Abstract
Purpose :
In vivo biomechanical characterization of the cornea remains a challenge. We have developed a high-resolution ultrasound elastography method to measure corneal axial displacement (CAD) induced by the ocular pulse. Here we compared CAD and a stiffness index derived from CAD between keratoconus patients and normal controls. We also explored the trend of these parameters with keratoconus grade.
Methods :
Twenty normal controls (40 eyes) and 20 keratoconus patients (35 eyes) were recruited. Each subject underwent three tests: (1) OCULUS Pentacam for corneal topography; (2) PASCAL Dynamic Contour Tonometry for intraocular pressure (IOP) and ocular pulse amplitude (OPA), and (3) ocular pulse elastography (OPE) for CAD using the Vevo2100 ultrasound system. Corneal topography data was reviewed by a specialist (AH) to determine the presence and grade of keratoconus. Four ultrasound measurements were performed in each eye, and each measurement acquired an 8-second video of the cornea during fixation. This data was processed to obtain the average CAD following published protocols [Kwok et al, TVST, 2020; 9(13):33]. Corneal stiffness index was calculated as OPA/CAD for each eye. Linear mixed models for repeated measures were used to account for association between two eyes of the same subject in data analysis.
Results :
Mean CAD (unit: µm) was significantly higher (p=0.0088, Fig. 1A) in keratoconus (46.6, 95% CI: 39.2, 53.9) than normal (34.6, 95% CI: 30.1, 39.1). Mean corneal stiffness (unit: mmHg/µm) was significantly lower (p=0.0068, Fig. 1B) in keratoconus (0.0522, 95% CI: 0.0384, 0.066) than normal (0.0804, 95% CI:0.0666, 0.0942). Age and IOP were not different between groups. Overall, mean CAD increased while corneal stiffness decreased at higher keratoconus grade (p=0.002 and 0.011, Fig. 2).
Conclusions :
This study confirmed the biomechanical weakening in keratoconus and suggested that this weakening worsened in more severe cases. Ultrasound elastography may provide a quick (minutes) and safe (no applied forces) biomechanical evaluation of the cornea to aid in keratoconus diagnosis.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.