Abstract
Purpose: To investigate corneal biomechanical response parameters in varying degrees of myopia and their correlation with corneal geometrical parameters and axial length.Methods: In this prospective cross-sectional study, 172 eyes of 172 subjects, the severity degree of myopia was categorized into mild, moderate, severe, and extreme myopia. Cycloplegic refraction, corneal tomography using Pentacam HR, corneal biomechanical assessment using Corvis ST and Ocular Response Analyser (ORA), and ocular biometry using IOLMaster 700 were performed for all subjects. A general linear model was used to compare biomechanical parameters in various degrees of myopia, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered as covariates. Multiple linear regression was used to investigate the relationship between corneal biomechanical parameters with spherical equivalent (SE), axial length (AXL), bIOP, mean keratometry (Mean KR), and CCT.Results: Corneal biomechanical parameters assessed by Corvis ST that showed significant differences among the groups were second applanation length (AL2, p = 0.035), highest concavity radius (HCR, p < 0.001), deformation amplitude (DA, p < 0.001), peak distance (PD, p = 0.022), integrated inverse radius (IR, p < 0.001) and DA ratio (DAR, p = 0.004), while there were no significant differences in the means of pressure-derived parameters of ORA between groups. Multiple regression analysis showed all parameters of Corvis ST have significant relationships with level of myopia (SE, AXL, Mean KR), except AL1 and AL2. Significant biomechanical parameters showed progressive reduction in corneal stiffness with increasing myopia (either with greater negative SE or greater AXL), independent of IOP and CCT. Also, corneal hysteresis (CH) or ability to dissipate energy from the ORA decreased with increasing level of myopia.Conclusions: Dynamic corneal response assessed by Corvis ST shows evidence of biomechanical changes consistent with decreasing stiffness with increasing levels of myopia in multiple parameters. The strongest correlations were with highest concavity parameters where the sclera influence is maximal.
Highlights
Myopia is the most common eye disorder in the world with a worldwide prevalence of more than 22% (Wu et al, 2015)
In recent years a wide variety of work has been completed on corneal biomechanics in health and disease with the introduction of non-invasive devices able to measure in vivo biomechanical parameters (Perez-Rico et al, 2015; Lee et al, 2016b; Vinciguerra et al, 2016)
Our results suggest that among the corneal biomechanical parameters assessed by Corvis ST and Ocular Response Analyzer (ORA), the parameters related to the highest concavity (HC) phase during the assessment by Corvis ST demonstrate a significant difference with increasing levels of myopia, and the strongest correlations
Summary
Myopia is the most common eye disorder in the world with a worldwide prevalence of more than 22% (Wu et al, 2015). The cornea is a viscoelastic tissue and corneal biomechanics, including the material properties of the cornea, determine its shape. A better understanding of corneal biomechanical response can allow for better diagnosis and staging of various corneal disorders, refinement of suitable patients for refractive surgery or intrastromal ring segment implantation and provide further insights into biomechanics-modulating treatments such as corneal crosslinking (CXL) and keratoplasty (Kling and Hafezi, 2017; Ziaei et al, 2019, 2020). The analysis and evaluation of corneal biomechanics is complex as the cornea is a viscoelastic tissue
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