) had stronger association than IOPcc and AL for CH.Conclusions: High myopes exhibited lower CH than emmetropes. Although CH had stronger correlation with FST than AL, it might contain the biomechanical properties of components other than the cornea.