Change in corneal biomechanical properties and influence factors in population with myopia

Background

Corneal refractive surgery has significant effects on corneal biomechanical properties.However, there are few study on large scale population with corneal biomechanical properties in the myopic population before corneal refractive surgery.

Objective

This study was to evaluate the change of corneal biomechanical properties and influence factors in myopic eyes using ocular response analyzer (ORA).

Methods

A prospective cohort study was carried out in Beijing Tongren Eye Center from April 2010 to January 2011.Corneal hysteresis (CH) and corneal resistance factor (CRF) were detected using ORA in 1 792 eyes of 896 myopic subjects who were going to receive corneal refractive surgery under the informed consent.According to different spherical equivalent (SE) the eyes were grouped into -0.25-<-3.0 D group, -3.0-<-6.0 D group, -6.0-<-9.0 D group, -9.0-<-12.0 D group, -12.0-<-15.0 D group and ≥-15.0 D group and according to different central corneal thickness (CCT), the eyes were grouped into <500 μm group, 500-<550 μm group, 550-<600 μm group and≥600 μm group.The CH value and CRF value in different SE groups or different CCT groups were compared, and the factors influencing CH and CRF were analyzed by Pearson correlation analysis.

Results

The mean CH and CRF value were (9.84±1.52)mmHg (1 mmHg =0.133 kPa) and (10.46±1.71)mmHg, respectively in the myopic eyes.The CH values were (10.35±1.53), (10.07±1.55), (9.81±1.46), (9.71±1.59), (9.35±1.55) and (9.23±1.28)mmHg in the -0.25-<-3.0 D group, -3.0-<-6.0 D group, -6.0-<-9.0 D group, -9.0-<-12.0 D group, -12.0-<-15.0 D group and ≥-15.0 D group, respectively, showing a significant difference among the groups (F=20.69, P<0.01), and the CH values in the -6.0-<-9.0 D group, -9.0-<-12.0 D group, -12.0-<-15.0 D group and ≥-15.0 D group were significantly lower than those in the -6.0-<-9.0 D group, -9.0-<-12.0 D group (all at P<0.01). There was no significant difference in the CRF values among different SE groups (F=0.65, P=0.49). CH and CRF values were increasing with the raise of CCT, with evidently differences among the CCT<500 μm group, 500 μm ≤CCT<550 μm group, 550 μm≤CCT<600 μm group and CCT≥600 μm group (CH: F=110.99, P<0.01; CRF: F=84.35, P<0.01), and the CH and CRF values were significantly higher in the 550 μm≤CCT<600 μm group and CCT≥600 μm group than those in the CCT<500 μm group (all at P<0.01). CH showed a positive correlation with SE (r=0.24, P<0.01), and no significant correlation between CRF and SE (r=0.03, P=0.20). The CH and CRF showed the positive correlations with the CCT (r=0.42, 0.57, both at P<0.01). In addition, CH and CRF values increased as the increases of SE, corneal curvature (CC) and CCT values, with the regression equation of CH=-7.87+ 0.08SE+ 0.16CC+ 0.02CCT (R²=0.26, P<0.01) and CRF=-11.42+ 0.14CC+ 0.03CCT (R²=0.34, P<0.01), respectively.The CH and CRF did not change with the age and gender in the subjects.

Conclusions

Corneal biomechanical properties including CH and CRF were positively correlated with CCT, CC and SE.