Corneal biomechanical weakening presumably precedes keratoconus (KC), an ocular disease that leads to vision loss. Cross-meridian swept-source OCT coupled to air-puff excitation was used to induce corneal deformation to investigate biomechanics in Forme Fruste (FF)/subclinical (n=10), KC I (n=10) and healthy (n=12) eyes. Shape and asymmetry deformation parameters were analyzed in two meridians, and the tangent modulus was calculated using Finite Element modeling (FEM). Compared to healthy eyes, the asymmetry parameter decreased 0.32±0.05% (FF/subclinical), and 0.66±0.18% (KC I). The shape parameter increased 0.91±0.32% (FF/subclinical) and 1.47±1.2% (KC I). Significant differences between groups were observed mostly on the vertical meridian. Inverse FEM showed ∼30% localized stiffness reduction in KC eyes, compared to healthy eyes. Our results show that the additional vertical meridian allows more significant use of deformation parameters as biomarkers of biomechanical changes.
The ability to perform multi-meridian, simultaneous OCT measurements of air-induced corneal deformation is expected to highly improve the accuracy of assessing corneal biomechanics. We propose a simplified method targeting 3-D deformation measurement that could be introduced to swept-source OCT systems. We utilize a spatial-depth-encoded multiplexing to provide a 9-spot measurement of the deformation. The method is promising for the assessment of corneal asymmetries and diagnosis of corneal pathologies such as keratoconus. We present in detail the system and key requirements to provide simultaneous 9-spot deformation measurement. Finally, results on porcine eyes ex vivo and human eye in vivo are presented.
Quantification of the corneas´ biomechanical properties helps to diagnose corneal abnormalities early, which is key in keratoconus (KC) management and treatment. We recently introduced a multi-meridian air-puff ssOCT system capable of acquiring corneal deformation images during air-puff excitation on two meridians. Two healthy and three KC patients were measured with the system. The results were used to quantify deformation asymmetries and as input data for Finite Element (FE) modeling, which was used to estimate corneal biomechanical properties by means of an inverse analysis. Deformation asymmetry parameters and the estimated tangent modulus for healthy and KC corneas are presented and compared.
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