Abstract
Purpose :
The detection of pre-clinical keratoconus remains a challenging task. We propose to use wave-based optical coherence elastography to measure full spatial-dependent elasticity of normal and keratoconic corneas. We hypothesize that both advanced and pre-clinical keratoconus corneas can be identified as outliers from a baseline metric.
Methods :
A 500 kHz ultrasonic air-coupled transducer co-focused with an optical coherence tomography system was used to generate quasi-harmonic mechanical perturbation at the corneal apex. Lamb wave propagation speed and average thickness were measured within 16 corneal meridians covering 360 degrees during 1s of acquisition. Measurements were conducted in thirty-one human healthy subjects (control group, N = 62 corneas; age: 20-50 yo; corneal astigmatism <2 diopters) and three keratoconic patients (N = 5 corneas; age: 14-50 yo). All measurements were fully non-contact, and followed the approved research protocol adhered to the tenets of the Declaration of Helsinki. Spatial anisotropy of wave speed (SAWS) was calculated from the meridional-dependent wave speed of each cornea. Speed and thickness for each corneal meridian were projected in a thickness-speed map (TSM) for further statistical analysis.
Results :
SAWS was statistically significantly higher in advanced (0.353, p = 1×10-11, N = 3) and pre-clinical (0.249, p = 0.04, N = 2) keratoconus corneas when compared to the baseline. Moreover, we found a linear correlation between meridional speed and thickness (RMSE = 0.738, p = 5.4×10-98) in normal corneas when measurements were projected into the TSM (Fig. 1). A 95% confidence level was used as a baseline metric to separate normal (stiffer) from abnormal (softer) corneal elasticity. We found abnormal elasticity in at least 10 out of 16 meridians in advanced keratoconus corneas (p = 1×10-10, N = 3), and in at least in 4 out of 16 meridians in pre-clinical keratoconus corneas (p = 1.5×10-5, N = 2).
Conclusions :
Our results show important biomechanical differences in SAWS and TSM between normal and keratoconus corneas, suggesting those as potential biomarkers for progression and severity of keratoconus, following sensitivity and specificity studies on a larger sample of keratoconic (and their contralateral) eyes.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.