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. 2020 Nov 19;20(1):459.
doi: 10.1186/s12886-020-01729-x.

Effect of biomechanical properties on myopia: a study of new corneal biomechanical parameters

Fang Han  1   2   3 , Mengdi Li  1 , Pinghui Wei  1   4 , Jiaonan Ma  1 , Vishal Jhanji  5 , Yan Wang  6   7
Affiliations

Effect of biomechanical properties on myopia: a study of new corneal biomechanical parameters

Fang Han et al. BMC Ophthalmol. .

Abstract

Background: To assess the corneal stress-strain index (SSI), which is a marker for material stiffness and corneal biomechanical parameters, in myopic eyes.

Methods: A total of 1054 myopic patients were included in this study. Corneal visualisation Scheimpflug technology was used to measure the SSI. Corneal biomechanics were assessed using the first and second applanation times (A1-and A2-times); maximum deflection amplitude (DefAmax); deflection area (HCDefArea); the highest concavity peak distance (HC-PD), time (HC-time), and deflection amplitude (HC-DefA); integrated radius (IR); whole eye movement (WEM); stiffness parameter (SP-A1;, biomechanically corrected intraocular pressure (BIOP); and Corvis biomechanical index (CBI). Scheimpflug tomography was used to obtain the mean keratometery (Km) and central corneal thickness (CCT). According to the spherical equivalent (SE) (low myopia: SE ≥ - 3.00D and high myopia: SE ≤ - 6.00D.), the suitable patients were divided into two groups.

Results: The mean SSI value was 0.854 ± 0.004. The SSI had a positive correlation with A1-time ((r = 0.272), HC-time (r = 0.218), WEM (r = 0.288), SP-A1 (r = 0.316), CBI (r = 0.199), CCT (r = 0.125), bIOP (r = 0.230), and SE (r = 0.313) (all p-values<0.01). The SSI had a negative correlation with HCDefA (r = - 0.721), HCDefArea (r = - 0.665), HC-PD(r = - 0.597), IR (r = - 0.555), DefAmax (r = - 0.564), and Km (r = - 0.103) (all p-values<0.01). There were significant differences in SSI (t = 8.960, p<0.01) and IR (t = - 3.509, p<0.01) between the low and high myopia groups.

Conclusions: In different grades of myopia, the SSI values were lower in eyes with higher SEs. It indicates that the mechanical strength of the cornea may be compromised in high myopia. The SSI was positively correlated with the spherical equivalent, and it may provide a new way to study the mechanism of myopia.

Keywords: Corneal biomechanics; Corneal stress-strain index; Myopia.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Schematic view of the Corvis ST test and cornea deformations. The air puff impinges (pink line) on the corneal surface, the cornea becomes concave and whole eye motion (green line) is simultaneously initiated in the backward direction. Deformation amplitude: deformation of the corneal apex (red line). Deflection amplitude (mm): displacement of corneal apex y after eye motion in removed (blue lines). Corvis ST: corneal visualisation Scheimpflug technology
Fig. 2
Fig. 2
Scatter plots showing significant correlation between SSI and spherical SE (r = 0.313, p<0.01). SSI: stress-strain index; SE: spherical equivalent
Fig. 3
Fig. 3
Histogram comparison of parameters in low and high myopia. The x axis represents the parameters for comparison between low and high myopia. The y axis represents the numerical value of the paramete. CCT: central corneal thickness; ARTh: ambrosio relation thickness horizontal DAmax: maximum deformation amplitude; CBI: Corvis biomechanical index; SSI: stress-strain index
Fig. 4
Fig. 4
Scatter plots showing correlations of SSI with DefAmax (r = − 0.564, p<0.01), Peakdist (r = − 0.597, p<0.01), HCDefA (r = − 0.721, p<0.01), HCDefArea (r = − 0.665, p<0.01). SSI: stress-strain index; DefAmax: maximum deflection amplitude; PD: Peak distance; HCDefA: highest concavity deflection amplitude; HCDefArea: highest concavity deflection area
See this image and copyright information in PMC

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