Journal d'ophtalmologie clinique et expérimentale
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The Relationship between Corneal Biomechanics and Corneal Shape in Normal Myopic Eyes

Lin Zhang, Yan Wang, Lili Xie, Weili Geng and Tong Zuo

Objectives: To investigate the possible association between corneal biomechanical parameters and morphological properties in a normal myopic population.
Methods and patients: The study consisted of 480 normal myopic eyes (240 healthy volunteers), with ages ranging from 18 to 44 years (mean, std 23.84 ± 5.08 years), and mean spherical equivalent (MSE) ranging from -14.00 to -1.13 D (mean, std –5.68 ± 2.17 D). Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using the Ocular Response Analyser (ORA; Reichert Ophthalmic Instruments, Depew, New York, USA) in both eyes. Pentacam (Oculus GmbH, Wetzlar, Germany, and software version 1.17r27) were used to obtain corneal central elevation and corneal asphericity (Q value within 6 mm diameters) of both anterior and posterior surfaces, corneal central thickness (CCT), corneal volume (CV) and corneal spherical aberration values. Corneal volume was calculated within diameters from 1.0 to 6.0 mm with 0.5 mm steps centered on the apex to create the corneal-volume distribution. Pearson correlation coefficient was used for analysis on relationships between CH, CRF and Pentacam parameters (CV, elevation, Q-value, spherical aberrations, et al).
Result: The values of CH and CRF presented normal distribution and the mean CH was (10.38 ± 1.36) mmHg, and the mean CRF was (10.70 ± 1.59) mmHg. There is a good correlation between CH, CRF and CCT (CH: r=0.54, P=0.000*, CRF: r=0.61, P=0.000*), and a stable correlation with each CV value (r≈0.5, P=0.000*) within central 6 mm diameter corneal region. On the other hand, CH and CRF were negatively correlated with anterior central elevation (CH: r=-0.136*, P=0.002*; CRF: r=-0.152*, P =0.001*), positively correlated with Q value of anterior surface (CH: r=0.136*, P=0.002; CRF: r=0.132*, P=0.003) and corneal spherical aberration (CH: r=0.184*, P=0.000*; CRF: r=0.191*, P =0.000*).
Conclusions: There is a homogeneous relationship displayed between corneal biomechanical parameters (CH and CRF) and corneal morphological features. Our results suggest high biomechanical values might be related to central flattening and oblate corneal shape.