Corneal Biomechanical Properties Of Low, Moderate And High Myopic Eyes

Corneal biomechanical response has gained interest in the last years, being studied in both health and disease.  Its better understanding may help in the diagnosis and staging of several corneal conditions, refinement of criteria for keratorefractive procedures and provide further insights into biomechanics-modulating treatments such as corneal crosslinking and keratoplasty. This study sought to investigate the relationship between corneal biomechanical properties and the degree of myopia using the Corvis ST (Oculus, Wetzlar, Germany).

Cross-sectional, unicenter, Refractive Surgery Unit of Ophthalmology Department of Centro Hospitalar Universitário do Porto, Oporto, Portugal. According to the spherical equivalent (SE), the suitable patients were divided into three groups: low (SE ≥ − 3.00D), moderate (SE -3.00D to -6.00D) and high (SE ≤ − 6.00D) myopia. 

Corneal biomechanics were assessed with Corvis ST (Oculus, Wetzlar, Germany) using the first (A1) and second (A2) applanation and the highest concavity (HC) times (T), velocities (V), deformation amplitude (DA) and deflection length (DefLength), amplitude (DefAmp) and area (DefArea). Integrated radius (IR); whole eye movement time (WEMms) and length (WEMmm); stiffness parameter (SP-A1), biomechanically corrected intraocular pressure (BIOP); Stress Strain Index (SSI) and Corvis biomechanical index (CBI) were also considered. A linear mixed-effects model was designed to assess the differences in the corneal biomechanics between groups, adjusting for age and sex. 

This study enrolled 363 eyes from 184 myopic patients (38% men), including 118, 166 and 79 eyes with low, moderate and high myopia, respectively. Mean±SD SE was -4.48±2.99D, ranging from -24.25 to -0.50D. Compared with the low myopia group, patients with moderate myopia had lower A2-DA (ß= -0.022, p=0.008)and lower WEMmm (ß= -0.018, p=0.014) whereas the high myopes presented higher A2-V (ß=-0.013, p=0.006), lower A2-DA (ß= -0.028, p=0.006), higher HC-DefLength (ß=0.166, p=0.014), higher HC-DefAmp (ß=0.182, p=0.012), lower WEMmm (ß= -0.028, p=0.012) and lower SSI (ß= -0.105, p<0.001). Compared with the moderate myopia group, patients with high myopia presented higher A2-V (ß=-0.014, p=0.001) and lower SSI (ß= -0.068, p=0.005).

Our results suggest a more deformable cornea with increasing levels of myopia. Higher values of A2-V and lower values of SSI were found with increasing grades of myopia, suggesting that these variables may be indicators of corneal elasticity. Overall, our work comes in line with the literature, supporting the idea that a softer corneal and scleral profile may influence the pathogenesis of myopia. As this is a cross-sectional study, no causal relationship can be attributed. Further studies exploring the predictive role of corneal biomechanics in myopia progression are warranted.