A Novel and Simple Method to Assess Corneal Biomechanics Using Schiotz Tonometer

Abstract

Background: The present study introduces a novel method to evaluate corneal biomechanics, which has a key role in diagnosing keratoconus (KC) or keratectasia (KE). Methods: In this multicentre, prospective, single-blind study, patients with myopia, cataracts, or KC underwent corneal biomechanics evaluation with a Schiotz tonometer, before and after corneal crosslinking (CXL) or Femtosecond assisted laser in situ keratomileusis (FS-LASIK). The corneal biomechanics metric (Mulee factor, MF) was calculated from the data obtained with the tonometer. Clinical significance was verified by analysis of the correlation of MF and ocular morphology metrics and efficiency of MF in predicting the occurrence of KC or KE. Findings: A negative relation was found between the MF and Young’s modulus (P<0·001) and MF and maximal stress (P<0·001) in an in vitro study on rabbit eyeballs. MF in normal eyes (myopia and cataract eyes) was 2·890·43. MF before FS-LASIK was 2·940·35, increasing to 3·710·42 one month after FS-LASIK (P<0·001). In the normal population, pre-operative MF was negatively correlated with age (P<0·001), positively correlated with central corneal thickness (P=0·03), but not related to anterior chamber depth, ocular axis length, intraocular pressure, cornea diameter, and cornea curvature. MF was 4·090·56, decreasing to 2·140·55 one month after CXL. MF was 3·360·51 in eyes with forme fruste keratoconus (FFKC). There were 3, 6, and 10 cases of KC or KE after FS-LASIK, CXL, or FFKC, respectively. The cut-off points for predicting KC or KE with MFs were 4·67, 2·67, and 3·5 in patients with FS-LASIK, KC, and FFKC (P<0·01, P<0·01, and P<0·01, respectively). Interpretation: The MF can sensitively reflect corneal biomechanics and is not influenced by ocular metrics. The MF predicts KC and KE with high specificity and sensitivity. Funding Statement: This study was supported by the Natural Science Foundation of Shandong Province (2009GQ10002037). Declaration of Interests: There are no conflicts of interest to declare. Ethics Approval Statement: Animals used in this study were treated in accordance with Shandong Provincial Hospital affiliated to Shandong University Animal Experimentation Ethic Committee (AEEC) guidelines, and were approved by the AEEC.