Biomechanical properties of cornea and ocular aberrations in myopic eyes

Purpose:To study the correlation of corneal topography, corneal biomechanical properties, and ocular aberrations with the magnitude of refractive error in myopic eyes. Methods:All myopic patients attending the clinic for refractive surgery were recruited. Data recorded included visual acuity, axial length (AL), central corneal thickness (CCT), manifest refraction spherical equivalent (MRSE), topography (Pentacam - Oculus), corneal biomechanical factors [ocular response analyzer (ORA)], and optical aberrations (iTrace). They were further categorized into group 1 (suitable for femto-LASIK) and group 2 (unsuitable for femto-LASIK). Results:Sixty eyes (30 myopes) of mean age 22.78 +/- 2.71 years were enrolled. A negative correlation of refractive error was noted with AL (rho = -0.9; P < 0.001), total aberrations (rho = 0.53; P < 0.001), and lower-order aberrations (LOA) (rho = 0.54; P < 0.001). A strongly positive correlation was noted between CCT and corneal hysteresis (CH) (rho = 0.63; P < 0.001), CCT and CRF (rho = 0.56; P < 0.001), CH and corneal resistance factor (CRF) (rho = 0.83; P < 0.001), and Goldmann equivalent intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) (rho = 0.78; P < 0.001). An increase in higher-order aberrations (HOAs) as well as lower-order aberrations (LOAs) was noted with increasing sim-K [HOA (r = 0.73, P = 0.001); LOA (r = 0.601, P = 0.014)] and increasing CRF [HOA (r = 0.5, P = 0.006); LOA (r = 0.732, P = 0.001)] in group 2. The amount of refractive error, axial length, central corneal thickness, and sim-K were significantly different in the two groups. Conclusion:Increasing degree of myopia is associated with an increase in axial length, total aberrations, and lower-order aberrations. Corneal biomechanical parameters have a strong correlation with each other. Lower corneal biomechanics are noted in high myopes as they have weaker and thinner corneas. Corneal biomechanics and ocular aberrations do not differ significantly between cases suitable for femto-LASIK and cases unsuitable for femto-LASIK.