Alignment Between Corneal Biomechanical Anisotropy and Toricity Using Optical Coherence Elastography

To evaluate the agreement in orientation and magnitude between corneal toricity and biomechanical anisotropy using optical coherence elastography (OCE).

College of Optometry, University of Houston, Houston, Texas, USA.

Prospective cross-sectional study.

Healthy participants with spherical refractive error or corneal astigmatism > 0.50D were included. Corneal radial mechanical wave propagation speed, a proxy for corneal shear modulus, was measured using air-pulse wave-based OCE imaging (30° intervals over 360°). Biomechanical principal meridian () was defined as meridian with greatest wave speed, and its magnitude was calculated as difference between principal and orthogonal meridians. Likewise, astigmatic principal meridian () was defined as steep corneal meridian from videokeratography, and its magnitude was defined as dioptric difference between orthogonal steep and flat meridians. To compare these different domains (biomechanical anisotropy and astigmatism) within and across subjects, both vector magnitudes were cohort-normalized. Directional alignment between and was assessed using polar double-angle plots. Vectorial difference between these measures quantified similarities in both orientation and magnitude.

30 eyes from 30 subjects were studied. Corneal astigmatism ranged from 0.15 to 3.66D (1.4±0.8D; mean±SD). Corneal wave speed in steep meridian was faster (12.97±1.6m/s) compared to flat meridian(9.03±1.8m/s). Biomechanical anisotropy strongly correlated with astigmatism (R2 = 0.88). Angular difference between and was 6.0°±7.1° among astigmatic eyes. Cohort-normalized magnitude difference between and was 0.06±0.07.

In vivo human corneal wave-based OCE measurements demonstrate that corneal biomechanical anisotropy exhibits an orthogonal pattern, highly correlated in orientation and magnitude with corneal topography.