The impact of LASIK surgery on corneal biomechanics remains unclear. To address this, we used air-coupled ultrasonic optical coherence elastography (ACUS-OCE) system to examine the full spatial-dependent elasticity of corneas before and after LASIK. We measured Lamb wave propagation speed and average corneal thickness in 16 semi-meridians to calculate the Shear Modulus (G) in 30 healthy control subjects (n=60 corneas) and 8 patients (n= 16 corneas) pre- and 1-month post-LASIK. G decreased from 52±4 kPa to 43±5 kPa after LASIK intervention. In summary, LASIK decreased corneal stiffness, which is consistent with the loss of anterior stroma containing high lamellae interweaving.
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 detection of subclinical keratoconus in human corneas remains a challenging task. We propose to use a wave-based air-coupled ultrasonic optical coherence elastography system to map the elasticity of the corneas of 15 patients with a clinical diagnosis of keratoconus (KC) in one eye, and subclinical keratoconus (SK) in the fellow eye. Two biomarkers are proposed: Spatial Anisotropy of Wave Speed (SAWS), and the Speed-Thickness Index (STI). Our results show important biomechanical differences between normal, subclinical, and advanced stages of keratoconus, suggesting SAWS and STI as potential biomarkers to identify “at-risk” corneas before changes in topography and pachymetry become evident.
The measurement of ocular biomechanics has a fundamental role in the diagnostics of ocular pathologies, and the monitoring of corneal treatments. In this work, we present success cases of clinical translation of wave-based optical coherence elastography to map the elasticity of human corneas in the following applications: (1) diagnosis and staging of keratoconus; (2) evaluation of the biomechanical impact of keratoconus treatments (UV-crosslinking, intrastromal ring segments, and corneal transplants); and (3) assessment of elastic changes in corneas after LASIK refractive surgery. This work contributes towards the development of a more effective diagnosis and customized treatment of eye diseases that will support ophthalmologists during their clinical decision-making.
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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