In vivo determination of the human corneal elastic modulus by VOCT

Abstract

Purpose : Vibrational optical coherence tomography (VOCT) supplements traditional optical coherence tomography with soundwaves to obtain the resonant frequency (RF) and the elastic modulus of anatomical structures. In this prospective study, we used VOCT to determine the in vivo elastic modulus of the human cornea.

Methods : Central corneal thickness measurements obtained from VOCT were correlated with those of Pentacam® (Oculus; Wentzler, Germany) pachymetry. VOCT measurements were performed at two different locations [central cornea (CC) and inferior cornea (IC)] in 32 normal eyes from 16 subjects. The RF and thickness values obtained from VOCT were employed in a calibration equation to calculate the corresponding modulus value. Repeated measurements were obtained in a subset of 10 eyes to assess the effect of anesthetic drops on the agreement of measurements.

Results : VOCT thickness values demonstrated a positive (r²=0.97) and linear correlation (y = 0.939x - 13.92) to those of Pentacam. Five peaks (#1-5) were identified on the weighted displacement vs. frequency plots, although their presence was variable across eyes. The mean RF values for peaks #1-5 on the CC were 73.5±4.9, 120.4±2.0, 148.7±8.0, 207±7, and 239±3 Hz, respectively. The mean RF values for peaks #1-5 on the IC were 72.1±6.3, 120.3±1.8, 147.2±6.7, 205±7, and 238±4 Hz. Based on the corresponding RF, the calculated elastic modulus for peaks #1-5 on the CC were 1.023±0.104, 2.05±0.16, 2.94±0.40, 5.31±0.37, and 6.87±0.33 MPa, respectively. The IC elastic modulus for peak #1-5 were 0.975±0.150, 1.991±0.236, 2.76±0.28, 5.08±0.73, and 6.52±0.79 MPa. The effect of topical anesthesia in elastic modulus values for each peak was not significant (p>0.05), except for peak #2 in the CC (p<0.05).

Conclusions : This pilot study demonstrates the utility of VOCT as an in vivo, non-invasive technology to measure the elastic modulus in human corneas. The structural origin of the various moduli obtained can be hypothesized based upon reported in vitro studies, but further analyses are necessary for confirmation.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1. Representative output of weighted displacement vs. frequency spectrum displaying resonant frequency peaks #1-5.

 

Figure 2. Elastic modulus values for resonant frequency peaks #1-5 for (a) central and (b) inferior cornea in 32 eyes.